Integrated Membrane Desalination Systems with Membrane Crystallization Units for Resource Recovery: a New Approach for Mining from the Sea

crystals

Article Integrated Membrane Desalination Systems with Membrane Crystallization Units for Resource Recovery: A New Approach for Mining from the Sea

Cejna Anna Quist-Jensen 1,2, Francesca Macedonio 1,2 and Enrico Drioli 1,2,3,4,* 1 National Research Council—Institute on Membrane Technology (ITM–CNR), Via Pietro BUCCI, c/o University of Calabria, cubo 17C, Rende 87036, Italy; [email protected] (C.A.Q.-J.); [email protected] (F.M.) 2 Department of Environmental and Chemical Engineering, University of Calabria, Rende 87036, Italy 3 WCU Energy Engineering Department, Hanyang University, Seoul 133-791, Korea 4 Center of Excellence in Desalination Technology, King Abdulaziz University (KAU–CEDT), Jeddah 21589, Saudi Arabia * Correspondence: [email protected]; Tel.: +39-098-449-2039

Academic Editor: Helmut Cölfen Received: 28 January 2016; Accepted: 29 March 2016; Published: 1 April 2016

Abstract: The mining industry is facing problems of clean production in terms of mineral processing, pollution, water consumption, and renewable energy. An interesting outlook can be to combine the mining industry with membrane-based desalination in the logic of mining from the sea. In fact, several of the drawbacks found in both mining and desalination can be minimized or overcome, which includes hindering mineral depletion, water production instead of water consumption, smart usage of brine instead of disposal, and low energy consumption, etc. Recently, membrane crystallization (MCr) has been developed to recover minerals from highly concentrated solutions. This study suggests MCr for the treatment of nanoﬁltration (NF) retentate and reverse osmosis (RO) brine leaving membrane-based desalination system. Thermodynamic modeling has been carried out to predict at which water recovery factor and which amount of minerals can be recovered. Theoretical results deviate only 2.09% from experimental results. Multivalent components such as barium, strontium, and magnesium are easier to recover from NF retentate with respect to RO brine. KCl and NiCl2 might be recovered from both NF retentate and RO brine, whereas lithium can only be recovered from RO brine. Moreover, copper and manganese compounds might also be recovered from desalination brine in perspectives.

Keywords: valuable resource recovery; membrane crystallization; mining industry; thermodynamic modeling; membrane-based desalination

1. Introduction The world of today and future development are highly dependent on an adequate supply of minerals from the mining industry. Mining, like many other industries, is required to change towards more sustainable production methods. Today, the mining industry is facing problems of sustainable water supply, renewable energy sources, and depletion of minerals. Moreover, as the ore grades degrade, the higher the associated production costs become, including water and energy consumptions. At the same time, population increase, climate changes, and ongoing industrialization are also putting pressure on water, energy, and minerals. These resources are, moreover, limited and cannot be used without any concern. Fresh water resources are sufﬁcient only in limited parts of the world. It is estimated that 50% of the world population will live in water stressed regions in 2025, which highlights the importance of adequate water management and treatment [1]. For this reason, the mining industry

Crystals 2016, 6, 36; doi:10.3390/cryst6040036 www.mdpi.com/journal/crystals Crystals 2016, 6, 36 2 of 13 is also forced not to deplete or contaminate the existing water resources, and at the same time not to risk the water supply of the local community. Water in mining is becoming a hot topic and some countries have restricted the mining industry to protect their own water. Energy consumption grew rapidly in the last decades and is projected to increase further in the following years [2]. Furthermore, mineral deficiency is also a threat to future development. Therefore, the conventional mining industry has several constrains for a sustainable way of production. Seawater can be an additional source for mineral extraction. The most part of the ions present in the periodic table might be recovered from seawater in the logic of “mining from the sea”. Historically, mining from the sea was considered during the oil crisis of the 1970. Yet, it never reached breakthrough due to several deficiencies, including high cost, low efficiency, lack of technological development, etc. In reality, the proposed strategy of direct recovery from seawater is difficult and might still be an impossible task. However, it can be brought back to life in another context with respect to the 1970ties, and due to improved technological processes, higher risks of mineral depletion, requirements of sustainable water and energy sources. The problems that the mining industry is facing today, such as water, energy and minerals deficiency, can partly be solved by introducing membrane technology. Membrane engineering is aligned with sustainable development, which has become important for many industrial processes. However, lack of a precise definition of sustainable development has evolved specific guidelines, such as the process intensification strategy (PIS) helping to meet the requirements of sustainable development. Membrane engineering, through the process intensification strategy, can redesign conventional process engineering with applications in several industrial processes; e.g., wastewater treatment, desalination, and many other applications where separation is needed [3]. Membrane engineering meets the goals of PIS for several reasons, including high selectivity and permeability for transport of specific components, ease of integration with other processes or other membrane operations, less energy intensive, high efficiency, low capital costs, small footprints, high safety, and operational simplicity and flexibility [4–7]. Membrane engineering can be an interesting outlook for the mining industry, for example, by associating mining and desalination. Not only can desalination contribute to mining by water production, but it can also contribute to energy production and minerals recovery. These kind of desalination systems are already being developed in large-scale desalination projects; e.g., Global MVP. Desalination is one of the industries that has changed from conventional processes to membrane technology, where reverse osmosis (RO) desalination today accounts for more than 60% of the capacity [8]. There have been many developments over the last three decades which have contributed to a reduction in unit water cost of RO desalination, particularly: membrane performance and decrease of membrane cost, reduction in energy consumption, improvements in pretreatment processes, increases in plant capacity, etc. [9]. However, one of the limitations of RO desalination is the relatively low water recovery factor (~40%–60%). Due to the increase in salinity, and therefore the required applied pressure (driving force), it is not economically or technically feasible to go beyond this recovery factor. Other potential improvements for RO desalination include better exploitation of the RO brine and reduction in electrical energy consumptions. Several international large-scale desalination projects are renewing desalination to reduce the cost and increase efficiency. Some of these are: MEDINA (Membrane Based Desalination: An Integrated Approach 2006–2010, European project) [10], SEAHERO (Seawater engineering & architecture of high efficiency reverse osmosis 2007–2012, 2013–2018, S. Korea) [11], MEGATON (2009–2014, Japan) [12,13], Global MVP (2013–2018, Korea) [13]. The large-scale projects are, for example, investigating the feasibility of novel membrane operations to increase water recovery, reduce brine disposal, and implement energy production. The novel membrane operations are membrane distillation (MD) for enhancing water recovery and pressure retarded osmosis (PRO), or reverse electrodialysis (RED) for energy production. The latest launched project, the Global MVP, aims to further develop the so-called 3rd generation desalination plant by also introducing an additional step for valuable resource recovery. The Global MVP project Crystals 2016, 6, 36 3 of 13

Crystals 2016, 6, 36 3 of 13 emphasizes lithium and strontium recovery from the discharged RO brine [13], but in fact, several otherTo constituents recover minerals might alsofrom be highly recovered concentrated from RO solutions, brine. a new and very interesting membrane technology—To recoveri.e., minerals membrane from crystallization highly concentrated (MCr)—has solutions, been developed a new and within very interesting the last 30 years. membrane MCr technology—is able to treati.e., solutions,membrane which crystallization are difficult(MCr)—has to treat for otherbeen unit developed operations within in theterms last of 30 costs, years. energy MCr isconsumption, able to treat crystal solutions, quality which and are quantity, difﬁcult etc. to treat for other unit operations in terms of costs, energy consumption, crystal quality and quantity, etc. 1.1. Membrane Crystallization (MCr) 1.1. Membrane Crystallization (MCr) MCr is an extension of the MD concept based on mass transfer through a microporous hydrophobicMCr is anmembrane extension (Figure of the 1). The MD driving concept force based is normally on mass a temperature transfer through gradient a microporous between the hydrophobictwo membrane membrane sides. The (Figure hydrophobic1). The drivingnature of force the ismembrane normally prevents a temperature liquid gradientintrusion between into the thepores. two Therefore, membrane only sides. volatile The hydrophobic components nature are oftransported the membrane through prevents the liquidmembrane intrusion and intoare thecondensed pores. on Therefore, the permeate only site. volatile The componentsmass transfer are of transportedvolatile solvents through allows the concentration membrane and of feed are condensedsolutions above on the their permeate saturation site. limit, The mass thus transferattaining of a volatile supersaturated solvents allowsenvironment concentration where crystals of feed solutionsmay nucleate above and their grow. saturation The advantages limit, thus of using attaining MD and a supersaturated MCr are the very environment low utilized where temperatures crystals mayand pressures, nucleate and high grow. permeate The advantages quality independent of using MD of and feed MCr characteristics are the very (theoretical low utilized 100% temperatures rejection andof non-volatile pressures, highcomponents), permeate simple quality configuration, independent ofand feed the characteristics possibility to (theoretical treat highly 100% concentrated rejection ofsolutions non-volatile [14]. Unlike components), pressure simple driven conﬁguration, membrane operations, and the possibilitythe impact toof treatconcentration highly concentrated in MD and solutionsMCr is very [14]. small Unlike [15]. pressure Therefore, driven membranethese proces operations,ses are perfect the impact to treat of concentration the brine leaving in MD andRO MCrdesalination. is very small Furthermore, [15]. Therefore, MCr these has processessome important are perfect advantages to treat the brinewith leavingrespect RO to desalination.traditional Furthermore,crystallization MCr processes, has some importantsuch as advantageswell-controlled with respectnucleation to traditional and growth crystallization kinetics, processes, faster suchcrystallization as well-controlled rates and reduced nucleation induction and growth time, cont kinetics,rol of super-saturation faster crystallization level and rates rate. and Therefore, reduced inductionit is possible time, to target control the ofcrystal super-saturation polymorph form level to and obtain rate. crystals Therefore, with narrow it is possible size distribution to target and the crystalhigh purity polymorph [16]. form to obtain crystals with narrow size distribution and high purity [16].

Figure 1. Membrane distillation and membrane crystallization concept.

This study suggests a paradigm shift in the mining industry by combining minerals recovery and membrane desalination operations for water and mineral production, according to the scheme shown in Figure2 2.. SmartSmart integrationintegration ofof membranemembrane operationsoperations inin desalinationdesalination cancan contributecontribute toto thethe conventional mining mining industry industry by by re recoveringcovering minerals minerals from from the the brine. brine. At the At same the same time, time,it solves it solves some someof the ofdrawbacks the drawbacks of the mining of the miningand the anddesalinatio the desalinationn industry. industry. Membrane Membrane crystallizers crystallizers are operating are operatingat low temperatures at low temperatures (normally (normallybelow 60 °C) below and 60at ˝ambientC) and atpressure, ambient which pressure, reduces which the reduces associated the associatedenergy costs. energy The well-controlled costs. The well-controlled nucleation nucleationand growth and and growth the high and purity the high also purity ensure also less ensure post- lesstreatment post-treatment of the minerals of the minerals with respect with respectto the mini to theng mining industry. industry. At the At same the sametime timethat thatminerals minerals are being produced, MCr also produces a high-quality water stream. Therefore, the drawbacks of low water recovery factors and brine disposal in desalination can be minimized.

Crystals 2016, 6, 36 4 of 13 are being produced, MCr also produces a high-quality water stream. Therefore, the drawbacks of low water recovery factors and brine disposal in desalination can be minimized. Crystals 2016, 6, 36 4 of 13

Figure 2.2. IntegratedIntegrated membrane membrane desalination systemsystem for waterwater andand mineralmineral production.production. NF: Nanoﬁltration;Nanofiltration; RO:RO: ReverseReverse Osmosis;Osmosis; MD:MD: MembraneMembrane Distillation;Distillation; MCr:MCr: MembraneMembrane Crystallization.Crystallization.

2. Methods Methods Minerals recoveryrecovery has has been been considered considered through throug the integrationh the integration of membrane of membrane operations operations according toaccording the scheme to the illustrated scheme illustrated in Figure2. in Membrane Figure 2. Membrane distillation distillation and membrane and crystallizationmembrane crystallization have been appliedhave been to NF applied and RO to brine, NF and respectively. RO brine, In therespecti theoreticalvely. In evaluation the theoretical of minerals evaluation recovery, of aminerals capacity ofrecovery, the RO a unit capacity of 923 of mthe3/d RO has unit been of 923 assumed m3/d has (water been assumed recovery (water factor re ofcovery 52%), factor and from of 52%), this and the volumefrom this of the variousvolume otherof the streams various have other been stre estimatedams have (Tablebeen1 ).estimated Seawater (Table composition 1). Seawater and thecomposition corresponding and the ion corresponding rejection of the ion NF rejection and RO of membranethe NF and have RO membrane been shown have in Tablebeen 2shown. In the in simulation,Table 2. In the no simulation, calcium or carbonateno calcium compounds or carbonat aree compounds present, since are thepresent, brine since has been the brine considered has been to 2 3 3 3 4 beconsidered pre-treated to be with pre-treated Na2CO3 towith precipitate Na CO to CaCO precipitate3. CaCO CaCO3 and. CaSO CaCO4 are and considered CaSO are to considered be high risk to scalingbe high components,risk scaling components, and can therefore and can destroy theref orore impede destroy the or MCrimpede operation the MCr [17 operation]. For this [17]. reason, For calciumthis reason, and calcium carbonate and are carbonate not found are in not Table found2. in Table 2.

Table 1.1. Recovery rate, inlet volumevolume andand capacitycapacity ofof thethe respectiverespective membranemembrane units.units.

Unit OperationUnit Operation NF NF RO RO MD/MCr MD/MCr Recovery rate (%) 75.9 52 – Recovery rate (%) 75.9 52 – 3 Inlet toInlet unit to (m unit3) (m ) 25542554 1923 1923 923 923 RetentateRetentate (m3) (m3) 631631 923 923 – – 3 PermeatePermeate (m ) (m3) 19231923 1000 1000 – –

Table 2.2. Seawater compositioncomposition andand NFNF andand RORO ionion rejection.rejection.

ElementElement Seawater Seawater Concentration Concentration (ppm) (ppm) NF NFRejection Rejection RO Rejection RO Rejection BariumBarium Ba Ba 0.021 87.7 87.7 99.6 99.6 Chlorine Cl 19400 26.7 99.6 ChlorineCesium Cl Cs 0.0003 19400 87.7 26.7 99.6 99.6 CesiumCopper Cs Cu 0.00090.0003 87.7 87.7 99.6 99.6 Potassium K 392 26.7 99.6 CopperLithium Cu Li 0.0009 0.17 26.7 87.7 99.6 99.6 Magnesium Mg 1290 87.7 99.6 PotassiumManganese K Mn 0.0004 392 80.7 26.7 99.6 99.6 LithiumSodium Li Na 10800 0.17 26.7 26.7 99.6 99.6 Nickel Ni 0.0066 87.7 99.6 MagnesiumRubidium Mg Rb 12900.12 26.7 87.7 99.6 99.6 ManganeseSulfate Mn SO4 0.0004 2708 93.3 80.7 99.6 99.6 Strontium Sr 8.1 87.7 99.6 SodiumUranium Na U 0.0033 10800 40 26.7 99.6 99.6 Zinc Zn 0.005 26.7 99.6 Nickel Ni 0.0066 87.7 99.6 Rubidium Rb 0.12 26.7 99.6 Sulfate SO4 2708 93.3 99.6 Strontium Sr 8.1 87.7 99.6 Uranium U 0.0033 40 99.6 Zinc Zn 0.005 26.7 99.6

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Enrichment of the feed stream carried out by MD and MCr has been simulated through the geochemical software PHREEQC using the Pitzer speciﬁc-ion-interaction aqueous model [18]. The PHREEQC software utilized is PHREEQC interactive-version 3. The Pitzer approach takes into account the interaction between the different ions and is therefore suitable for highly concentrated solutions. The existing database in PHREEQC has been updated to match all the ions considered in Table2. To simulate water removal, a so-called “REACTION” has been utilized to remove a speciﬁed amount of water in a given number of steps. The output of the software provides saturation indices and the amount of compounds which have precipitated, etc. Temperature of RO brine and pH in the simulations has been assumed to 30 ˝C and 7, respectively. Clearly, the operative temperature can be adjusted to enhance or inhibit one compound to precipitate instead of another, which will be discussed in the following sections.

3. Results and Discussion Today, some minerals are already being extracted from seawater, such as Na+, Mg2+ and K+ [19]. Several research activities have been carried out to extend the number of ions to be recovered from seawater [19]. The ocean has, in general, a much greater content of mineral resources in comparison to on land [19,20]. Although, one can argue that the resources in the ocean are present in lower concentrations, which reduces the possibility of recovery. Nevertheless, mineral recovery might be too expensive and energy intensive with respect to extraction directly from seawater. Instead, it might be more economically feasible to recover minerals from NF retentate and RO brine and hereby turn waste streams into resources. In the following sections, the potential of minerals recovery from NF retentate and RO brine is highlighted.

3.1. Minerals Recovery from NF Retentate

The ﬁrst compounds to precipitate from NF retentate (Figure3) are BaSO 4 and SrSO4 (Barite and Celestite, respectively). These compounds can be interesting to recover due to their utilization in the oil and gas industry as weighing material or stabilizer in drilling mud [21]. According to U.S. Geological Survey, the average price of barium and strontium imported to USA in 2013 was 115 $/ton and 50 $/ton, respectively [22]. Simulations have proven that from 631 m3 of NF brine (Table1) it is possible to recover around 0.07 kg of barium and 40 kg of strontium. These might seem to be relatively low amounts, nevertheless, it has to be taken into consideration that at the industrial level, RO desalination plants have capacities ranging from 100,000 to 500,000 m3/d, and even higher capacities are projected. For example, from a seawater reverse osmosis (SWRO) plant with a capacity of 100,000 m3/d, it is potentially possible to recover 11.1 kg/d of barium and 6339 kg/d of strontium. Therefore, the future recovery potential is much higher than the one considered in this study. The larger amount of strontium can make this compound more feasible to separate from the RO brine with respect to barium [23]. However, due to the higher amount of NaCl (starting to precipitate above water recovery factor (WRF) of 86%), it has to be recovered before NaCl precipitation to avoid incorporation of strontium into the NaCl lattice [17]. After NaCl crystallization, magnesium sulfate, in the form of MgSO4¨ 7H2O (Epsomite), starts to precipitate at a WRF of 93% when the temperature is kept at 30 ˝C. Other polymorphs of magnesium sulfate and magnesium chlorides can also precipitate. However, experimental results carried out in earlier studies have shown that, by properly tuning the operative conditions, epsomite can be produced via MCr [24,25]. This highlights one of the very important advantages of MCr with respect to conventional crystallizer: in MCr it is easy to tune the polymorph structure by changing operative conditions [26,27]. From the NF retentate considered in this study, it is possible to recover approximately 25.6 kg/m3 of epsomite at a recovery factor of 98%. Minerals recovery found in this study is relatively higher with respect to experimental studies [24,28], but this is according to a higher WRF. Crystals 2016, 6, 36 6 of 13 Crystals 2016, 6, 36 6 of 13

Figure 3. Amount of compounds that can be recovered from NF retentate by membrane Figure 3. Amount of compounds that can be recovered from NF retentate by membrane crystallization. crystallization. Water recovery factor refers to the amount of water recovered from NF retentate. Water recovery factor refers to the amount of water recovered from NF retentate.

Figure 3 indicates that NiCl2 can precipitate above a WRF of 97%, but the simulation also shows Figure3 indicates that NiCl can precipitate above a WRF of 97%, but the simulation also shows that the precipitated amount starts2 to decrease soon after, which specifies that NiCl2 can re-dissolve. Thethat content the precipitated of nickel amountin the brine starts is tomuch decrease lower soon with after, respect which to other specifies chlori thatde NiCl compounds,2 can re-dissolve. such as The content of nickel in the brine is much lower with respect to other chloride compounds, such as NaCl, KCl, and MgCl2. In fact, it can be observed from Figure 3 that KCl and MgCl2 start to precipitate NaCl, KCl, and MgCl . In fact, it can be observed from Figure3 that KCl and MgCl start to precipitate at similar WRF. Therefore,2 the saturation index of NiCl2 decreases if chloride precipitates2 as KCl and at similar WRF. Therefore, the saturation index of NiCl decreases if chloride precipitates as KCl MgCl2. On the other hand, if the kinetics favors all three2 compounds, they might co-precipitate. and MgCl . On the other hand, if the kinetics favors all three compounds, they might co-precipitate. However, 2it can be possible to inhibit the precipitation of chlorides other than NiCl2 by controlling temperatureHowever, it canand be crystallization possible to inhibit kinetics. the precipitationControl of crystallization of chlorides other kinetics than is NiCl a difficult2 by controlling task in commontemperature crystallization and crystallization techniques, kinetics. but Control due to ofthe crystallization easy control kinetics of flux is through a difficult the task microporous in common membranecrystallization by techniques,changing operative but due toconditions the easy controlsuch as of flow flux throughrate and the temperature microporous and membrane hereby the by saturationchanging operative gradient, conditions it is easier such to tune/control as flow rate andthe temperaturekinetics in MCr. and herebyThe advantage the saturation of controlled gradient, growthit is easier andto shape tune/control has been the observed kinetics in in several MCr. The studie advantages on MCr, of controlledsuch as in the growth crystallization and shape hasof NaCl, been ¨ MgSOobserved4·7H in2O, several lysozyme, studies paracetamol, on MCr, such glutamic as in the acid, crystallization etc. [16,17,24,26,27]. of NaCl, MgSOYet, nickel4 7H 2precipitationO, lysozyme, fromparacetamol, NF retentate glutamic requires acid, experimentaletc. [16,17,24 ,verification.26,27]. Yet, nickel precipitation from NF retentate requires experimental verification. 3.2. Minerals Recovery from RO Brine 3.2. Minerals Recovery from RO Brine The minerals that can be recovered from RO brine have been illustrated in Figure 4. Most of the The minerals that can be recovered from RO brine have been illustrated in Figure4. Most of minerals precipitating from RO brine are also found to precipitate from NF retentate (Figure 3). It the minerals precipitating from RO brine are also found to precipitate from NF retentate (Figure3). should be noticed that, the fractionation of bivalent and monovalent ions, due to the NF membrane, It should be noticed that, the fractionation of bivalent and monovalent ions, due to the NF membrane, changes the route of precipitation. Hence, NaCl is the first salt to crystallize from RO brine. The changes the route of precipitation. Hence, NaCl is the first salt to crystallize from RO brine. bivalent ions, such as strontium, barium, and magnesium, are harder to precipitate from RO brine, The bivalent ions, such as strontium, barium, and magnesium, are harder to precipitate from RO which correspond to experimental literature data stating that magnesium cannot be recovered from brine, which correspond to experimental literature data stating that magnesium cannot be recovered RO brine [10,25]. from RO brine [10,25]. Lithium can precipitate as LiCl at a WRF of 97%. Lithium is of particular interest in the future due to the potential increase of lithium-ion batteries in electrical vehicles. Several studies discuss whether lithium resources on land suffice the increasing demand for lithium ion batteries [29–32]. In this logic, recovery from seawater can be an interesting contribution to the conventional mining industry. In fact, if all the disposed RO brine of today was utilized for lithium production, this could subsidize 13% of that obtained from mining [23]. Recently, lithium has been recovered from single salt LiCl solutions by means of membrane crystallizers [33]. However, it has been observed that lithium cannot be recovered by the normally used direct contact membrane distillation (DCMD) configuration of MCr (Figure1). The reason is the high solubility of LiCl, and therefore the driving force (vapor pressure difference) becomes negative prior to LiCl saturation. Instead of utilizing DCMD, the configuration has been changed to vacuum membrane distillation (VMD), where vacuum is present at the permeate side. In this configuration, the osmotic phenomenon has been removed and lithium can be recovered.

Figure 4. Amount of compounds that can be recovered from RO brine by membrane crystallization. Water recovery factor refers to the amount of water recovered from RO brine.

Crystals 2016, 6, 36 6 of 13

Figure 3. Amount of compounds that can be recovered from NF retentate by membrane crystallization. Water recovery factor refers to the amount of water recovered from NF retentate.

Figure 3 indicates that NiCl2 can precipitate above a WRF of 97%, but the simulation also shows that the precipitated amount starts to decrease soon after, which specifies that NiCl2 can re-dissolve. The content of nickel in the brine is much lower with respect to other chloride compounds, such as NaCl, KCl, and MgCl2. In fact, it can be observed from Figure 3 that KCl and MgCl2 start to precipitate at similar WRF. Therefore, the saturation index of NiCl2 decreases if chloride precipitates as KCl and MgCl2. On the other hand, if the kinetics favors all three compounds, they might co-precipitate. However, it can be possible to inhibit the precipitation of chlorides other than NiCl2 by controlling temperature and crystallization kinetics. Control of crystallization kinetics is a difficult task in common crystallization techniques, but due to the easy control of flux through the microporous membrane by changing operative conditions such as flow rate and temperature and hereby the saturation gradient, it is easier to tune/control the kinetics in MCr. The advantage of controlled growth and shape has been observed in several studies on MCr, such as in the crystallization of NaCl, MgSO4·7H2O, lysozyme, paracetamol, glutamic acid, etc. [16,17,24,26,27]. Yet, nickel precipitation from NF retentate requires experimental verification.

3.2. Minerals Recovery from RO Brine The minerals that can be recovered from RO brine have been illustrated in Figure 4. Most of the minerals precipitating from RO brine are also found to precipitate from NF retentate (Figure 3). It should be noticed that, the fractionation of bivalent and monovalent ions, due to the NF membrane, changes the route of precipitation. Hence, NaCl is the first salt to crystallize from RO brine. The bivalent ions, such as strontium, barium, and magnesium, are harder to precipitate from RO brine, which correspond to experimental literature data stating that magnesium cannot be recovered from Crystals 2016, 6, 36 7 of 13 RO brine [10,25].

Crystals 2016, 6, 36 7 of 13

Lithium can precipitate as LiCl at a WRF of 97%. Lithium is of particular interest in the future due to the potential increase of lithium-ion batteries in electrical vehicles. Several studies discuss whether lithium resources on land suffice the increasing demand for lithium ion batteries [29–32]. In this logic, recovery from seawater can be an interesting contribution to the conventional mining industry. In fact, if all the disposed RO brine of today was utilized for lithium production, this could subsidize 13% of that obtained from mining [23]. Recently, lithium has been recovered from single salt LiCl solutions by means of membrane crystallizers [33]. However, it has been observed that lithium cannot be recovered by the normally used direct contact membrane distillation (DCMD) configuration of MCr (Figure 1). The reason is the high solubility of LiCl, and therefore the driving force (vapor pressure difference) becomes negative prior to LiCl saturation. Instead of utilizing DCMD, the configuration has been changed to vacuum membrane distillation (VMD), where vacuum Figure 4. Amount of compounds that can be recovered from RO brine by membrane crystallization. is presentFigure at 4. theAmount permeate of compounds side. In thatthis can config be recovereduration, thefrom osmotic RO brine phenomenon by membrane hascrystallization. been removed Water recoveryrecovery factorfactor refersrefers toto thethe amountamount ofof waterwater recoveredrecovered fromfrom RORO brine.brine. and lithium can be recovered.

3.2.1. Experiments on Salts Recovery from RO Brine To verifyverify thethe suitability ofof the simulation study presented above as a useful tool for a preliminary preliminary analysis of the types and amount of salts to be extracted from the RO brine of desalination plants, and to effectively prove thethe capabilitycapability of MCrMCr toto produceproduce highhigh qualityquality crystals,crystals, somesome experimentalexperimental measurements were carried out. Experiments Experiments were were performed performed by by using the experimental set up described elsewhere [[25]25] andand shownshown inin FigureFigure5 5..

Figure 5. SchematicSchematic flow ﬂow sheet sheet of ofthe the MCr MCr lab labplant: plant: (A) cooler; (A) cooler; (B) pump; (B) pump; (C) flow-meter; (C) ﬂow-meter; (D) heater; (D) heater;(E) membrane (E) membrane module; module; (F) crystallizer (F) crystallizer tank; (G tank;) regulation (G) regulation valve; (H valve;) crystals (H) crystalsseparation separation system; system;(I) balance;(I) balance;(L) distillate(L) distillatetank; (S) external tank; (S temperature) external temperature sensor, (P) manometer; sensor, (P) manometer;and (T) temperature and (T) temperaturesensor. sensor.

The RO brine brine generated generated from from a adesalination desalination plant plant was was fed fed to the to theMCr MCr semi semi pilot pilot scale scale plant. plant. The 2 Theplant plant employed employed two two polypropylene polypropylene (PP) (PP) hollow hollow fibers fibers membrane membrane modules modules (E) (E) for for 0.2 0.2 m 2 of total membrane area. The plant was supplied with centrifugalcentrifugal pumps (B) and with the necessary tools for the controlcontrol of of the the most most significant significant parameters parameters of the of system: the system: flow rate flow and rate temperature. and temperature. The estimation The ofestimation the trans-membrane of the trans-membrane flux occurred flux by occurred evaluating by weightevaluating variations weight in variations the distillate in the tank distillate (L) with tank the balance(L) with (I). the The balance amount (I). of The ions amount in the crystallizing of ions in the solution crystallizing and in the solution distillate and were in the measured distillate through were ameasured conductivity through meter. a conductivity Crystals, when meter. formed, Crystals, were when removed formed, from were the plant removed through from the the crystals plant separationthrough the system crystals (H). separation The achieved system particles (H). The were achieved visually particles examined were with visually an optic examined microscope with an in orderoptic microscope to determine in crystal order to size, determine growth rate,crystal and size coefficient, growth ofrate, variation and coefficient (CV). of variation (CV). The experimental device operates in such a way that crystallization takes place in the crystallizer tank and not in the membrane module. This can be done with an appropriate control of temperature and flow rate. Table 3 summarizes the operating conditions used in the crystallization experiments.

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The experimental device operates in such a way that crystallization takes place in the crystallizer tank and not in the membrane module. This can be done with an appropriate control of temperature and ﬂow rate. Table3 summarizes the operating conditions used in the crystallization experiments. Crystals 2016, 6, 36 8 of 13 Table 3. Operating conditions used in the experiments. Table 3. Operating conditions used in the experiments. Feed Flow Rate (L/h) 200 Feed Flow Rate (L/h) 200 PermeatePermeate flow ﬂow rate rate (L/h) (L/h) 100100 Temperature at the MCr entrance/feed side (˝C) 39 ˘ 1 TemperatureTemperature at the at theMCr MCr entrance/feed entrance/permeate side (°C) side (˝C) 2639˘ 1± 1 Temperature at the MCr entrance/permeate side (°C) 26 ± 1

The composition of the components present in higher amounts in the RO brine considered in The composition of the components present in higher amounts in the RO brine considered in the the experiments is reported in Table4. In order to well compare the experimental results with the experiments is reported in Table 4. In order to well compare the experimental results with the simulations, the latter were repeated, considering the composition reported in Table4. simulations, the latter were repeated, considering the composition reported in Table 4.

Table 4. RO brine composition utilized in the experiments. Table 4. RO brine composition utilized in the experiments.

K (mol/L)K (mol/L) 0.0140.014 Na (mol/L)Na (mol/L) 0.660.66 MgMg (mol/L) (mol/L) 0.0730.073 Ca (mol/L)Ca (mol/L) 0.0140.014 Sr (mol/L) 0.0001 Cl (mol/L)Sr (mol/L) 0.00010.77 pHCl (mol/L) 0.777.98 pH 7.98 NaCl crystals were obtained at WRF of 87.8%, with CVs less than 38.6%. The produced crystals NaCl crystals were obtained at WRF of 87.8%, with CVs less than 38.6%. The produced crystals showed the characteristic cubic block-like form in accordance with the expected geometry of the NaCl showed the characteristic cubic block-like form in accordance with the expected geometry of the NaCl crystals when examined visually with optic microscope (Figure6). Low CV, like that achieved in MCr, crystals when examined visually with optic microscope (Figure 6). Low CV, like that achieved in is characteristic of a good product [25]. MCr, is characteristic of a good product [25].

Figure 6. NaCl crystalline habit. Picture from opticaloptical microscope, magniﬁcation:magnification: ˆ×10.10.

Good agreement between experimental tests and model (Figure 7), with deviations of only Good agreement between experimental tests and model (Figure7), with deviations of only 2.09%, 2.09%, can be observed. The reason for the slightly later start of precipitation in the experiments with can be observed. The reason for the slightly later start of precipitation in the experiments with respect respect to simulation is due to induction time. The comparison of simulation and experiments to simulation is due to induction time. The comparison of simulation and experiments conﬁrms the confirms the validity of the simulation study done and its suitability for a preliminary screening of validity of the simulation study done and its suitability for a preliminary screening of the potentialities the potentialities offered by membrane crystallization in the mining industry. offered by membrane crystallization in the mining industry. ] g] g k k Yield [ Yield [

Figure 7. Comparison of simulation and experimental results. The simulation is corresponding to the values in Table 4, initial volume of 1 L and temperature of 39 °C.

Crystals 2016, 6, 36 8 of 13

Table 3. Operating conditions used in the experiments.

Feed Flow Rate (L/h) 200 Permeate flow rate (L/h) 100 Temperature at the MCr entrance/feed side (°C) 39 ± 1 Temperature at the MCr entrance/permeate side (°C) 26 ± 1

The composition of the components present in higher amounts in the RO brine considered in the experiments is reported in Table 4. In order to well compare the experimental results with the simulations, the latter were repeated, considering the composition reported in Table 4.

Table 4. RO brine composition utilized in the experiments.

K (mol/L) 0.014 Na (mol/L) 0.66 Mg (mol/L) 0.073 Ca (mol/L) 0.014 Sr (mol/L) 0.0001 Cl (mol/L) 0.77 pH 7.98

NaCl crystals were obtained at WRF of 87.8%, with CVs less than 38.6%. The produced crystals showed the characteristic cubic block-like form in accordance with the expected geometry of the NaCl crystals when examined visually with optic microscope (Figure 6). Low CV, like that achieved in MCr, is characteristic of a good product [25].

Figure 6. NaCl crystalline habit. Picture from optical microscope, magnification: ×10.

Good agreement between experimental tests and model (Figure 7), with deviations of only 2.09%, can be observed. The reason for the slightly later start of precipitation in the experiments with respect to simulation is due to induction time. The comparison of simulation and experiments confirmsCrystals 2016 the, 6, 36validity of the simulation study done and its suitability for a preliminary screening9 of 13of the potentialities offered by membrane crystallization in the mining industry. ] g] g k k Yield [ Yield [

Figure 7. Comparison of simulation and experimental re results.sults. The simulation is corresponding to the ˝ values in Table4 4,, initialinitial volume volume of of 1 1 L L and and temperature temperature of of 39 39 °C.C.

3.3. Recovery from RO Brine Crystals 2016, 6, 36 9 of 13 The overall efficiency of an integrated membrane desalination plant with MCr treating the NF retentate3.3. Recovery and ROfrom brineRO Brine is reported in Figure8. Considering both the present thermodynamic simulationThe and overall the experimental efficiency of an results integrated from membra earlierne studiesdesalination [17 ,plant23,25 with,28], MCr it is treating assumed the NF that some ions (includingretentate barium,and RO brine strontium, is reported and magnesium)in Figure 8. Considering can be more both easily the present recovered thermodynamic from NF retentate. In casesimulation magnesium and will the experimental also be recovered results from earlie RO brine,r studies its [17,23,25,28], recovery will it is beassumed higher that than some the 66.2% ions (including barium, strontium, and magnesium) can be more easily recovered from NF retentate. (Figure8). Since sodium can be recovered from NF retentate and RO brine, its removal percentage from In case magnesium will also be recovered from RO brine, its recovery will be higher than the 66.2% seawater(Figure is near 8). toSince 100%. sodium NaCl can has be beenrecovered extensively from NF studiedretentate forand recovery RO brine, by its membraneremoval percentage crystallization from NFfrom retentate seawater and is ROnear brine, to 100%. and NaCl therefore has been the separationextensively hasstudied been for experimentally recovery by membrane verified (in the previouscrystallization section and from in literatureNF retentate [17 and,23 RO,25 brine,,28]). an Simulationsd therefore the indicate separation that has potassium been experimentally and nickel can also beverified recovered (in the from previous NF and section RO and brine in literature with a high [17,23,25,28]). percentage Simulations of recovery. indicate However, that potassium these results requireand experimental nickel can also validation. be recovered The from higher NF and amount RO brine of with monovalent a high percentage ions in of the recovery. RO brine However, with respect these results require experimental validation. The higher amount of monovalent ions in the RO brine to NF retentatewith respect indicates to NF retentate that 73.8% indicates of lithium that 73.8% can of belithium recovered. can be recovered. However, However, it should it should be noticed be that, since thenoticed curve that, of lithiumsince the precipitationcurve of lithium (Figure precipitation4) has (Figure not reached 4) has not steady reached state steady but state is still but increasingis still at the finalincreasing studied at water the final recovery studied factor,water recovery the amount factor, of the lithium amount recoveredof lithium recovered will be higherwill be higher at increasing water recovery.at increasing water recovery.

Figure 8.FigureTotal 8. Total amount amount of ionsof ions that that can can be be recoveredrecovered from from seawater seawater by means by means of MCr of at MCr a water at a water recoveryrecovery factor factor of 98.6%. of 98.6%.

Some of the ions shown in Table 2 have not been precipitated at an overall WRF of 98.6%. However, by evaluating the saturation index (SI), an improved understanding of the missing precipitation can be achieved. If the saturation index is negative, the minerals remain dissolved, whereas if it becomes positive, the minerals precipitate. For example, manganese and copper are near precipitation from NF retentate (Figure 9). Due to the higher concentration of chlorides, it is more likely to precipitate MnCl2 and CuCl2 with respect to sulfate compounds, for example. However, above a WRF of 97.5%, the SI starts to decrease, which can be related to the precipitation of other chloride compounds (Figure 3). In the treatment of RO brine, manganese is again close to precipitation. Eventually, membrane crystallization can be integrated with other unit operations (such as supported liquid membranes, etc.) in order to address the separation and recovery of these minerals from the highly concentrated solutions produced via membrane crystallizer.

Crystals 2016, 6, 36 10 of 13

Some of the ions shown in Table2 have not been precipitated at an overall WRF of 98.6%. However, by evaluating the saturation index (SI), an improved understanding of the missing precipitation can be achieved. If the saturation index is negative, the minerals remain dissolved, whereas if it becomes positive, the minerals precipitate. For example, manganese and copper are near precipitation from NF retentate (Figure9). Due to the higher concentration of chlorides, it is more likely to precipitate MnCl 2 and CuCl2 with respect to sulfate compounds, for example. However, above a WRF of 97.5%, the SI starts to decrease, which can be related to the precipitation of other chloride compounds (Figure3). In the treatment of RO brine, manganese is again close to precipitation. Eventually, membrane crystallization can be integrated with other unit operations (such as supported liquid membranes, etc.) in order to address the separation and recovery of these minerals from the highly concentrated solutions produced via membrane crystallizer. Crystals 2016, 6, 36 10 of 13

Figure 9. Saturation indicesindices (SI)(SI) ofof somesome of of the the compounds compounds which which have have not not yet yet been been precipitated precipitated at anat anoverall overall water water recovery recovery factor factor (NF+RO) (NF+RO) of 98.6%.of 98.6%.

Figure 10 shows the comparison of water consumption for minerals recovery through (1) the conventional miningmining industryindustry and and (2) (2) integrated integrated membrane membrane systems. systems. Water Water in mining in mining is used is used in a widein a widerange range of activities, of activities, such as such mineral as mineral processing, processing, dust suppression, dust suppression, slurry transport, slurry transport,etc. [34]. Mudd etc. [34]. [35] Muddmade a[35] preliminary made a preliminary study on embodied study on water embodied for different water materials for different coming materials from the coming mining from industry the miningwith data industry available with from data the available industry from itself. the The industry available itself. data The show available that the data embodied show that water the is embodiedvery high andwater with is very high high standard and with deviations high standard (as can deviations be observed (as in can the be case observed of nickel). in theThe case high of nickel).standard The deviation high standard is associated deviation with is associated the different with mining the different sites and mining the differencesites and the in oredifference grade, inopen ore cutgrade, mining open or cut underground mining or underground mining, mill mining, configuration mill configuration and design, and water design, quality, water project quality, age, projectclimate, age, and climate, length ofand slurry length pipelines, of slurry which pipelines, all affect which the all embodied affect the water embodied [35]. Althoughwater [35]. the Although mining theindustry mining has industry made many has made efforts many and improvedefforts and their improved water managementtheir water management significantly significantly by closed loop by closedwater circuits,loop water the watercircuits, requirements the water requirements are still very high.are still On very the contrary,high. On mineralsthe contrary, recovery minerals from recoverythe sea through from the integrated sea through membrane integrated systems membrane has the systems great advantage has the great that advantage water is produced that water and is producednot consumed. and Innot particular, consumed. the In amount particular, of water the producedamount of in anwater integrated produced NF/RO/MCr in an integrated system NF/RO/MCris much higher system than is themuch amount higher consumed than the amount by the consumed conventional by the mining conventional industry mining to recover industry one toton recover of nickel. one However,ton of nickel. high However, water production high water can production only be obtained can only because be obtained of the because low impact of the of lowconcentration impact of onconcentration MCr process on performance, MCr process andperformance, that it is possible and that to it avoid is possible scaling. to Dependingavoid scaling. on Dependingstream composition, on stream proper composition, pre-treatment proper and pr managemente-treatment ofand the management operative conditions of the operative allow the conditionscontrol and allow minimization the control of and scaling minimization and fouling, of scaling to promote and crystalsfouling, formationto promote in crystals the precipitation formation intank the and precipitation to avoid crystals tank and growth to avoid on membrane crystals growth surface on [17 membrane,23,25,28,36 surface]. From [17,23,25,28,36]. the precipitation From tank, the precipitation crystals can be tank, filtered the crystals and recovered. can be filtered This kind and ofrecovered. crystals recoveryThis kind system of crystals has recovery been developed system hasin the been study developed by Macedonio in theet study al. [36 by]. Macedonio Macedonioet et al. al.[28 [36].] have Macedonio previously et highlighted al. [28] have the previously economic highlightedperspective ofthe introducing economic perspective MCr in desalination. of introducing In fact, MCr due in todesalination. the potential In sale fact, of due salts to (inthe this potential study sale of salts (in this study NaCl and MgSO4·7H2O), the overall water production cost can be negative. Depending on if waste heat and energy recovery devices are available or not, the water production costs are found to be in the range of −0.49 to −0.71 $/m3 [28]. This emphasizes that MCr can prospectively be a very interesting technology for minerals recovery from desalination brine. Moreover, extending the number of salts to recover might also further enhance the economic benefits. Minerals recovery from the conventional mining industry and integrated membrane desalination systems could be compared also from an energetic point of view. Direct comparison of energy consumption in mining and integrated membrane systems is out of the scope of this paper. Nevertheless, it has to be mentioned that MCr, due to the low temperature, can utilize waste heat or other low-grade heat sources. This minimizes energy consumption. Integrated membrane-based desalination processes could have, in future, another advantage in addition to water and minerals production. In fact, many large-scale desalination projects are emphasizing on energy utilization by exploiting the mixing energy of high concentration and low concentration solutions, e.g., seawater and brine. From this perspective, future desalination plants

Crystals 2016, 6, 36 11 of 13

NaCl and MgSO4¨ 7H2O), the overall water production cost can be negative. Depending on if waste heat and energy recovery devices are available or not, the water production costs are found to be in the Crystals 2016, 6, 36 11 of 13 range of ´0.49 to ´0.71 $/m3 [28]. This emphasizes that MCr can prospectively be a very interesting cantechnology produce for water, minerals minerals, recovery and from optimize desalination the en brine.ergy demand, Moreover, thus extending further the reducing number the of saltsactual to negativerecover might impacts also of further mining enhance and desalination the economic industry. beneﬁts.

Figure 10. WaterWater consumption consumption for for minerals minerals recovery recovery in in the mining industry and for integrated membrane desalination system. Water consumption in the mining industry is adoptedadopted fromfrom [[35].35].

4. Conclusions Minerals recovery from the conventional mining industry and integrated membrane desalination systemsThis couldstudy beshows compared the potential also from of redesigning an energetic the point mining of view. industry Direct through comparison the adoption of energy of integratedconsumption membrane in mining systems. and integratedClearly, today membrane mining cannot systems be isreplaced out of completely the scope with of this recovery paper. fromNevertheless, desalination it has brine. to be However, mentioned due that to MCr, many due li tomits the of low the temperature, mining industry can utilize also in waste the heatfuture, or includingother low-grade water heatconsumption, sources. This renewable minimizes energy energy sources, consumption. and mineral depletion, the recourse to membraneIntegrated technology membrane-based can offer an desalinationinteresting perspective. processes could By means have, of in MCr, future, it is anotherpossible advantageto recover manyin addition different to waterions from and seawater. minerals Thanks production. to the Infractionation fact, many of large-scale ions by the desalination NF membrane, projects barium, are strontium,emphasizing and on magnesium energy utilization are easier by to exploiting recover from the mixingNF retentate energy with of high respect concentration to RO brine. and In this low study,concentration only one solutions, NF membrane e.g., seawater has been and considered brine. From, but this different perspective, ion rejection future desalination of other membranes plants can canproduce fractionate water, the minerals, ions further. and optimize Besides the NaCl, energy it can demand, also be thus possible further to reducingrecover KCl the and actual NiCl negative2 from theimpacts NF retentate, of mining but and also desalination from RO brine. industry. On the other hand, lithium can only be recovered from RO brine. Considering water consumption in the mining industry, an integrated membrane system will produce4. Conclusions a larger amount of water during the production of a similar amount of minerals. For 3 example,This the study conventional shows the mining potential industry of redesigning consumes the around mining 107 industry m of water through to recover the adoption one ton of 6 3 nickelintegrated (metal). membrane In the integrated systems. Clearly,membrane today system, mining it is cannot possible be replacedto produce completely 174 × 10 with·m water recovery per tonfrom nickel desalination (metal) brine.obtained However, (when duenickel to is many recovered limits ofboth the from mining NF industry retentate also and in RO the brine), future, highlightingincluding water the advantages consumption, of combining renewable mineral energy and sources, water and production. mineral Furthermore, depletion, the in recourse the future, to energymembrane production technology might can also offer be an introduced interesting in perspective. desalination, By making means of minerals MCr, it isrecovery possible even to recover more economicalmany different and ions sustainably from seawater. feasible. Thanks to the fractionation of ions by the NF membrane, barium, Authorstrontium, Contributions: and magnesium Cejna Anna are easier Quist-Jensen to recover and from Francesca NF retentate Macedonio with performed respect to the RO thermodynamic brine. In this analysisstudy, only and the one experimental NF membrane work, has respectively. been considered, Cejna Anna but Quist-Jensen different ion and rejection Francesca of Macedonio other membranes wrote the manuscriptcan fractionate in collaboration. the ions further.Enrico Drioli Besides initiated NaCl, and itsupervised can also the be work possible and revised to recover the manuscript. KCl and NiCl 2 Conflictsfrom the of NF Interest: retentate, The authors but also declare from no RO conflict brine. of On interest. the other hand, lithium can only be recovered from RO brine. Considering water consumption in the mining industry, an integrated membrane Referencessystem will produce a larger amount of water during the production of a similar amount of minerals. For example, the conventional mining industry consumes around 107 m3 of water to recover one 1. World Health Organization (WHO). Driking-Water, Fact sheet N°391. Available online: ton of nickel (metal). In the integrated membrane system, it is possible to produce 174 ˆ 106¨ m3 http://www.who.int/mediacentre/factsheets/fs391/en/ (accessed on 5 August 2015). water per ton nickel (metal) obtained (when nickel is recovered both from NF retentate and RO brine), 2. Rühl, C.; Appleby, P.; Fennema, J.; Naumov. A.; Schaffer, M. Economic Development and the Demand for Energy: A Historical Perspective on the Next 20 Years. Energy Policy 2012, 50, 109–116. 3. Drioli, E.; Giorno, L. Comprehensive Membrane Science and Engineering; Elsevier: Amsterdam, The Netherlands, 2010.

Crystals 2016, 6, 36 12 of 13 highlighting the advantages of combining mineral and water production. Furthermore, in the future, energy production might also be introduced in desalination, making minerals recovery even more economical and sustainably feasible.

Author Contributions: Cejna Anna Quist-Jensen and Francesca Macedonio performed the thermodynamic analysis and the experimental work, respectively. Cejna Anna Quist-Jensen and Francesca Macedonio wrote the manuscript in collaboration. Enrico Drioli initiated and supervised the work and revised the manuscript.

Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. World Health Organization (WHO). Driking-Water, Fact sheet N˝391. Available online: http://www.who.int/mediacentre/factsheets/fs391/en/ (accessed on 5 August 2015). 2. Rühl, C.; Appleby, P.; Fennema, J.; Naumov, A.; Schaffer, M. Economic Development and the Demand for Energy: A Historical Perspective on the Next 20 Years. Energy Policy 2012, 50, 109–116. [CrossRef] 3. Drioli, E.; Giorno, L. Comprehensive Membrane Science and Engineering; Elsevier: Amsterdam, The Netherlands, 2010. 4. Charpentier, J-C. Among the Trends for a Modern Chemical Engineering, the Third Paradigm: The Time and Length Multiscale Approach as an Efficient Tool for Process Intensification and Product Design and Engineering. Chem. Eng. Res. Des. 2010, 88, 248–254. [CrossRef] 5. Drioli, E.; Stankiewicz, A.I.; Macedonio, F. Membrane Engineering in Process Intensification—An Overview. J. Memb. Sci. 2011, 380, 1–8. [CrossRef] 6. Macedonio, F.; Drioli, E.; Gusev, A.A.; Bardow, A.; Semiat, R.; Kurihara, M. Efficient Technologies for Worldwide Clean Water Supply. Chem. Eng. Process. Process Intensif. 2012, 51, 2–17. [CrossRef] 7. Drioli, E.; Brunetti, A.; Di Profio, G.; Barbieri, G. Process Intensification Strategies and Membrane Engineering. Green Chem. 2012, 14, 1561–1572. [CrossRef] 8. Global Water Intelligence. IDA Desalination Yearbook 2011–2012; Media Analytics Ltd.: Oxford, UK, 2013. 9. UNESCO Centre for Membrane Science and Technology University of New South Wales. Emerging Trends in Desalination: A Review; National Water Commision: Canberra, Australia, 2008. 10. Drioli, E.; Criscuoli, A.; Macedonio, F. Membrane Based Desalination: An Integrated Approach (Medina) (European Water Research); IWA Publishing: London, UK, 2011. 11. Kim, S.; Oh, B.S.; Hwang, M-H.; Hong, S.; Kim, J-H.; Lee, S.; Kim, I.S. An Ambitious Step to the Future Desalination Technology: SEAHERO R&D Program (2007–2012). Appl. Water Sci. 2011, 1, 11–17. 12. Kurihara, M.; Hanakawa, M. Mega-ton Water System: Japanese National Research and Development Project on Seawater Desalination and Wastewater Reclamation. Desalination 2013, 308, 131–137. [CrossRef] 13. Kim, S-H.; Kim, D-I. Scaling-up and Piloting of Pressure-retarded Osmosis. Desalin. Water Reuse. 2014, 24, 36–38. 14. Drioli, E.; Ali, A.; Macedonio, F. Membrane Distillation: Recent Developments and Perspectives. Desalination 2015, 356, 56–84. [CrossRef] 15. Ali, A.; Macedonio, F.; Drioli, E.; Aljlil, S.; Alharbi, O.A. Experimental and Theoretical Evaluation of Temperature Polarization Phenomenon in Direct Contact Membrane Distillation. Chem. Eng. Res. Des. 2013, 91, 1966–1977. [CrossRef] 16. Curcio, E.; Drioli, E. Membrane Distillation and Related Operations—A Review. Separat. Purifi. Rev. 2005, 34, 35–86. [CrossRef] 17. Macedonio, F.; Quist-Jensen, C.A.; Al-Harbi, O.; Alromaih, H.; Al-Jlil, S.A.; Al Shabouna, F.; Drioli, E. Thermodynamic Modeling of Brine and its Use in Membrane Crystallizer. Desalination 2013, 323, 83–92. [CrossRef] 18. Parkhurst, D.L.; Appelo, C.A. Description of Input and Examples for PHREEQC Version 3—A Computer Program for Speciation, Batch-Reaction, One-Dimensional Transport, and Inverse Geochemical Calculations. Available online: http://pubs.usgs.gov/tm/06/a43 (accessed on 17 July 2014). 19. Bardi, U. Extracting Minerals from Seawater: An Energy Analysis. Sustainability 2010, 2, 980–992. [CrossRef] Crystals 2016, 6, 36 13 of 13

20. Macedonio, F.; Quist-Jensen, C.A.; Drioli, E. Raw Materials Recovery from Seawater for Zero Liquid Discharge. In Proceedings of The International Desalination Association World Congress on Desalination and Water Reuse 2015, San Diego, CA, USA, 30 August–4 September 2015. 21. Tainter, J.A.; Patzek, TW. Offshore Drilling and Production: A Short History. In Drilling Down; Springer: New York, NY, USA, 2012; pp. 53–63. 22. U.S. Geological Survey. Minerals Information: Mineral Commodity Summaries 2014. Available online: http://minerals.usgs.gov/minerals/pubs/mcs/2014/mcs2014.pdf (accessed on 25 March 2015). 23. Quist-Jensen, C.A.; Macedonio, F.; Drioli, E. Membrane Crystallization for Salts Recovery from Brine—An Experimental and Theoretical Analysis. Desalin. Water Treat. 2015, 57, 7593–7603. [CrossRef]

24. Drioli, E.; Curcio, E.; Criscuoli, A.; Di Profio, G. Integrated System for Recovery of CaCO3, NaCl and MgSO4¨ 7H2O from Nanofiltration Retentate. J. Memb. Sci. 2004, 239, 27–38. [CrossRef] 25. Macedonio, F.; Drioli, E. Hydrophobic Membranes for Salts Recovery from Desalination Plants. Desalin. Water Treat. 2010, 18, 224–234. [CrossRef] 26. Di Profio, G.; Tucci, S.; Curcio, E.; Drioli, E. Controlling Polymorphism with Membrane-Based Crystallizers: Application to Form I and II of Paracetamol. Chem. Mater. 2007, 19, 2386–2388. [CrossRef] 27. Di Profio, G.; Curcio, E.; Ferraro, S.; Stabile, C.; Drioli, E. Effect of Supersaturation Control and Heterogeneous Nucleation on Porous Membrane Surfaces in the Crystallization of L-Glutamic Acid Polymorphs. Cryst. Growth Des. 2009, 9, 2179–2186. [CrossRef] 28. Macedonio, F.; Curcio, E.; Drioli, E. Integrated Membrane Systems for Seawater Desalination: Energetic and Exergetic Analysis, Economic Evaluation, Experimental Study. Desalination. 2007, 203, 260–276. [CrossRef] 29. Mohr, S.H.; Mudd, G.; Giurco, D. Lithium Resources and Production: Critical Assessment and Global Projections. Minerals 2012, 2, 65–84. [CrossRef] 30. Gruber, P.W.; Medina, P.A.; Keoleian, G.A.; Kesler, S.E.; Everson, M.P.; Wallington, T.J. Global Lithium Availability—A Constraint for Electric Vehicles? J. Ind. Ecol. 2011, 15, 760–775. [CrossRef] 31. Grosjean, C.; Miranda, P.H.; Perrin, M.; Poggi, P. Assessment of World Lithium Resources and Consequences of Their Geographic Distribution on the Expected Development of the Electric Vehicle Industry. Renew. Sustain. Energy Rev. 2012, 16, 1735–1744. [CrossRef] 32. Kesler, S.E.; Gruber, P.W.; Medina, P.A.; Keoleian, G.A.; Everson, M.P.; Wallington, T.J. Global Lithium Resources: Relative Importance of Pegmatite, Brine and Other Deposits. Ore. Geol. Rev. 2012, 48, 55–69. [CrossRef] 33. Quist-Jensen, C.A.; Ali, A.; Mondal, S.; Macedonio, F.; Drioli, E. A Study of Membrane Distillation and Crystallization for Lithium Recovery from High Concentrated Aqueous Solutions. J. Memb. Sci. 2016, 505, 167–173. [CrossRef] 34. International Council of Mining & Metals. Water Management in Mining: A Selection of Case Studies; International Council of Mining & Metals: London, UK, 2012. 35. Mudd, G.M. Sustainability Reporting and Water Resources: A Preliminary Assessment of Embodied Water and Sustainable Mining. Mine Water Environ. 2008, 27, 136–144. [CrossRef] 36. Macedonio, F.; Drioli, E.; Curcio, E.; Di Profio, G. Experimental and Economical Evaluation of a Membrane Crystallizer Plant. Desalin Water Treat. 2009, 9, 49–53. [CrossRef]

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