Removal of Heavy Metal Ions from Water and Wastewaters by Sulfur-Containing Precipitation Agents
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Water Air Soil Pollut (2020) 231: 503 https://doi.org/10.1007/s11270-020-04863-w Removal of Heavy Metal Ions from Water and Wastewaters by Sulfur-Containing Precipitation Agents Alina Pohl Received: 6 March 2020 /Accepted: 14 September 2020 /Published online: 28 September 2020 # The Author(s) 2020 Abstract Restrictive requirements for maximum con- precipitation is obtained by using a higher dose of pre- centrations of metals introduced into the environment cipitating agent. However, toxic byproducts are often lead to search for effective methods of their removal. produced. It is required that the precipitation agents not Chemical precipitation using hydroxides or sulfides is only effectively remove metal ions from the solution but one of the most commonly used methods for removing also effectively bind with dyes or metal complexes. metals from water and wastewater. The process is simple and inexpensive. However, during metal hydroxide pre- . cipitation, large amounts of solids are formed. As a result, Keywords Metal sulfide precipitation Chelating . metal hydroxide is getting amphoteric and it can go back agents Dithiocarbamate compounds Asynthetic into the solution. On the other hand, use of sulfides is chelating ligand characterized by lower solubility compared with that of metal hydroxides, so a higherdegreeofmetalreduction can be achieved in a shorter time. Disadvantages of that 1Introduction process are very low solubility of metal sulfides, highly sensitive process to the dosing of the precipitation agent, As civilization develops, the level of environmental and the risks of emission of toxic hydrogen sulfide. All pollution with heavy metals intensifies. This pollution these restrictions forced to search for new and effective has an influence on air, water, and soil contamination by precipitants. Potassium/sodium thiocarbonate (STC) and dust, industrial gases, sewage, waste, and coal combus- 2,4,6-trimercaptotiazine (TMT) are widely used. Dithio- tion products containing heavy metals (Nocoń et al. carbamate (DTC) compounds are also used, e.g., sodium 2006; Barbusiński and Nocoń 2011). The persistent dimethyldithiocarbamate (SDTC), and ligands for perma- nature of these non-biodegradable pollutants is very nent metal binding, e.g., 1,3-benzenediamidoethanethiol dangerous. They tend to accumulate in living organ- (BDETH ), 2,6-pyridinediamidoethanethiol (PyDET), a 2 isms. After entering the food chain, they undergo pyridine-based thiol ligand(DTPY)orligandswithopen biomagnification processes and finally accumulate in chains containing many sulfur atoms, using of a tetrahe- the human body. Heavy metals are classified as sub- dral bonding arrangement around a central metal atom. stances that pose a particular threat to human health due The possibility of improving the efficiency of metal to their possible toxic or carcinogenic effects (Barakat 2011; Fu and Wang 2011). A. Pohl (*) As a result of many industrial processes, sewage is Institute of Environmental Engineering, Polish Academy of generated, and it contains a number of heavy metals, Sciences in Zabrze, M. Skłodowskiej-Curie 34 Street, 41-819 Zabrze, Poland such as zinc, copper, nickel, mercury, cadmium, lead, or e-mail: [email protected] chromium (Fu and Wang 2011). 503 Page 2 of 17 Water Air Soil Pollut (2020) 231: 503 Metals in wastewater can come from fertilizers or considered the most effective, occurs at a pH value of pesticides as well as from the plating, tanning, dyeing, < 6.5, which in practice means the acidification of the textile, or electrochemical industries (Koc-Jurczyk medium to be purified before the coagulation stage 2013). The most commonly used methods of metal (Mroczko and Zimoch 2018). removal from wastewater include methods based on Effectiveness of the chemical precipitation is also the precipitation of metal hydroxides or sulfides, ion affected by the type and concentration of metal ions exchange on chelating ion exchangers, evaporation in present in the solution, precipitation reagent used, reac- vacuum evaporators, reverse osmosis process, mem- tion conditions, and presence of other compounds that brane filtration, electrochemical processing technolo- can inhibit the reaction. The quantities of necessary gies, adsorption on various materials, co-precipitation chemicals used in the process are difficult to calculate. with ferrite, or the use of starch or borohydride xanthates It depends on the pH and alkalinity of the wastewater, to reduce metal ions to metallic form (Fu et al. 2006a; phosphate level, point of injection and mixing modes, Barakat 2011; Thomas et al. 2014). among other factors (Barakat 2011, US Environmental The scope of this work is to set the methods for Protection Agency (US EPA) 2000). In practice, the removing metals from water and wastewater, comparing metal precipitation does not coincide with the theoretical their effectiveness with particular emphasis on methods characteristics of their solubility and pH range specified based on sulfidation. for solutions containing single metal cations (Grabas 2009). Accurate doses should be determined by jar tests and confirmed by field evaluations. In wastewater treat- 2MethodsforRemovingMetalsfromWastewater ment, the most commonly used are: and Water-Chemical Precipitation – Lime - calcium oxide, CaO; Precipitation is a method in which contaminants (in dis- – Ferrous sulfate, Fe(SO4)3; solved or suspended form) are separated from the solution – Alum or filter alum, Al2(SO4)3∙14H2O; as a sediment, which can then be filtered, centrifuged, or – Ferric chloride, FeCl3; otherwise separated from the liquid part (US Environmen- – Polymer (US Environmental Protection Agency tal Protection Agency (US EPA) 2000, Fu and Wang (US EPA) 2000). 2011). The precipitate forms as a result of the formation of a complex between the precipitation agent and heavy In the coagulation process, traditional hydrolyzing metal ions, which reduces the bioavailability of metals aluminum salts such as aluminum sulfate or aluminum (Sheoran and Sheoran 2006). chloride are often used. Replacing them with new coag- Chemical precipitation is an effective and widely ulant generation, represented by pre-hydrolyzed alumi- used process in the industry. It is characterized by sim- num salts with a high degree of polymerization with the plicity and it is inexpensive to operate. It can be used to general formula Aln(OH)mCl3n − m, allows not only for remove pollutants from municipal and industrial waste- more efficient treatment but also to minimize the unde- water. It can also be used for water softening, heavy sirable effects of chemical dosing and higher efficiency metal removal from metal plating wastes, oil and grease over a wide range of pH and temperature (Mroczko and removal from emulsified solutions, and phosphate re- Zimoch 2018). As pre-hydrolyzed coagulants, moval from wash-waters and other wastewater (US polyaluminium chloride, sulfate (VI) polyaluminium, Environmental Protection Agency (US EPA) 2000,Fu and poly iron (III) may be mentioned (Nawrocki and and Wang 2011). In the technological system, the ob- Biłozor 2010;Krupińska 2011). tained precipitate is separated from the solution by sed- Conventional chemical precipitation methods in- imentation or filtration, and the treated water is then clude hydroxide precipitation and sulfide precipitation. decanted and respectively discharged or re-used (Fig. 1) (Fu and Wang 2011). One of the most important parameters regulating 3 Metal Hydroxide Precipitation chemical precipitation is pH. For the coagulation pro- cess, pH is a critical parameter. Generation of polymeric In a process of metal precipitation as hydroxides, an coagulant forms with a highly positive charge, alkaline agent is used, which raises the pH of the Water Air Soil Pollut (2020) 231: 503 Page 3 of 17 503 Fig. 1 Processes of a pH Coagulant addition e.g. conventional metals precipitation regulation FeSO4, FeCl3 treatment plant (Wang et al. 2004) Wastewater Sedimentation source pH regulation Solids Water Dewatering Filter Outflow Water Recirculation Disposal of sludge solution, resulting in a decrease of the metal ion solu- 4 Metal Sulfide Precipitation bility, and thus their precipitation from the solvent. For this purpose, lime or sodium hydroxide is most often Metal sulfide precipitation is also an effective method used. The mechanism of heavy metal removal by pre- for removing heavy metal ions. One of the main advan- cipitation of metal hydroxides is shown in Eq. 1: tages of using sulfides is the lower solubility of metal compounds than hydroxide precipitates (Table 1) (Wang et al. 2004;Lewis2010; Fu and Wang 2011; Bejan and Bunce 2015; Malik et al. 2019). 2þ þ ðÞ−↔ ðÞ ð Þ M 2OH MOH2 1 Sulfide precipitates are not amphoteric so it can achieve a high degree of metal removal in a shorter time over a wide pH range compared with hydroxide precip- itation. Precipitated sludge has better settling properties; where M2+ and OH− represent the dissolved metal ions it is easier to thicken and dewater compared with sludge and the precipitant, respectively, while M(OH)2 is the insoluble metal hydroxide (Wang et al. 2004). For the precipitation of heavy metals from the solu- Table 1 Theoretical solubilities of hydroxides and sulfides of tion, calcium carbonate, calcium hydroxide (slaked selected metals in pure water (Wang et al. 2004) lime), calcium oxide (quicklime), sodium carbonate (so- Metal Solubility of metal ion (mg/L) da ash), sodium hydroxide, and ammonium hydroxide can be used (Skousen et al. 2000;EgieborandOni2007; As hydroxide As sulfide Zhuang 2009; Maila et al. 2014; Skousen 2014). − − Process of metal hydroxide precipitation has many Cadmium (Cd2+)2.3∙ 10 5 6.7 ∙ 10 10 − advantages. It is a relatively simple technique, imple- Chrome (Cr3+)8.4∙ 10 4 No precipitate − − mentation costs are low, and its pH is easy to control. Cobalt (Co2+)2.2∙ 10 1 1.0 ∙ 10 8 Although, the process generates large volumes of low- Copper (Cu2+)2.2∙10−2 5.8 ∙ 10−13 density sludge that is difficult to further undergo Iron (Fe2+)8.9∙ 10−1 3.4 ∙ 10−5 dewatering (Menezes et al. 2010;Parketal.2013; Lead (Pb2+) 2.1 3.8 ∙ 10−9 Chen et al. 2014; Kim et al.