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Removal of Hazardous Oxyanions from the Environment Using Metal-Oxide-Based Materials

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materials Review Removal of Hazardous Oxyanions from the Environment Using Metal-Oxide-Based Materials Ewelina Weidner and Filip Ciesielczyk * Institute of Chemical Technology and Engineering, Faculty of Chemical Technology, Poznan University of Technology, Berdychowo 4, PL-60965 Poznan, Poland; [email protected] * Correspondence: fi[email protected]; Tel.: +48-61-6653626 Received: 11 February 2019; Accepted: 14 March 2019; Published: 20 March 2019 Abstract: Scientific development has increased the awareness of water pollutant forms and has reawakened the need for its effective purification. Oxyanions are created by a variety of redox-sensitive metals and metalloids. These species are harmful to living matter due to their toxicity, nondegradibility, and mobility in aquatic environments. Among a variety of water treatment techniques, adsorption is one of the simplest, cheapest, and most effective. Since metal-oxide-based adsorbents poses a variety of functional groups onto their surface, they were widely applied in ions sorption. In this paper adsorption of harmful oxyanions by metal oxide-based materials according to literature survey was studied. Characteristic of oxyanions originating from As, V, B, W and Mo, their probable adsorption mechanisms and comparison of their sorption affinity for metal-oxide-based materials such as iron oxides, aluminum oxides, titanium dioxide, manganium dioxide, and various oxide minerals and their combinations are presented in this paper. Keywords: oxyanions; sorption; metal oxides; environment pollution; water purification; adsorbents; hazardous metals 1. Introduction Intensive industrial development has contributed to the increased pollution of the environment with hazardous metals and metalloids. The majority of these elements are redox sensitive and some of their oxidation states can form oxyanions in solution. Oxyanions (or oxoanions) are polyatomic z− negatively charged ions containing oxygen with the generic formula AxOy (where A represents a chemical element and O represents an oxygen atom) [1]. Those compounds represent a range of different species depending both on pH and redox potential [2]. Oxyanions of As, V, B, W, and Mo are commonly found trace pollutants in various waste streams [1,3]. Metal(loid) oxyanions are characterized by toxicity [4–6], nonbiodegradability [5,6], and high solubility in water [7], which makes them extremely mobile harmful species which easily bioaccumulate in the environment and in the food chain [8]. Thus these species are very dangerous even at low concentrations. They can be transferred into living organisms via inhalation, ingestion, and skin adsorption, causing irreversible effects [5]. The main sources of hazardous oxyanions are alkaline wastes originating from high temperature processes with the thermal treatment of waste, fossil fuel combustion, and ferrous or non-ferrous metal smelting [2], nonetheless they are also produced in microelectronics, electroplating, metal finishing, battery manufacturing, tannery, metallurgy, and fertilizer industries [5]. However industrial activities are significantly increasing the concentration of oxyanions, and there are environments where geological formations promote dissolution of weak-acid oxyanion species, like arsenic, vanadium, or antimony, which pollute ground water sources used by local communities [9]. Considering the harmful properties of metal(loid) oxyanions, their effective elimination from water and wastewater is becoming a key issue for environment and public health protection. Nonetheless in comparison Materials 2019, 12, 927; doi:10.3390/ma12060927 www.mdpi.com/journal/materials Materials 2019, 12, x FOR PEER REVIEW 2 of 34 MaterialsMaterials2019 2019, 12, 12, 927, x FOR PEER REVIEW 2 of2 of34 32 protection. Nonetheless in comparison with research concerning cationic pollutants, number of protection. Nonetheless in comparison with research concerning cationic pollutants, number of withworks research pertained concerning to oxyanions cationic removal pollutants, is still number dramatically of works pertainedlow, what to can oxyanions be seen removal on the ischart still works pertained to oxyanions removal is still dramatically low, what can be seen on the chart dramaticallypresented in low,Figure what 1. can be seen on the chart presented in Figure1. presented in Figure 1. oxyanions cationscations anionsanions 700700 600600 500500 400400 300300 Number of papers of Number Number of papers of Number 200200 100100 00 FigureFigureFigure 1. 1.1. BarBar chartchart ofof thethethe numbernumber ofof articlesarticles perper yearyear concerning concerning cations, cations,cations, anions anionsanions and andand oxyanions oxyanionsoxyanions adsorptionadsorptionadsorption forfor for thethe the 1989–28 1989–281989–28 JanuaryJanuary 2019.2019. TheThe statistical statistical data datadata were werewere obtained obtainedobtained by byby searching searchingsearching “adsorption “adsorption“adsorption metalmetalmetal oxideoxide oxide cations/anions/oxyanions”cations/anions/oxyanions” cations/anions/oxyanions” phrases phrases inin in thethe the Scopus Scopus Scopus data data data base base base as as as title title title and and and keywords. keywords. keywords. TheTheThe removalremoval removal ofof of thosethose those hazardous hazardoushazardous speciesspecies fromfrom wastwastewaterwastewaterewater and andand water waterwater sources sourcessources have havehave been beenbeen subjected subjectedsubjected tototo a a varietya varietyvariety of techniquesofof techniquestechniques e.g., ione.g.,e.g., exchange, ion exchange, filtration, filtration,filtration, adsorption, adsorption,adsorption, reverse osmosis,reversereverse osmosis, solventosmosis, extraction, solvent solvent chemicalextraction,extraction, precipitation, chemicalchemical precipitation,precipitation, evaporation evaporation and concentration, anandd concentration,concentration, electrodialysis, electrodialysis, electrodialysis, and biomethods and and biomethods biomethods [10–13 ]. The[10–13].[10–13]. main The The methods main main methodsmethods used for usedused wastewater for wastewater treatment treatmenttreatment with particular with with particular particular regard regard regard to adsorption to to adsorption adsorption has has been has been shown in Figure 2. shownbeen shown in Figure in Figure2. 2. Figure 2. Methods of wastewater treatment. FigureFigure 2.2. MethodsMethods ofof wastewaterwastewater treatment.treatment. The main problem with the majority of those methods is their high cost and need for advanced equipment.TheThe mainmain Adsorption problemproblem with withis in thethe majoritymajorityadvantage ofof over thosethose other methodsmethods techniques isis theirtheir in highhigh water costcost treatment andand needneed due forfor to advancedadvanced its low equipment.equipment.cost, simple Adsorption design, easy is operation, in thethe advantageadvantage insensitivity over to other toxic techniquesspecies, no secondary in water treatmenttreatment pollutants due production toto itsits lowlow cost,cost,and simple simplehigh efficiency design,design, easyeasy [14]. operation,operation, Many adsorbents insensitivityinsensitivity have to tobe toxictoxicen proposed species,species, noinno literature secondarysecondary for pollutantspollutants water purification productionproduction andandfrom highhigh harmful efficiency efficiency oxyanion [14 [14].]. Manyspecies, Many adsorbents includingadsorbents haveactivated have been be ca proposedenrbons proposed [15,16], in literature in lignocellulosic literature for water for materials water purification purification [8], gold from harmfulfrom[17,18], harmful oxyanionsilver oxyanion [19], species, zero species, valent including iron including activated[20], natural activated carbons minerals ca [15rbons,16 like], [15,16], lignocellulosic zeolites lignocellulosic [21–24], materials calcite materials [25], [8], gold bentonite [8], [17 gold,18 ], [17,18], silver [19], zero valent iron [20], natural minerals like zeolites [21–24], calcite [25], bentonite Materials 2019, 12, 927 3 of 32 silver [19], zero valent iron [20], natural minerals like zeolites [21–24], calcite [25], bentonite [14], goethite [5,26–30], kaolinite [31], graphene oxide [32], metal hydroxides, or metal oxides. Metal oxides are characterized by the presence of different types of surface groups [33]. Thus metal-oxide-based materials reveal a capability to adsorb ions [34] and because of that one of their major uses is for adsorbing metal or nonmetal ions from aqueous wastewater streams [35]. In this work adsorption of harmful oxyanions by metal oxide-based materials according to a literature survey have been studied. 2. Arsenic Oxyanions 2.1. Arsenic Pollution Arsenic is a metalloid that occurs in in the +III and +V oxidation states. It is a building element of the Earth’s crust and is naturally occurring in the environment in the air, soils and rocks, natural water, and organisms [36,37]. In its inorganic form it is strongly carcinogenic and highly toxic. Nowadays arsenic pollution has been recognized to be one of the world’s greatest environmental hazards. The World Health Organization consider it one of the top ten major public health concern chemicals. The United States Environmental Protection Agency have located inorganic compounds of arsenic like arsenic acid, arsenic(III) oxide, and arsenic(V) oxide on the hazardous waste list [38]. The International Agency for Research on Cancer has
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