Editing Arsenic (section)

=== Arsenic removal ===

[[Coagulation (water treatment)|Coagulation]] and [[flocculation]] are closely related processes common in arsenate removal from water. Due to the net negative charge carried by arsenate ions, they settle slowly or not at all due to charge repulsion. In coagulation, a positively charged coagulent such as iron and aluminum (commonly used salts: FeCl<sub>3</sub>,<ref name="Bina 2013 17">{{cite journal |last1=Hesami |first1=Farid |last2=Bina |first2=Bijan |last3=Ebrahimi |first3=Afshin |last4=Amin |first4=MohammadMehdi |title=Arsenic removal by coagulation using ferric chloride and chitosan from water |journal=International Journal of Environmental Health Engineering |date=2013 |volume=2 |issue=1 |pages=17 |doi=10.4103/2277-9183.110170 |doi-access=free }}</ref> Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>,<ref>{{cite journal |last1=Sun |first1=Yuankui |last2=Zhou |first2=Gongming |last3=Xiong |first3=Xinmei |last4=Guan |first4=Xiaohong |last5=Li |first5=Lina |last6=Bao |first6=Hongliang |title=Enhanced arsenite removal from water by Ti(SO4)2 coagulation |journal=Water Research |date=September 2013 |volume=47 |issue=13 |pages=4340–4348 |doi=10.1016/j.watres.2013.05.028 |pmid=23764585 |bibcode=2013WatRe..47.4340S }}</ref> Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub><ref>{{cite journal |last1=Hering |first1=Janet G. |last2=Chen |first2=Pen-Yuan |last3=Wilkie |first3=Jennifer A. |last4=Elimelech |first4=Menachem |title=Arsenic Removal from Drinking Water during Coagulation |journal=Journal of Environmental Engineering |date=August 1997 |volume=123 |issue=8 |pages=800–807 |doi=10.1061/(ASCE)0733-9372(1997)123:8(800) }}</ref>) neutralize the negatively charged arsenate, enable it to settle. Flocculation follows where a flocculant bridges smaller particles and allows the aggregate to precipitate out from water. However, such methods may not be efficient on arsenite as As(III) exists in uncharged arsenious acid, H<sub>3</sub>AsO<sub>3</sub>, at near-neutral pH.<ref>{{cite journal |last1=Ng |first1=Wenfa |title=Inability to Completely Remove Trace Contaminants from Drinking Water by Adsorption |journal=Journal of Environmental Science and Public Health |date=9 March 2022 |volume=6 |issue=1 |pages=129–134 |url=https://fortuneonline.org/articles/inability-to-completely-remove-trace-contaminants-from-drinking-water-by-adsorption.html }}</ref>

The major drawbacks of coagulation and flocculation are the costly disposal of arsenate-concentrated sludge, and possible [[secondary contamination]] of environment. Moreover, coagulents such as iron may produce ion contamination that exceeds safety levels.<ref name="Bina 2013 17"/>