Arsenic Removal by Coagulation With Aluminum, Iron, Titanium, and Zirconium

Arsenite [As(III)] and arsenate [As(V)] removal using zirconium and titanium coagulants was compared with removal using ferric chloride (FeCl3) and alum in a standard challenge water. As(III) adsorption was significantly lower than As(V) adsorption at all pH levels with all coagulants. The highest As(V) loadings both on mass and molar bases were observed with FeCl3. As(V) removal increased with decreasing pH with all coagulants. The small amount of As(III) removal observed was generally independent of pH. Alum did not remove any As(III). The highest As(III) loadings were observed with titanium(III) [Ti(III)], which appeared to be oxidized to As(V) by peroxide resulting from Ti(III) hydrolysis. The types of sludge produced by all coagulants passed the toxicity characteristic leaching procedure and the waste extraction test. When chemical costs were compared, FeCl3 was the most cost‐effective coagulant for As(III) and As(V) at all three pH values, and As(III) chemical coagulation costs were five to 20 times higher than those for As(V). Alum was four to eight times the cost of FeCl3 for As(V) removal.