Arsenic(â…¢) Removal From Water By Ferric Coagulation Enhanced With Ferrate

Arsenic contamination is a worldwide problem. Many countries and regions have met the problem of arsenic contamination in drinking water. Long-term water-drinking with high concentration of arsenic can damage skin, liver, kidney, nervous system and reproductive system. Studies show that arsenic has carcinogenicity, teratogenicity and mutagenicity. The species of arsenic exist in arsenite and arsenate in natural water. Compared with As(V), As(III) is more toxic and instable, furthermore, As(III) can only very slowly be oxidized to As(V)in the natural conditions. Therefore, it is effective to pre-oxidize As(III) for enhancing the removal of arsenic.In this Study, As(III) was oxidized to As(V) by K₂FeO₄, then was coagulated and removed by FeCl3. Effect of parameters, such as Fe(III) dosage, Fe(VI) dosage, oxidation time and pH, flocculation pH, and hardness, humic acid, on As removal were investigated.Results show that K₂FeO₄ pre-oxidation increased the As removal and saved the total iron dosage. With a total iron dosage of 16.4mg/L (2.4mg/L Fe(VI)+14mg/L Fe(III)), residual As concentration in the treated water met the Standards for Drinking Water Quality of China (<0.01mg/L). The suitable oxidation time was 2min; the oxidation pH has no significant influence with a wide pH range: 4.0～9.0; the suitable flocculation pH was 6.0～8.5. Hardness has no significant influence on As removal, while humic acid has somewhat adverse influence. Increas of Fe(III) dosage can reduce the impact of humic acid. Turbidity-contributing materials have adverse influence on As removal. Existence of suitable quantity of turbidity-contributing materials can improve As removal. In conclusion, ferric coagulation enhanced with ferrate pre-oxidation can efficiently remove As from the source water.