US EPA

1378263 

Journal Article 

Arsenic immobilization by calcium arsenate formation 

Bothe J V, , JR; Brown, PW 

1999 

1 

Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 

BIOSIS/00/04017 

33 

21 

3806-3811 

eng 

BIOSIS COPYRIGHT: BIOL ABS. Lime additions to arsenic-containing wastes have been proven to be beneficial in reducing the mobility of dissolved arsenic, presumably through the formation of low-solubility calcium arsenates. However, the role of calcium arsenate formation in reducing the concentrations of dissolved arsenic has not been well established. Therefore, slurries with varying Cas ratios were equilibrated, and the compounds that formed at elevated pH values were established. In contrast to the literature, Ca3(AsO4)2 was not observed, rather Ca4(OH)2(AsO4)2 4H2O, Ca5(AsO4)3-OH (arsenate apatite), and Ca3(AsO4)2 32/3H2O had formed. The equilibrium concentrations of arsenic were found to be the lowest at high pH. Minimum arsenic concentrations in equilibrium with Ca4(OH)2(AsO4)2 4H2O and Ca5(AsO4)3-OH were 0.01 and 0.5 mg/L, respectively. Because arsenate apatite is stable to near-neutral pH values, the exten t of its solid solubility with Ca5(PO4)3OH was determined. This was done to assess the effects of phosphate ion on the possible release of arsenate ion. Although equilibrium arsenate ion concentrations increased with decreasing pH, solid solution formation did not occur under ambient conditions. Rather, the arsenate apatite formed at the expense of Ca5(PO4)3OH. 

Biochemical Studies-General; Toxicology-Environmental and Industrial Toxicology; Public Health: Environmental Health-Air