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Removal of Arsenic(III) and Arsenic(V) Ions from Aqueous Solutions with Lanthanum(III) Salt and Comparison with Aluminum(III), Calcium(II), and Iron(III) Salts
Author(s) -
Tokunaga S.
Publication year - 1999
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.2175/106143098x121833
Subject(s) - arsenic , lanthanum , chemistry , aqueous solution , inorganic chemistry , precipitation , arsenate , solubility , chloride , salt (chemistry) , nuclear chemistry , physics , organic chemistry , meteorology
Interactions of arsenic(III) and arsenic(V) ions with a lanthanum salt were studied with the aim of developing a new precipitation method for removal of arsenic from aqueous solutions. Performance was compared to those of aluminum, polyaluminum chloride (PAC), calcium, and iron(III) salts. Arsenic(III) was removed by iron(III) and lanthanum in a narrow pH range with less than 60% removal. Arsenic(V) was removed more efficiently by aluminum, PAC, iron(III), and lanthanum. Lanthanum was most effective, meeting Japanese effluent and drinking water standards by adding three times as much lanthanum as arsenic(V). The stoichiometry and X‐ray diffraction measurement showed that the precipitation reactions are
La 3+ + H 2 AsO 4 − → LaAsO 4 + 2H + (pH 5) (1)
and
La 3+ + HAsO 4 2− → LaAsO 4 + H + (pH 9) (2)
The solubility product of lanthanum arsenate, LaAsO 4 , was calculated to be 1.07 ± 0.03 × 10 −21 .