The removal of As(V) from wastewater containing low concentration of As(V) was investigated by addition of Fe(III), Al or Pb salts. Results show wastewater that contains 5 mg/dm³ As(V) is reduced below the regulated concentration of Japanese effluent standard (0.1 mg/dm³) when treated at pH 4.5∼7.5 with the addition of 50 mg/dm³ Fe(III) salts and at pH 6∼8 with the addition of 20 mg/dm³ Al salts. Successful removal of 3.75 mg/dm³ As(V) in wastewater is also possible when treated at pH 7∼11 with the addition of 20.7 mg/dm³ Pb salts, subsequently reducing Pb concentration below the regulated concentration of Japanese effluent standard (0.1 mg/dm³).
Chemical equilibrium calculation which considering the formation of arsenic salts with Fe(III), Al or Pb hardly explains the experimental results. Furthermore, as the concentration of As(V) increases, the isoelectric point (IEP) of precipitations after the removal of As(V) by Fe(III), Al or Pb shifted to acidic pH. It is surmised that As(V) is removed by adsorption on the surface of ferric, aluminum or lead hydroxide.
Solid/liquid separation from these As(V) removal experiments using a column bed method packed with fibrous ferro-nickel slag was also investigated. Ferric, aluminum or lead hydroxide particles adsorbing dilute As(V) that have several hundred nm in sizes, are thinly dispersed and can perform rapid solid/liquid separation (2.5mm/sec).