Simultaneous removal of chromium and arsenate from contaminated groundwater by ferrous sulfate: batch uptake behavior.

Chromium and/or arsenate removal by Fe(II) as a function of pH, Fe(II) dosage and initial Cr(VI)/As(V) ratio were examined in batch tests. The presence of arsenate reduced the removal efficiency of chromium by Fe(II), while the presence of chromate significantly increased the removal efficiency of arsenate by Fe(II) at pH 6-8. In the absence of arsenate, chromium removal by Fe(II) increased to a maximum with increasing pH from 4 to 7 and then decreased with a further increase in pH. The increment in Fe(II) dosage resulted in an improvement in chromium removal and the improvement was more remarkable under alkaline conditions than that under acidic conditions. Chromium removal by Fe(II) was reduced to a larger extent under neutral and alkaline conditions than that under acidic conditions due to the presence of 10 micromol/L arsenate. The presence of 20 micromol/L arsenate slightly improved chromium removal by Fe(II) at pH 3.9-5.8, but had detrimental effects at pH 6.7-9.8. Arsenate removal was improved significantly at pH 4-9 due to the presence of 10 micromol/L chromate at Fe(II) dosages of 20-60 micromol/L. Elevating the chromate concentration from 10 to 20 micromol/L resulted in a further improvement in arsenate removal at pH 4.0-4.6 when Fe(II) was dosed at 30-60 micromol/L.