Effect of dissolved organic matter on the adsorption and stability of As(V) on manganese wad

The efficiency of manganese wad to adsorb As(V) was tested as a function of pH, contact time, adsorbent dosage, and initial As(V) concentration. The effect of dissolved organic matter (DOM) on the adsorption properties of As(V) and stability of As(V) bearing manganese wad was also studied. The major mineral phases found in the manganese wad were goethite, hematite, lithiophorite, and gibbsite. Under optimum conditions (pH 6.5, adsorbent dose 30 g/L), As(V) was lowered to 0.42, 0.18, and 0.05 mg/L from 10, 5, and 2.5 mg/L, respectively, in the solution. Adsorption capacity was calculated from the Langmuir isotherm model and found to be 2.15 mg/g adsorbent. The presence of DOM had significant negative effects on As(V) adsorption in the whole pH range studied, whereas the corresponding data for DOM adsorption in presence of As(V) were pH dependent. Leaching studies showed that DOM could extract maximum 4.16 mg/L (4.40%) of the adsorbed As(V) under optimum conditions from As(V) loaded manganese wad residue.