Study on adsorption/desorption of as by mine sludge depending on pH and natural organic matter

Abstract

Acid mine drainage (AMD) sludge, which is a waste product from AMD treatment, and synthesized ferrihydrite were used as an adsorbent substance to remove dissolved As(III) and As(V). To investigate the influence of pH value and organic matter on arsenic retention, a comparative study of adsorption and desorption behavior of arsenic was conducted. AMD sludge and ferrihydrite removed more than 80% of As(III) and As(V) within 10 min in acid to neutral condition. The maximum adsorption capacity of mine sludge (125 mg/g) was greater than that of ferrihydrite (98.04 mg/g) in arsenite. As(V) species dominated in oxidizing environment could be easily affected by pH more than As(III). In the kinetic adsorption with organic matter, the possibility of desorption of arsenic was not detected. Although the concentration of organic matter was increased to high figure in natural water, almost of As(III) and As(V) was removed within 10 min. In contrast to previous study, competitive adsorption of organic matter slightly enhanced adsorption of As(V) from the result of kinetics adsorption. Because of forming complexion between arsenic and natural organic matter, adsorption on ironcontaining adsorbents was enhanced and reached to the equilibrium state. In desorption, As(V) was highly desorbed only in intensive alkaline condition. Outcomes from these studies could suggest that it was very profitable to use waste mine sludge as an effective adsorbent by comparing adsorption capacity of ferrihydrite. These findings also raised the possibility of desorption followed by re-dissolution of reduced arsenic by natural attenuation in AMD. © 2013 Taylor & Francis.