Sorption of Ni(II) on surface of bed grains used in iron and manganese removal filters

This paper reports the results of determinations of crystalline phase type, specific surface area, point of zero charge pH (pH(pzc)), and Ni(II) sorption capacities of beds for groundwater treatment. Bed materials from iron and manganese removal filters (FeRF, MnRF) as well as a catalytic bed (G1) were investigated. The reference material was MnO2-coated quartz sand (MnQS). The efficiency of Ni(II) sorption was investigated as a function of pH. It was found that the naturally formed coating on FeRF was characterised by the highest sorption efficiency (80-88%) in the wide pH range (4-9) of the solution. Sorption on MnRF was weaker (35-45%). G1 and MnQS, which contained only manganese oxides, were characterised by a very low sorption efficiency of 0-6% and 3-8%, respectively. A lower Ni(II) removal efficiency was observed at an initial pH close to the pH(pzc) values. During Ni(II) sorption, the pH of the solution was not constant and tended towards the value of pH(pzc) for all tested materials. The slightly pH-dependent sorption of Ni(II) indicates that its removal depends more on the chemical composition and the specific surface area of the oxide coatings covering the bed materials.