Removal of nickel from groundwater by iron and manganese oxides

Over the last decade, increasing nickel concentrations presumably due to pyrite oxidation have been detected in aquifers in some areas of northwestern Germany. Maximum values of 114 mu g L-1 exceeded the amended German drinking water guideline by nearly sevenfold. Hence, MnCl2H2O is added during water treatment; however, a complete removal of nickel failed. The objective of this study was to evaluate the removal of nickel from groundwater by iron and manganese oxides from waterworks. Therefore, oxides were taken from the pre-filter and secondary filter and investigated in terms of their chemical and physical characteristics as well as their nickel adsorption behavior. Additionally, three further adsorbents (goethite, ferrihydrite and birnessite) were evaluated concerning their applicability for nickel removal. Adsorption experiments were carried out in a batch system as a function of time (1min to 28 days) and pH (2 to 7.5). Furthermore, nickel adsorption was investigated as a function of the equilibrium concentration (0.00315-50mmol L-1), and the data were evaluated with the Freundlich and Langmuir equations. The adsorption of nickel was strongly dependent on time, where a time span of 10min changed the nickel adsorption by +/- 2-8%. Nickel adsorption showed high sensitivity to pH and reached a maximum at pH 7.5. The results indicated that manganese oxides have a higher affinity for nickel adsorption and that adsorption by iron oxides is negligible. Small increases in contact time and an increase in pH during water treatment can promote nickel adsorption. [GRAPHICS] .