Removal of Ni2+ and Zn2+ from groundwater by adsorption onto fishbone and hydroxyapatite: Effect of salinity

초록

Ni2+- and Zn2+-contaminated groundwater in the coastal regions is a serious threat to water security in industrial areas. Apatite-like material is an excellent sorbent for heavy metals; however the effect of salinity on the Ni2+ and Zn2+ adsorption onto fishbone and synthesized hydroxyapatite (HAP) has not been investigated. This study investigates the effect of salinity on the single and binary adsorption of Ni2+ and Zn2+ onto apatite-like materials. The experiments were conducted in batch reactor for 24 h at 1:40 solid-to-liquid ratios (wt/wt), 25 degrees C, and pH 5. Freundlich, Langmuir, and Dubinin-Radushkevich models fit well with the single-adsorption data. The adsorption isotherms were nonlinear (N-F = 0.350-0.710). The maximum adsorption capacities (q(mL)) of the Ni2+ and Zn2+ onto HAP were higher than those onto the fishbone, attributed to the higher Brunauer-Emmett-Teller surface area (A(BET)) and cation exchange capacity. In the binary adsorption, adsorption capacities of the adsorbents were less than those in the single-solute system due to the competition between Ni2+ and Zn2+. Salinity affected the single and binary adsorption by decreasing the adsorption capacities of the adsorbents. In a binary adsorption system, the selectivity of Zn2+ was less than that of Ni2+ for both fishbone and HAP at 0 parts per thousand and 30 parts per thousand salinity, respectively. Binary adsorption models, such as the Murali-Aylmore (M-A) model, competitive Langmuir model (CLM), P-factor model, and ideal-adsorbed solution theory coupled with the Freundlich (IAST-Freundlich) model were used; of these, the M-A model provided the best prediction for the binary system.

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