Kinetics and thermodynamics of removal of nickel ions from wastewater by use of natural and modified zeolite

Natural and modified (by means of heating, and/or treating with NaOH, NaCl, HCl, CH3COONa) zeolite has been tested in a batch process for its ability to remove Ni2+ from wastewater. The role of some of process parameters on r emoval effectiveness has been investigated for unmodified zeolite. Wastewat er to zeolite ratio of 100:1 has been found as the optimum. Use of zeolite with finer particles increases its uptake ability. Best results have been o btained at pH=5-6 of water to be treated. Presence of Ca2+ and Me in the wa stewater (in relatively high concentrations) decreases the uptake of Ni2+. The uptake process obeys the kinetic equation for the first order irreversi ble reactions. Initially the process of Ni2+ uptake is relatively fast - ov erall rate constants k=3.81x10(-3) and k=4.16x10(-3) min(-1) have been dete rmined for the first 30 min for solutions containing 10 and 50 mg/dm(3) of Ni2+, respectively. Concentrations of 1-2 mg/dm(3) can be reached for less than half an hour, at an initial Ni2+ concentration of 10-15 mg/dm(3). The uptake equilibrium is best described by the Langmuir adsorption isotherm. T he apparent equilibrium constant found, as well as the values of Langmuir c onstants show moderate to low affinity of natural zeolite to Ni2+. Zeolite modification with CH3COONa and NaCl increases (by 25-30 %) its ability to r emove Ni2+ from wastewater and decreases mobilization of Ni2+ caused by con tact of loaded zeolite with acidified water (pH=2.5). Contacting with 2 mol /dm(3) of NaCl solution can easily regenerate loaded natural and modified z eolite. Investigations made have shown that natural and modified zeolites c an be used for treating wastewater released by mines, metallurgical enterpr ises processing Ni-bearing material or resulting from Ni-plating process, a s well as for additional conditioning of liquid wastes from Ni-Cd batteries recycling.