RECYCLING OF WASTE FE(III)/CR(III) HYDROXIDE FOR THE REMOVAL OF NICKEL FROM WASTE-WATER - ADSORPTION AND EQUILIBRIUM STUDIES

Effects of Ni(II) concentration, agitation time, temperature and pH on adsorption of Ni(II) on Fe(III)/Cr(III) Cr(III) hydroxide, a waste by-product from fertilizer industry, have been investigated. The percent adsorption increased from 55 to 69% with increase in temperature from 20 to 40 degrees C and from 32 to 77% with increase in pH from 3.7 to 7.5 and from 38 to 79% with decrease-in Ni(II) concentration from 100 to 25 mg/L. The equilibrium data fit well with the Langmuir isotherm and the adsorption capacity was found to be 21.0 mg/g at 30 degrees C. Thermodynamic parameters such as free energy change (Delta G degrees), enthalpy change (Delta H degrees) and entropy change (Delta S degrees) were evaluated. The adsorption rate constant was higher at lower concentration of Ni(II) and at higher temperature. Desorption studies show that 70% of Ni(II) can be desorbed from the adsorbent at pH 4.0. The adsorbent was tested using-nickel plating industry wastewater and the maximum percent removal was 97.