Removal of Zinc, Nickel and Copper Ions from Waste Water Using Char-A Sponge Iron Plant Waste

Abstract

Adsorption is a well known technology to address water solution problem typically for heavy metal pollution. Batch studies for individual heavy metals such as Zinc, Copper and Nickel was investigated using adsorbent, sponge iron plant waste. Surface modification of the adsorbent was achieved using HCl treatment. Surface characterization using proximate and ultimate analysis indicated improved in carbon content. FTIR, BET, SEM/ EDX, analysis further confirmed its surface modification. Batch studies were conducted to explore the influence of various parameters such as initial solution pH, adsorbent dosage, contact time, temperature etc. The optimum conditions obtained were 28min contact time, pH 7, adsorbent dosage 1g/L, and 25°C temperature for Zinc, 30min contact time, pH 6.5, adsorbent dosage 1g/L, 25°C temperature for nickel and 30 min contact time, pH 6, and temperature 25°C for copper.
Adsorption data obtained was fitted to various model equations such as Freundlich, Langmuir, Temkin etc; that suggest best fit to Langmuir isotherm model. The maximum adsorption capacity of zinc, nickel and copper from Langmuir isotherm were found to be 64.10mg/g, 14.08 mg/g and 11.79 mg/g respectively. The RL values for initial concentration range 10mg/L-100mg/L were 0.92-0.54, 0.2 – 0.02 and 0.52-0.09 for Zn, Ni and Cu respectively that were within the favorable range (0<RL<1). The necessary data obtained were interpreted kinetically by using pseudo first order, and pseudo second order rate kinetics. In all the cases the kinetics followed pseudo second order rate equation. The contact time variation experiments were used to study the rate-determining step in the adsorption process. Among the two diffusion models film diffusion was considered to be the rate controlling step in the adsorption mechanism because of its lower diffusion coefficients. The negative values of ΔG◦and ΔH◦ indicate that the process was thermodynamically spontaneous and exothermic in nature.
In Co adsorption studies using batch experiments there was no significant effect on the adsorption of zinc due to the presence of nickel. In contrast, the removal of nickel decreased from 57.40% for the single-ion nickel solution to 48% in the presence of zinc co-adsorption.
The ability of SIP waste to adsorb zinc and nickel in a fixed bed column was investigated using Perspex fixed bed column. The effects of operating parameters such as bed height and flow rate were studied. The percentage metal adsorption increased from 40% – 62.05% and 31.23%- 56.43% for zinc and nickel respectively with increase in bed height form 5cm to 15cm. Increase in flow rate from 10mLmin-1 to 20mLmin−1 witnessed decrease in removal from 60.75% to 40.92% for zinc and 56.17% to 31.23% for nickel. At the end, an attempt has also been made to model the data generated from column studies using the empirical relationship based on Thomas model. From the results it was observed that Qo values calculated from the Thomas model is close to the Q, exp values obtained experimentally for both zinc and nickel. The column regeneration studies were carried out for one adsorption–desorption cycle using the elutant 0.1N HCl. On the basis of the results, SIP waste can be economically and efficiently used as an adsorbent for the removal of metal ions from wastewaters