Application of Gure modified clay for adsorption of heavy metals in polluted underground water

Kenneth Dagde, Patience Ikenyiri and Peace Yorpah

Abstract

The performance of modified clay obtained from Gure community in Khana Local area of Rivers State as adsorbent for the removal of heavy metals from well water was investigated. This was motivated by the increasing pollution of local wells, the source of water for domestic use by rural dwellers. Effects of dosage, pH, temperature, contact time and initial metal concentration on the capacity of the modified Gure clay to adsorb chromium (VI) (Cr⁶⁺), copper (II) (Cu²⁺) and zinc (II) (Zn²⁺) ions from borehole water were also studied. Adsorption isotherms, kinetics and thermodynamics models were used to evaluate the experimental results. Thus, from 0.5 to 2g dosage, amount of metals removed increased from 69.81 to 83.43% for Cr⁶⁺, 54.51 to 78.24% for Cu²⁺ and 82.15 to 91.16% for Zn²⁺. From 5.5 to 8.5 pH, the amount removed increased from 71.68 to 84.18% for Cr⁶⁺, 64.79 to 80.48% for Cu²⁺ and 78.56 to 92.09% for Zn²⁺. From 30 to 120 min contact time, the amount removed increased from 71.68 to 84.18% for Cr⁶⁺, 64.79 to 80.48% for Cu²⁺ and 78.56 to 92.09% for Zn²⁺. On the contrary, from 29 to 60ºC, the amount removed decreased from 71.68 to 84.18% for Cr⁶⁺, 64.79 to 80.48% for Cu²⁺ and 78.56 to 92.09% for Zn²⁺. Also, from 25 to 100mg/l initial metal concentration, the amount removed decreased from 71.68 to 84.18% for Cr⁶⁺, 64.79 to 80.48% for Cu²⁺ and 78.56 to 92.09% for Zn²⁺. The adsorption of Cr⁶⁺ and Cu²⁺ reached equilibrium at 60 min, while that of Zn²⁺ was at 90 min. All the adsorption isotherms showed good fit, but the Langmuir isotherm correlated better with the experiment. The maximum adsorption capacities obtained from the Langmuir isotherm were 26.738mg/g, 28.902mg/g and 22.831mg/g for Cr⁶⁺, Cu²⁺ and Zn²⁺, respectively. Also, the pseudo second order kinetics compared well with experimental data, while thermodynamic evaluation showed that the adsorption was exothermic, spontaneous and possible within the temperature range. Based on the range of metals removed, Gure modified clay has shown to be good adsorbent for heavy metal removal in contaminated borehole water.