Removal of heavy metals from industrial effluent using Pinus roxburghii leaves as biosorbent: equilibrium modelling

In the present study, biosorption capability of pine (Pinus roxburghii) leaves for the removal Cr(6+), Cu(2+), Fe(2+) and Zn(2+) ions, present in brass and electroplating industry effluent, were investigated with respect to different adsorbent doses, contact time and pH. Heavy metals concentrations were estimated by atomic absorption spectrophotometry. Initial concentration of Cr(6+), Cu(2+), Fe(2+) and Zn(2+) ions in the effluent were found to be 2.741, 4.551, 8.820 and 5.529 mg/L respectively. Biosorption studies revealed that Cr(6+), Cu(2+), Fe(2+) and Zn(2+) showed maximum removal of 99.85, 94.54, 97.10 and 89% at pH 4, 4, 4 and 8, respectively, with 4 g pine leaves when shaken at 150 rpm for 60 min. The applicability of the three equilibrium isotherm models was investigated and the data obtained fitted the three investigated isothermal models in the order: Langmuir > Temkin > Freundlich for all the studied metal ions. The adsorption isotherm coefficients, Qmax, b, Kf, n, at, bt were also calculated. Very high regression correlation coefficients (R(2) > 0.9) were found for Cu(2+), Fe(2+) and Zn(2+); Cr(6+) (Temkin isotherm) when pH (2-8) was varied; Cr(6+), Cu(2+),Fe(2+) and Zn(2+) when contact time (15-60 min) was varied; Cu(2+) (Langmuir isotherm) Fe(2+) (Freundlich and Temkin isotherms) when adsorbent was varied from 2 to 5 g. Results also revealed that among all the studied ions Cr(6+) at varied pH and Fe(2+) at different adsorbent doses satisfy the Temkin and Freundlich isotherm models to describe the biosorption equilibrium by pine (Pinus roxburghii) adsorbent.