Kinetic study on the removal of heavy metals by Cajanus Cajan husk

Abstract

The removal of heavy metals from wastewater has become crucial to meet safe discharge standards. Development of more economic process has been strived owing to high cost of adsorbents. Thus, biosorption process has become the area of interest to researchers and engineers. The present study has carried out the transient removal of heavy metals from wastewater by both physically treated and chemically modified Cajanus cajan (Pigeon pea) husk (CCH) as novel biosorbents. Work includes five different models such as first order, second order, nth order, first order reversible and second order reversible under the heading of prediction of transient concentration of metal in the solution are used, and under the heading of prediction of transient metal uptake capacity; fractional power, pseudo first order, pseudo second order, second order reversible, Elovich, intra-particle diffusion and film diffusion models are used to analyse the kinetic data. For a metal at any particular initial concentration the best kinetic model with the least RMSE is identified. Pictorial comparison between experimental and pseudo second order and pseudo first order model predictive data of Cd(II) and Cu(II) transient biosorption, respectively onto CCH are illustrated. The trend of the results shows a successful prediction capability of all the kinetic models used in the present work. According to RMSE data, it can be concluded that the best kinetic models are pseudo second order for Cd(II) and pseudo first order for Cu(II). It has been found that the required equilibrium time is always less for the chemically activated than the physically activated sorbent. At 100 mg/L initial metal concentration, pseudo-first-order model has been identified as the best kinetic model for the transient Cu(II) and the best kinetic model for fitting the transient sorption of Cd(II) on CCH is pseudo-second-order. At initial metal concentration of 150 mg/L, initial biosorption rate of 9.7038 for Cd(II) on CCH(N) is greater than 1.4553 for Cu(II) on CCH(N). These indicate that Cd(II) undergoes faster adsorption rate than Cu(II) onto CCH.