Biosequestration of chromium (VI) from aqueous medium using carbonaceous adsorbents derived from Eichhornia crassipes

Abstract

Utilization of the biochar that are derived from Eichhornia crassipes (water hyacinth) as biosorbent for Cr (VI) adsorption was investigated. The biochar was characterized before and after Cr (VI) adsorption by SEM, FTIR and EDX. The influencing parameters viz., solution pH, solute concentrations, reaction duration, adsorbent dose and size have been examined. The most favorable conditions for Cr (VI) removal were found to be pH = 2.0, adsorbent size = 0.2 mm, adsorbent dosage = 2.5g/100ml, adsorbate/solute concentration = 100mg/L of Cr (VI) at 25ºC at 250 rpm. Rate of adsorption was rapid and equilibrium was reached at 36 hours. The equilibrium relationship between the sorbent and sorbate was determined using the isotherms Langmuir, Freundlich and Temkin models. The Langmuir dimensionless constant (KR) for each of the solute concentration was ranged between 0 and 1, it indicates the favourable adsorption of Cr (VI) onto the adsorbent. Adsorption data was very well explained through Langmuir isotherm where sorption occurs on monolayer with the maximum biosorption capacity of 55.55 mg/g. Adsorption rate and its mechanisms were elucidated through kinetic studies viz., Pseudo first order, second order, elovich and intra particle diffusion models. On comparison with various kinetic models, results fitted excellently with pseudo second order model (R2 = 0.999). It suggests that Cr (VI) adsorption by could be better described by chemisorption which involves sharing of electrons between adsorbents and adsorbate. Hence, the biochar derived from E. crassipes are efficiently used as an ecofriendly biosorbent for the management of Cr (VI) rich waste water.