Sorption of Hg(II) onto Carica papaya: Experimental studies and design of batch sorber

A novel sorbent, Carica papaya, was evaluated for sorption of Hg(II) from aqueous solution under the varying conditions of contact time, metal ion concentration, sorbent dose and pH. The results indicate that sorption equilibrium was established in about 120 min. The Hg(II) sorption was strictly pH dependent, and maximum removal was observed at pH 6.5. The sorption interaction of Hg(II) onto C. papaya obeyed the pseudo-second order rate equation. The batch biosorption rate for the system based on an intraparticle diffusion rate parameter derived from the plots of Hg(II) sorbed versus the square root of time indicated that the adsorption mechanism was predominantly intraparticle diffusion but there was also a dependence on pore size as the Hg(II) diffuses through macro-, meson-, and microspores. The sorption isotherm data provided a very good fit to the Langmuir isotherm equation with a monolayer sorption capacity of 155.6 mg g−1 and the regression coefficient (R2) 0.9959 with low S.E. and SSE values. A design procedure was proposed using the Langmuir isotherm to design a two stage sorption system to minimize the amount of biomass required for the treatment of Hg(II) solution using C. papaya. Desorption studies indicated that the maximum percent recovery of Hg(II) was 96.7 ± 0.80 with 0.1 N HCl and 99.0 ± 0.49 with 1% KI.