Characterization and utilization of mesoporous fertilizer plant waste carbon for adsorptive removal of dyes from aqueous solution

This paper presents the physico-chemical characteristics of low-cost fertilizer plant waste carbon (WC) for the adsorption of different dyes. The particle size analysis showed an average particle size of 167.35 mu m. Proximate and CHIN analysis showed the presence of high amount of carbon in WC. Bulk density and heating value of WC were found to be 308.03 kg/m(3) and 22.3 MJ/kg, respectively. The pore size distribution results showed that the WC was predominantly mesoporous. The BET surface area was 357 m(2)/g. The average pore diameter by BET was 6.483 nm. The mesoporous surface area for adsorption was 96% of the total pore surface area. The polar groups present on the WC surface imparted considerable cation exchange capacity to it. WC was further used as an adsorbent for the removal of Auramine-O (AR), Congo red (CR), Orange-G (OG) and methyl violet (MV) dyes from aqueous solutions. Optimum initial pH (pH(0)) was found to be 7.0. WC dose of 1 g/l was found to be optimum for the adsorption of all dyes at a concentration of 20 mg/l. The adsorption of dyes on WC was found to be gradual process and quasi-equilibrium reached in 5 h. The adsorption kinetics followed pseudo-second-order kinetics. The effective diffusion coefficient was of the order of 10(-12) m(2)/s. Error analysis showed that Redlich-Peterson (R-P) isotherm best represented the equilibrium adsorption data for all the dyes. Thermodynamics showed that the adsorption of CR on WC was most favourable in comparison to other dyes. The desorption study showed that the recovery of dyes and the regeneration of the WC using different solvents viz. water, acids and alkalies were not feasible. Spent WC can, however, be used as a fuel to recover its high energy content and the bottom ash obtained after its combustion/incineration can be blended with clay/cement-concrete mixture to make bricks and building blocks for its safe disposal. WC has been found to have high potential as an adsorbent for the removal of AR, CR, OG and MV dyes from aqueous solutions. (c) 2006 Elsevier B.V. All rights reserved.