Chemical Engineering Journal ELSEVIER Chemical Engineering Journal 70 ( 1998) 11.5-124 Sorption of dye from aqueous solution by peat Y.S. Ho, G. McKay * Received 27 May 1996; received in revised fotm 22 February 1997; accepted 2 January I998 Abstract The sorption of two dyes, namely, Basic BIue 69 and Acid Bhre 25 onto peat has been studied in terms of pseudo-second order and first order mechanisms for chemical sorption asvrell asanintraparticle diffusion mechani!jm process. The batch sorption process, based on the assumption of a pseudo-second ordermechanism, has been developed to predict the rite constant of sorption. the equ~lib~um capacity and initial sorption rate with the effect of agitation, initial dye concentration andtemperature. An activationenergyof sorption has also been evaluated with the pseudo-second order rate constants. A comparison of the equilibrium sorption capacity evaluated has been made from pseudo-second order model andLangmuir isotherm. 0 1998 Elsevier Science S.A. All rights reserved. Ke~~ol-ds: Peat; Dye; Kinetics; Sorption 1. Introduction For over 20 years, peat has been recognized as a potential agent for the treatment of wastewaters. Several studies have been reported in the literature including its use in cleaningoil spilis [ I], the removal of heavy metals from wastewaters [ 2- 51, the removal of the herbicide [ 61, the treatment of slaugh- terhouse wastewaters, septic tank effluents and dairy wastes [ 7,8]. Pilot plant studies have also been carried out. A peat moss pilot plant filter was used to remove nickel [9]. A moving mat filter was developed on a pilot plant scale to treat textile wastewater [ IO] . In addition, the search for new com- mercial uses of peat has been rewarding in the area of pol- lution control. For the reason of cheaper pollution control methods, Harrison Western Environmental Services of Lak- ewood, CO, has developed such a process, called membrane- media extraction, which uses peat moss ‘capsules’ to be effective at reducing concentrations of arsenic, cadmium, lead, nickel, selenium, and other metals from electroplating rinsewater, pulp and paper mill discharge, municipal waste- water, and acid mine drainage [ 111. Peat is a complex material containing lignin, cellulose, fulvic and humic acids as its major constituents. These com- pounds carry polar functional groups such as alcohols, alde- hydes, carboxylic acids, ketones and phenolic hydroxides, which will become involved in bonding with sorbedpollut~t * Corresponding author. 13858947/98/$19.00 8 1998 Elsevier Science S.A. All rights reserved. PIIS1385-8947(98)00076-X species. The composition of peat from various sources may vary considerably depending on age, the nature of its original vegetation, Ithe regional climate, the acidity of the water and the degree of metamorphosis. The variation of metal ion uptake using 12 types of peat has been demonstrated [ 121. The ability of peat to remove several dyes from aqueous effluent was reported some time ago [ 131. Further studies on single componentadsorptionof basic and acid dye were car- ried out to study equilibrium isotherms [ 141 and diffusion based mass transport processes [ 151. Single and multicom- ponent adsorption isotherms were carried out for three basic dyes [ 16,17]. Detailed analysis of the mass transpo~/~netic mechanisms involved in the sorption process take extensive mathematiciil and computational development [ 1 X] . The aim of the present paper is to test three simple models for analys- ing the sorption of a basic dye, Basic Blue 69, and an acid dye, Acid Blue 25, onto peat and assess their usefulness and accuracy. The three models tested are based on: l a pseudo,-first order process; l a pseudo-second order process; l an intraparticle diffusion process. This work applies the batch sorption results of two dyes, namely, Basic Blue 69 and Acid Blue 25 onto peat, to inves- tigate the influence of intraparticle diffusion and two chemi- cal sorption mechanisms. It compares three rate parameters, fii, for intraparticle diffusion, k2 for the pseudo-second order mechanism and k, for the pseudo-first order mechanism,