Study On The Adsorption Of Sepiolite For Lead And Cadmium

Natural pore material-sepiolite,a kind of clay mineral for fibrous silicate, was studied in the paper. The material shows better adsorption because of its giant relative surface and the unique holestructure. The adsorption capability of Pb²⁺ and Cd²⁺ by natural sepiolite and heated sepiolite was studied. The influence of the dosage of sorbent, initial pH, initial concentration of Pb²⁺ and Cd²⁺, and adsorption time on the adsorption effects were discussed, sorption kinetics. Sorption isotherms and chermodynamic on sorbent were analysed.Sepiolite has strong adsorbing capacity to Pb²⁺ and Cd²⁺. Adsorption capability was improved by heated sepiolite with muffle. There are several factors influencing the adsorption of Pb²⁺ and Cd²⁺ by sepiolite including dosage of sorbent, initial pH, initial concentration of the Pb²⁺ and Cd²⁺, temperature and adsorption time. With the rising of dosage of sorbent, initial pH, temperature and adsorption time, the removal rate of Pb²⁺ and Cd²⁺ by sepiolite was increased and with the rising of initial concentration of the Pb²⁺ and Cd²⁺,the removal rate of Pb²⁺ and Cd²⁺ by sepiolite was reduced. The adsorbing effects of the two kinds of sorbent for Pb²⁺ and Cd²⁺ were adsorption capality of Pb²⁺ and Cd²⁺ by heated sepiolite> adsorption capality of Pb²⁺ and Cd²⁺ by natural sepiolite.The adsorption speed of Pb²⁺ and Cd²⁺ with the two kinds of sorbent was rapid.The removal rate and adsorption capacity of Pb²⁺ and Cd²⁺ rised rapidly in 5 minutes. The adsorption equilibrium time is nearly with in 90 minutes. The adsorption dynamics of Pb²⁺ and Cd²⁺ with the two kinds of sorbent all followed the second-order eqution of Lagergren. The adsorption isotherm of Pb²⁺ with the two kinds of sorbent fit to the Langmuir equation, and the adsorption isotherm of Cd²⁺ by sepiolite fit to both Langmuir equation and Freundlich equation. The thermodynamic of Pb²⁺ and Cd²⁺ on sepiolite was analysed. It was found thatâ–³H 0 >0 indicated the endothermic reaction and high temperature be advantage to adsorption, thatâ–³G 0<0 indicated the adsorption process be the spontaneous, thatâ–³S0>0 indicated the adsorption reaction be the process of the increasing entropy. The adsorption mechanism of Pb²⁺ by sepiolite includes both chemical adsorption and physical adsorption, but adsorption mechanism of Cd²⁺ by sepiolite only includes physical adsorption.