Studies On The Adsorption Of Peat For Lead And Cadmium

Natural pore material-peat is a kind of complex which made up of organiccompounds and inorganics. The material shows better adsorption because of its giant relative surface and lots of activity functional groups,such as carboxyl, phenolichydroxyl group, keto, alcohols'hydroxyl. The adsorption capability of peat for Pb²⁺and Cd²⁺ , competitive adsorption capability of peat for Pb²⁺ and Cd²⁺ mixture in tap water,the competitive adsorption capability of natural peat for Pb²⁺ and Cd²⁺ mixture in water are studied in the experiment. The influence of the dosage of sorbent, initial pH, initial concentration of Pb²⁺ and Cd²⁺, and adsorption time on the adsorption effects were discussed. Furthermore, sorption kinetics,sorption isotherms and chermodynamic on peat were analyzed.Peat has strong adsorbing capacity to Pb²⁺ and Cd²⁺. There are several factors influencing the adsorption of Pb²⁺ and Cd²⁺ by peat including dosage of sorbent, initial pH, initial concentration of the Pb²⁺ and Cd²⁺, temperature and adsorption time. While the volume of solution was 100ml,the dosage of peat between 0.15g and 0.32g, the initial pH between 3 and 6, the temperature between 288K and 318K,the initial concentration of Pb²⁺ and Cd²⁺ between 140mg·L^-1 and 220mg·L^-1 ,the adsorption time between 5min and 90min, the results indicate that the removal rate of Pb²⁺ and Cd²⁺ by peat was increased with the rising of dosage of peat, but the removal rate of Pb²⁺ and Cd²⁺ by peat was reduced with initial concentration of the Pb²⁺ and Cd²⁺; further more the adsorption capacity of the peat was increased with initial concentration of the Pb²⁺ and Cd²⁺,but the adsorption capacity of the peat was reduced with the rising of dosage of peat.The adsorption speed of Pb²⁺ and Cd²⁺ by peat was rapid. The adsorption speed of Pb²⁺ and Cd²⁺ by peat was rised rapidly in 5 minutes. The adsorption equilibrium time is nearly with in 90 minutes.The adsorption dynamics of Pb²⁺ and Cd²⁺ by peat all followed the second-order eqution of Lagergren. The adsorption isotherm of Pb²⁺ by peat fit to both Langmuir equation and Freundlich equation. The adsorption isotherm of Cd²⁺ by peat fit to Freundlich equation. The thermodynamic of Pb²⁺ and Cd²⁺ on peat was analysed. It was found thatâ–³H⁰ >0 indicated the endothermic reaction and high temperature be advantage to adsorption, the adsorption mechanism of Pb²⁺ and Cd²⁺ is mainly characterized by physical adsorption, andâ–³G⁰<0 indicated the adsorption process be the spontaneous, andâ–³S⁰>0 indicated the adsorption reaction be the process of the increasing entropy.The competitive adsorption capability of peat for Pb²⁺ and Cd²⁺ in two different quality of water by natural peat shows that, the removal of Pb²⁺ adsorption by peat was greater than the removal of Cd²⁺.