Adsorption Of Lead, Zinc, And Cadmium Ions From Aqueous Solution By Teawaste Adsorbents

In China, the annual production of tea is over3,000,000tonnes and the amount of tea waste produced after processing is over160,000ton/year. Those tea waste can be used as a low cost adsorbent for the removal of toxic heavy metals from the aqueous phase. Batch experiments were carried out to investigate the adsorption of lead, zinc, and cadmium ions from aqueous solution by teawaste adsorbents.This thesis researched adsorption efficiencies of original teawaste towards Pb (Ⅱ), Zn (Ⅱ) and Cd (Ⅱ), and that of treated teawaste to Pb (Ⅱ). The results shows that:1) the adsorption capacity of original teawaste is larger than treated teawaste under same test conditions;2) The gradient of adsorption capacity of original teawaste for three heavy metal ions was as follows:Pb2+>Cd2+>Zn2+;3) pH influenced the adsorption processes very much and removal efficiency goes up along with the increase of pH. The maximum adsorption capacity was found at pH6for the adsorption of lead by both original teawaste and treated teawaste. The maximum adsorption capacity was found at pH7for the adsorption of zinc and cadmium by original teawaste.4) When the initial lead concentration was less than30mg/L given the dosage of original teawaste>10g/L, the residual lead was below0.1mg/L; When the initial zinc concentration was less than30mg/L given the dosage of original teawaste was20g/L, the residual zinc was below2mg/L; When the initial cadmium concentration was less than10mg/L having original teawaste less than20g/L, the residual cadmium was below0.1mg/L, which met the mational wastewater discharge standards respectively;5) The adsorption process overall was fast, according to the fact that95%of the adsorption capacity was reached after reacting for10min and the adsorption equilibrium was reached after reacting for20min.6) Na+, K+had little influences on adsorption, while Ca2+, Mg2+.and the interaction among three metals affects the adsorption quite significantly;7) Original teawaste had good regeneration capacity. There was only a slight decrease of metal adsorbed (5.7%), desorbed (5.5%) and a small loss of mass of adsorbent (13%) after regeneration for4times by0.1M HNO3as eluted solution.The adsorption of Pb(II) by original teawaste and treated teawaste, the adsorption of Zn(II) and Cd(II) by original teawaste all went with pseudo second order model as well as the F-reundlich isotherm, of which R2>0.99. Thermodynamics studies revealed that the four models were all spontaneous and endothermic processes. Adsorption process was dominated by chemical adsorption.The decrease of pH revealed that ion exchange mechanism partially occured in the adsorption process. Compared the FTIR spectra between original teawaste and biosorption of Pb(II) onto,phenolic hydroxyl and carboxyl groups were predominant contributors in biosoption.