Study On Adsorption Capacities Of Cd²⁺ And Pb²⁺ Onto Sediments Collected In The Shallow Area Of Xiangjiang River

Heavy metal pollutants which were discharged into the rivers can be absorbed by surface sediment, The natural adsorption behavior in the water environment has somewhat purification effect on the overlying water. In view of the condition of the heavy metal pollution in Xiangjiang River, this study focused on Xiangjiang River sediment, and studied Xiangjiang River sediment adsorption capacities of Cd²⁺and Pb²⁺, competitive adsorption rule of Pb²⁺and Cd²⁺, anti desorption capacities after adsorption of Pb²⁺ and Cd²⁺.Firstly, we investigated the influence of different reaction conditions on the adsorption capacities in single heavy metal ions adsorption system. The results showed that the value of p H has significant effect on the adsorption of Cd²⁺ and Pb²⁺, the removal rate of Cd²⁺, Pb²⁺ increase with the an increase of p H value, It was found that the removal rate of Cd²⁺ and Pb²⁺ remained stable and close to the maximum value When the initial solution p H range from 5 to 7.5 of Cd²⁺ and range from 4.2 to 6.6 of Pb²⁺; When the initial solution p H was 6.5, the initial concentration of Cd²⁺ and Pb²⁺ was 30mg/l and 45.25mg/l and the sediment dosing quantity reached 10g/l and 7.5g/l, the residual concentration of Pb²⁺ and Cd²⁺ were 0.07 mg/l and 0.9 mg/l, which all meeted the state wastewater discharge standards; The adsorption of Pb²⁺ and Cd²⁺ showed a rapid period among early 30 minutes, and reached 92% adsorption capacities of Cd²⁺ and 95% adsorption capacitiesof Pb²⁺,the adsorptionequilibrium was reached after 2h; The adsorption capacities of Cd²⁺, Pb²⁺ decreased with the increase of ionic concentration, when the ionic concentration was 0.2 mol/l, Cd²⁺ and Pb²⁺ adsorption capacities reduced as much as 20.4% and 19.05%, respectively.Kinetic experiments showed that the pseudo-second-order dynamic model can well give a explanation of adsorption process of Cd²⁺ and Pb²⁺ onto the sediments, adsorption of Cd²⁺ and Pb²⁺ was chemisorption-based. Thermodynamics experiments showed that the sediment adsorption of Cd²⁺, Pb²⁺ at three temperatures were highly fitted by the Langmuir isotherm model, which showed that this kind of adsorption is monolayer adsorption. The maximum adsorption capacities of Cd²⁺, Pb²⁺ reached 9.75 mg/g and 23.75 mg/g, which indicated that the Xiangjiang River sediment has a great potential on adsorption of Cd²⁺and Pb²⁺. Enthalpy change??H? of Cd²⁺, Pb²⁺ in the process of adsorption were 2.996 k J/mol and 3.16 k J/mol, respectively, and all were greater than zero, which explained that the adsorption of Cd²⁺, Pb²⁺ onto the sediment is an endothermic reaction.Compared with adsorption of single heavy metal ions, adsorption capacities of Cd²⁺, Pb²⁺ has shrunk under competitive adsorption, the adsorption capacit ies of Cd²⁺ decreased about 40% on average, Pb²⁺ reduced 17% on average, which showed that the adsorption capacities of Pb²⁺ onto sediments of Xiangjiang River is stronger than the adsorption capacities of Cd²⁺, adsorption choice of Pb²⁺ onto sediments also takes precedence over adsorption of Cd²⁺.Aerated was carried out in the adsorption equilibrium solution, it leads to the adsorption equilibrium concentration of Cd²⁺, Pb²⁺increased and brings desorption phenomenon, but desorption quantity very low and resolution effect is not obvious. Adsorption saturation sediment in adsorption equilibrium solution washed by Double-distilled water did not produce significant desorption effect, and with the increasing of washing time, desorption rate of Cd²⁺ and Pb²⁺ gradually decreased, Both illustrated that the Xiangjiang River sediment adsorption of Cd²⁺, Pb²⁺ has a strong stability, and desorption phenomenon was not easily generated.