Adsorption Characteristics of Cd²⁺ and Pb²⁺ in Wastewater by 4 Agricultural Wastes

In order to discuss the adsorption characteristics of different agricultural wastes on Cd²⁺ and Pb²⁺ in wastewater, the powder of peanut straw (HG), sunflower faceplate (KP), cotton husk (MK) and cotton straw (MG) were selected for the study. The studied adsorption characteristics include dosage, solution pH, adsorption time, initial solution concentration and ionic strength. The results show that the adsorption capacities of Cd²⁺ and Pb²⁺ by the peanut straw, sunflower faceplate and cotton husk decreased exponentially or logarithmically when the dosage increased from 0.025 g to 0.200 g (P < 0.05). With the increasing pH, the adsorption capacities of Cd²⁺ and Pb²⁺increased initially and then remain unchanged. Those of peanut straw and cotton husk are significantly higher than the other two materials (P < 0.05). The sorption kinetics of Cd²⁺ and Pb²⁺ on the four materials follows the pseudo-second order model. Isothermal adsorption of Cd²⁺ and Pb²⁺ by HG, KP, and MK fitted well with Langmuir equation, while Freundlich equation is more suitable for the MG. The maximum adsorption capacity of the four materials on Cd²⁺ and Pb²⁺ was 59.18-93.13 mg·g^-1 and 106.43-167.73 mg·g^-1, respecrtively. The existence of Na⁺ can significantly reduce the adsorption capacities on Cd²⁺ by the four materials and on Pb²⁺ by cotton straw (P < 0.05).