Study on cadmium adsorption properties of attapulgite/biochar composite material based on orthogonal experiment

The attapulgite/biochar (ATP/C in abbreviation) composites were prepared by carbonization activation method with attapulgite and alkali lignin as raw materials. The orthogonal test was also designed to optimize the preparation process, finding the optimal preparation conditions where the reaction temperature was 600 ℃ and the reaction time 60 min. The mass ratio of ATP and K₂CO₃ was 1∶2 and that of ATP and LG 1∶2. The morphology and structure of the materials were characterized by XRD and SEM. The effects of the dosage, initial concentration, solution pH and temperature on the adsorption of cadmium by ATP/C were investigated in detail, and the adsorption behavior of ATP/C material for cadmium was studied by adsorption kinetics and thermodynamics. The results showed that the adsorption capacity of ATP/C composite for cadmium could reach 82.83 mg/g, when the optimum adsorption condition was pH 4, dosage 80 mg, solution temperature 25 ℃, initial Cd²⁺ concentration 100 mg/L. The adsorption mechanism research showed that adsorption process was spontaneous and conformed to langmuir isotherm model and pseudo-second-order kinetic model. The adsorption process was controlled by monolayer adsorption and chemisorption.