Lead (Pb) and cadmium (Cd) are considered as a typical heavy metals in aqueous solution, which may pose adverse health effects on human beings. For the removal of these two pollutants, magnesium oxide (MgO) was successfully immobilized onto eucalyptus biochar (BC) matrix via simple and cost-effective pyrolysis process of MgCl₂-pretreated eucalyptus biomass under high temperature (500 °C). Synthesized MgO nanoparticles-biochar composites (MBC) exhibited superior removal performance for target pollutants, and achieve 99.9% removal efficiency for Pb(II) and Cd(II) at optimum conditions (0.02 g, pH in range of 4-7, and reaction time 120, 240 min). Furthermore, the maximum theoretical adsorbing amount of MBC was 829.11 mg/g for Pb(II) and 515.17 mg/g for Cd(II). Pseudo-second-order model and Langmuir models were well-determined for isotherm and adsorption kinetics. FTIR, XRD, and XPS analysis revealed that precipitation and ion exchange was of great importance for the removal of contaminants. Besides, cation-π interaction and complexation from the carbon-containing functional groups should not be neglected. Considering the advantage of low-cost, facile preparation, and brilliant adsorption capacity, it is anticipated that MBC has a promising prospect for the broad application in Pb(II)/Cd(II)-containing wastewater treatment.

The preparation process and method of magnetic water hyacinth(MBC) were conducted, and the morphological structure and surface characteristics of biochar were characterized. The optimal MBC preparation method was obtained under different carbonation temperatures, impregnation times, and mass ratio of potassium carbonate to water Gourd: carbonization temperature is 450 °C, iron nitrate concentration is 0.2 M, and the mass ratio of potassium carbonate to water hyacinth is 0.5:5.

Zeolite was modified by ferric chloride(Fe-Z) removal Cr (VI) ion from wastewater. The results showed that the effect of Cr(VI) adsorption on modified zeolite depended significantly on pH. It is favorable for the adsorption of Cr(VI) in acid condition. The Langmuir isotherm model has high fitting accuracy with experimental data, demonstrated that is monolayer adsorption and chemical adsorption.The pseudo-second-order equation provided the best correlation to the data. The model can describe the adsorption reaction process well.

Amino modified eucalyptus biochar (ABC) was prepared from eucalyptus biochar by amino amendment with ammonia, concentrated nitric acid, concentrated sulfuric acid and sodium dithionite. The preparation parameters of ABC were optimized by orthogonal experiment. It was found that the optimal preparation process of ABC was: carbonization temperature was 300°C, volume ratio of nitric acid to sulfuric acid was 2:1 and the consumption of ammonia water was 15 ml. The results of characterization indicated that the morphological structure of ABC changed, and the amino functional group was successfully loaded on the surface of the biochar.