This study explored the adsorption of lead ion from aqueous solution onto biochars produced from date seed biomass. Initial evaluation of nine date seed-derived biochars showed that biochar prepared at 550 °C and heating time of 3 h (DSB550-3) was the best adsorbent for Pb²⁺ ion removal. Therefore, it was selected for further investigation in batch and column experiments. The effects of contact time, initial Pb²⁺ concentration, and solution pH were studied. Solution pH showed strong effect on the adsorption ability of DSB550-3 biochar to the lead ion, and the maximum adsorption capacity was found to occur around pH 6.0. The batch maximum adsorption capacity of DSB550-3 biochar was 0.360 mmol g⁻¹. The equilibrium data were adequately fitted to Freundlich and Langmuir isotherms (R² = 0.97). The adsorption kinetics were best described by pseudo-second-order model (R² = 0.94). The breakthrough curve obtained from the column experiment was best described by the modified dose–response model (R² = 0.95). The desorption efficiencies of Pb²⁺ were 2.1%, 23%, 12%, and 55% for DI water, 0.1 M HCl, 0.1 M CaCl₂, and a combination of 0.1 M HCl + 0.1 M CaCl₂ eluents, respectively. FTIR analysis and batch experiments results suggested that Pb²⁺ adsorption mechanism was dominated by complexation with active surface groups, precipitation, and cation exchange. Experimental and model results suggested that date seed-derived biochar has high adsorption capacity for Pb²⁺ compared to other plant-based biochars reported in other literature.

In a multicomponent systems, the adsorption of Pb²⁺, Cu²⁺, and Ni²⁺ by date seed biochar exhibited competitive behavior. Compared to single component systems, the adsorption capacities of each ion were reduced by 48–75% in both batch and column experiments. Surface complexation with carboxyl and hydroxyl functional groups played a major role in the removal mechanism. Ion exchange mechanism accounted for 37–40% of the total adsorption compared to 57–72% in single component systems. Modified Langmuir isotherm best described the systems. Adsorption capacities and selectivity follow the order: Pb²⁺> Cu²⁺> Ni²⁺. Multi-stage sequences system is recommended to avoid premature exhaustion of biochar.

The excessive application of phosphorus in agricultural lands leads to serious environmental issues. Efficient application is beneficial from an economic and environmental perspectives. Biochar can be used as a carrier for slow release of phosphate. However, its adsorption capacity is limited. In this work, biochar was prepared at different pyrolysis temperatures (350–550 °C). The biochar prepared at 550 °C had the highest adsorption capacity and was selected for modification by magnesium impregnation. Magnesium modification enhanced the adsorption capacity by 34% to a theoretical max adsorption capacity of 463.5 mg·g⁻¹. The adsorbed phosphate can be desorbed. The desorption was bi-phasic with fast- and slow-release fractions. The distribution of the phosphate fractions was pH dependent with slow release being most prominent in neutral conditions. Mg modified biochar can be used to recover phosphate and then used as a carrier for slow release of phosphate. The bi-phasic desorption behaviour is useful as the fast release fraction can provide the immediate phosphate needed during plant establishment, while the slow-release fraction maintains steady supply over extended periods.