Highlights:  Date seed biochars adsorption capacity Cu 2+ and Ni 2+ were investigated  Biochar with particle size 0.6-1.4 mm and prepared at 550 o C and 3 h was best  Ion exchange mechanism accounted for 70% of the ion removal  Cu 2+ and Ni 2+ adsorption was spontaneous an endothermic process

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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 Pb 2+ ion removal. Therefore, it was selected for further investigation in batch and column experiments. The effects of contact time, initial Pb 2+ 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 (R 2 = 0.97). The adsorption kinetics were best described by pseudo-second-order model (R 2 = 0.94). The breakthrough curve obtained from the column experiment was best described by the modified dose-response model (R 2 = 0.95). The desorption efficiencies of Pb 2+ were 2.1%, 23%, 12%, and 55% for DI water, 0.1 M HCl, 0.1 M CaCl 2 , and a combination of 0.1 M HCl + 0.1 M CaCl 2 eluents, respectively. FTIR analysis and batch experiments results suggested that Pb 2+ 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 Pb 2+ compared to other plant-based biochars reported in other literature.

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