King Coconut Husk Derived Biochar through Hydrothermal Activation Process for the Removal of Cadmium (II) and Copper (II) from Aqueous Media

This research was conducted to study the removal of the most prevalent heavy metal ions cadmium (II) and copper (II) by adsorption on King coconut (Red Dwarf coconut, cocos nucifera. var) husk biochar. Raw king coconut biochar (RKH) and steam activated King coconut biochar (AKHC) were prepared and analysed for physical properties, surface properties, elemental composition and functional properties to identify the sorbent suitability. The efficiency of adsorption of heavy metal ions [cadmium (II) and copper (II)] on biochar were studied with batch sorption experiments. Adsorption capacities of RKH and AKHC for cadmium (II) and copper (II) at different pH, initial metal concentrations, ionic strengths and contact times between adsorbent and adsorbate were measured. Scanning electron microscopy reveals the existence of a better and highly porous structure in AKHC than that of RKH, that could be a result of the volatilization by steam process. EDX analysis indicates a carbonized structure for both adsorbents. Further, it was observed that the adsorption of Cd and Cu ions by AKHC could be increased with increasing pH and decreased with ionic strength. Supported point of zero charge pH_pzc (5.8, 6.9)can be used to explain the effect of pH on the higher adsorption process at higher pH. The maximum adsorption capacities of Cd and Cu of AKHC were 22.24, 34.24 mg g^−1, respectively, and they were considerably lower for RKH with 17.22, 21.25 mg g^−1. With well-fitting of Freundlich isotherm, it revealed the heterogeneous properties of the surfaces and favourable adsorption process. The kinetics fittings of pseudo second order were accommodated towards chemisorption process for both Cu and Cd. The higher sorption ability expressed by AKHC and RKH, prepared in this study, show their potential sorbent activity for environmental remediation application.