Preparation of biochar modified by calcium and humic acid for cadmium pollution remediation
Biochar is a commonly used material for remediation of cadmium contaminated soil,but its efficiency is not high.To improve the adsorption capacity of biochar for Cd2+,rice straw biochar was modified by loading Ca2+and activating modification by humic acid oxidation impregnation.The materials were characterized by scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared spectros-copy(FTIR)and X-ray photoelectron spectroscopy(XPS).Batch adsorption experiments and pot experiments were carried out to explore the adsorption fixation properties and mechanism of the materials for Cd2+.The results showed that:(1)The best adsorption performance was observed when the mass ratio of biochar to humic acid was 1∶1 and the concentration of Ca2+was 1.5 g·L-1(referred to as RHB1-1),and the maximum adsorption capacity was 74.46 mg·g-1,which was 61％higher than that of original biochar.(2)The content of acidic oxygen-containing func-tional groups on the surface of calcium-humic acid modified biochar was significantly increased,and the free hydroxyl group was newly formed.Cd2+was efficiently adsorbed by coordination chelation and complexation co-ion exchange.The adsorption of Cd2+by calcium-humic acid modified biochar was mainly chemisorption,which was consistent with Freundlich adsorption isotherm model.(3)The materials can absorb Cd2+in soil and promote the transformation of Cd2+from an acid extractable state to a residual state,reducing the bioavailability of Cd2+in soil.
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