Biochar can be used as a sorbent to remove inorganic pollutants from water but the efficiency of sorption can be improved by activation or modification. This review evaluates various methods to increase the sorption efficiency of biochar including activation with steam, acids and bases and the production of biochar-based composites with metal oxides, carbonaceous materials, clays, organic compounds, and biofilms. We describe the approaches, and explain how each modification alters the sorption capacity. Physical and chemical activation enhances the surface area or functionality of biochar, whereas modification to produce biochar-based composites uses the biochar as a scaffold to embed new materials to create surfaces with novel surface properties upon which inorganic pollutants can sorb. Many of these approaches enhance the retention of a wide range of inorganic pollutants in waters, but here we provide a comparative assessment for Cd, Cu, Hg, Pb, Zn, NH, NO, PO, CrO and AsO.
Apparent molar volumes (V L ) and viscosities of lauric, palmitic, and stearic acids as a function of concentration at (20, 30, 40, and 60) °C in 2-butanol are reported. The apparent molar volumes at infinite dilution (V°L) were determined by extrapolating V L values to zero concentration. The variations of both V°L and viscosity values with temperature and with chain length of fatty acid were examined. V°L values were found to decrease with increasing temperature for all three fatty acids and to increase with increasing chain length of fatty acid at a constant temperature. Apparent molar expansivity data at infinite dilution (E°L) were derived from the V°L versus temperature data determined experimentally. E°L values were negative, and their absolute values were found to increase with the chain length of fatty acid. The viscosities do not change appreciably with concentration at constant temperature while they do decrease considerably with temperature at a constant concentration. On the other hand, at a constant temperature and concentration, viscosities increased with increasing chain length.
There is a requirement to provide more efficient, sensitive, low-cost materials for remediation of contaminated water. Biochar as a sorbent is an effective and low-cost material to remove contaminants in water but its adsorption properties can be improved by impregnation of metals on the surface. In this study, a biochar derived from industrial tea waste was modified with Mg, Fe, Mn and Al salts to create different composites, which were tested for PO43− and Cd2+ sorption. The modifications created biochars with the (hydr)oxides of each metal and changed the characterization parameters and surface functionality. Cd2+ was efficiently removed by all the materials even at high Cd2+ loadings in the water (100 mg Cd2+ L−1), the biochar with Mg being the most efficient in Cd2+ removal. The biochar with Mg also achieved the best sorption of PO43−, sorbing up to 30% at 20 mg PO43− L−1. Tea waste biochar can be modified with metal salts to enhance inorganic pollutant removal from waters, especially with Mg salts.
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