Removal of potentially toxic metal by biochar derived from rendered solid residue with high content of protein and bone tissue.

The purpose of this study was to produce rendering animal carcass residue char (RACR-C) by pyrolyzing the solid residues of low-recyclable rendered pig carcasses and to evaluate their cadmium (Cd) adsorption characteristics and mechanisms. As the pyrolysis temperature increased, the inorganic content of RACR-C increased, while the carbon content decreased. In particular, the surface structure and chemistry of RACR-Cs prepared at different pyrolysis temperatures were well described by SEM-EDS, XRD, XRF, TGA, and FTIR. The Cd adsorption characteristics of RACR-C were in good agreement with the Langmuir isotherm and pseudo-second-order models, and the Cd adsorption capacities of RACR-Cs prepared at various pyrolysis temperatures were in the order of RACR-C500 (73.5 mg/g)> RACR-C600 (53.8 mg/g)> RACR-C400 (41.5 mg/g) " RACR-C250 (15.9 mg/g). The intraparticle diffusion model suggested that the adsorption of Cd by RACR-C is greatly influenced by internal diffusion as well as external boundary. Since the Cd adsorption capacity of RACR-C is greatly influenced by the initial dosage, pH, and co-existing metals, it is necessary to manage these influencing factors when treating wastewater containing heavy metals. Our results suggest that Cd adsorption by RACR-C is a complex adsorption phenomenon by various mechanisms such as adsorption by functional group (CË­C and C-O), precipitation of Cd-P and ion exchange reaction by exchangeable cation occurring rather than by a single specific mechanism.

Exploration of the potential capacity of fly ash and bottom ash derived from wood pellet-based thermal power plant for heavy metal removal.

This study was conducted to explore the potential capacity for the removal of heavy metals from the fly ash (FA) and bottom ash (BA) emitted by wood pellet thermal power plants. Fly ash consists of inorganic compounds such as CaSiO3, P2O5, and K2O, whereas BA shows properties very similar to the biochar derived from organic biomass. The adsorption properties of both FA and BA for Cd were described well by the Langmuir and pseudo-second-order models, and the maximum adsorption capacity of FA for Cd was 4.2 times higher than that of BA. The results indicate that FA can be applied to the treatment of wastewater that contains heavy metals over pH range from 2-6; however, BA is considered to be most effective for application with wastewater that contains heavy metals at a pH of 5-6. Study of the mechanism concluded that the adsorption of Cd by FA is dominated by the formation of Cd2SiO4 complexes by chemical reactions between CaSiO3 and Cd ions as well as via the precipitation of Cd(OH)2 in the neutral and alkaline solutions that is caused by the dissolution of K. It was found that the adsorption of Cd by BA was influenced by the binding of functional groups (CC and COH), coupled CaCO3 dissolution-CdCO3 precipitation reaction and ion exchange between some minerals with Si and Cd ions in weakly acidic conditions. Results indicate that the FA and BA emitted from wood pellet thermal power plants have high potential for heavy metal removal, and their practical use in the purification and restoration of heavy metals could be an effective way to reduce the waste produced by power plants and clean the environment.