Co-pyrolysis of rice straw with industrial wastes: waste disposal and environmental remediation

Abstract

To reduce waste volumes and recover valuable products, char was synthesized via co-pyrolysis of rice straw (RS) with spent tires, sulfur wastes, and CO2. The inclusion of wastes and CO2 in pyrolysis of RS was hypothesized to enhance the sorption ability of char for various contaminants, including 2,4-dinitrotoluene (DNT), 2,4-dichlorophenol (DCP), lead, barium, chromate (CrO42-), and selenate (SeO42-). Using a lab-scale electrical furnace, the co-pyrolysis was conducted, and the soprtion capacity of char was evaluated via a series of batch sorption experiments. The maximum sorption capacity of spent tire-RS char for DNT was 16.8 ± 0.2 mg g-1, much higher than that of RS biochar (10.1 ± 0.3 mg g-1) due to increasing carbon content from the spent tires. The sorption of DCP to the spent tire-RS char was also enhanced via hydrophobic sorption to carbon residues, although not to the same degree of DNT due to deprotonation of the DCP. Compared with RS biochar, co-pyrolysis with raw sulfur wastes and CO2 enhanced sorption of lead, barium, and chromate, which can be attributed to increased cation and anion exchange capacities resulting from developments of oxygen or sulfur-containing functional groups. Sorption of selenate was strongly affected by pH. The results suggest that co-pyrolysis of agricultural and industrial wastes and CO2 is a promising option for the final waste disposal and the production of valuable char, which can be selectively customized for various types of contaminants as sorbents.