Attempts to obtain clean biochar from hyperaccumulator through pyrolysis: Removal of heavy metals and transformation of phosphorus.

The sound disposal of the ensuing heavy metal-rich plants can address the aftermath of phytoremediation. In this study, the first attempt was made to obtain heavy metals-free and phosphorus-rich biochar from phytoremediation residue (PR) by pyrolysis, and the effects of chlorinating agent type, chlorine dosage, and pyrolysis residence time on heavy metal removal, phosphorus (P) transformation, and biochar properties were investigated. The results showed that as chlorine dosage and pyrolysis residence time increased, added polyvinyl chloride (PVC) reduced the concentration of Zn in biochar to one-tenth of that in PR by intensified chlorination, where both Zn concentration (2727.50 mg/kg) and its leaching concentration (29.13 mg/L) met the utilization requirements, in which the acid-base property of biochar plays a key role in heavy metal leaching. Meanwhile, more than 90% of P in PR remained in biochar and the bioavailability of P in biochar enhanced with the decomposition of organic P to inorganic P, where the concentration of plant-availability P (Pnac) expanded from 1878.40 mg/kg in PR to 8454.00 mg/kg in biochar. This study demonstrated that heavy metal hyperaccumulator can be converted into heavy metal-free and phosphorus-rich biochar with promising applications, which provides new perspectives for the treatment of such hazardous wastes.

Enhancing production of hydrocarbon-rich bio-oil from biomass via catalytic fast pyrolysis coupled with advanced oxidation process pretreatment.

This study aims to propose a method for upgrading biomass pyrolysis products based on the combination of sodium persulfate pretreatment and fast catalytic pyrolysis. Combined with the analysis of components and thermogravimetric analysis, the result showed that after pretreatment the biomass structure was gradually depolymerized, the contents of lignin, the reaction of activation energy and the crystallinity of cellulose decreased. Due to the destructive effect of persulfate radicals, in fast pyrolysis, the relative contents of acids and oxygen-containing substances decreased, and the relative content of phenols can significantly increase to 19.20%. The yield of aromatic hydrocarbons and total hydrocarbons had a high value under the catalytic pyrolysis in the best performance which amount of yield reached 28.66% and 33.72%, respectively. Sodium persulfate pretreatment was beneficial in the production of hydrocarbon-rich bio-oils and high-value chemicals since the radicals can effectively depolymerize lignin which promoted the process of pyrolysis.