Hydrothermal carbonization of distillers grains with clay minerals for enhanced adsorption of phosphate and methylene blue

A novel one-pot synthesis method was developed to prepare modified hydrochar by co-hydrothermal carbonization of waste distillers grains using low-cost clay minerals (attapulgite or vermiculite). The loading of the clay minerals onto hydrochar surfaces altered the structure and surface composition of the hydrochar such that the clay-modified hydrochars showed better ability to adsorb methylene blue and phosphate in aqueous solution than the pristine hydrochar. The maximum methylene blue and phosphate adsorption capacities of the modified hydrochar reached 340.3 and 96.9 mg g^-1, respectively, comparable or higher than that of many commercial sorbents. Multiple mechanisms, including electrostatic attraction, ion exchange, complexation, and physical adsorption, controlled the adsorption process. These results highlight excellent potential for distillers grains-derived hydrochar-clay composites as an environmental sorbent, capable of removing a variety of contaminants from aqueous solutions.

One-pot synthesis and characterization of engineered hydrochar by hydrothermal carbonization of biomass with ZnCl2

Hydrochar, the product of hydrothermal carbonization of biomass, is a sustainable alternative to other carbonaceous environmental sorbents. However, its use has been limited due to its low surface area. A one-pot biomass/metal salt co-hydrothermal synthesis method might improve its sorptive properties while retaining its efficient production characteristic. Thus, bamboo sawdust and zinc chloride (ZnCl₂) were combined in a hydrothermal reactor (200 °C, 7 h) for preparing modified hydrochar. Compared to the non-modified hydrochar, the hydrochar produced with the addition of ZnCl₂ during hydrothermal treatment was more fully carbonized (C content increased from 54% to 64%), of higher surface area after acid washing (30 versus 1.7 m² g^-1), and enriched in O-containing functional groups and of greater aromaticity (according to FTIR and XRD analysis). Because of these improved properties, Methylene blue adsorption capacity of the modified hydrochar increased by nearly 90% and by 257% after it was rinsed with acid. This study highlights the potential of this one-pot co-hydrothermal treatment of biomass in presence of metal salt to provide a simple and effective hydrochar with properties suitable for environmental remediation and water treatment.

Immobilization of heavy metals in contaminated soils by modified hydrochar: Efficiency, risk assessment and potential mechanisms

The modified hydrochar was prepared by a facile one-pot lime-assisted hydrothermal synthesis approach and the modified hydrochar and pristine hydrochar were investigated to immobilize the heavy metals (HMs) of Pb and Cd in contaminated soils. The results showed that the modified hydrochar exerted significantly enhanced effectiveness in immobilizing Pb and Cd comparing to pristine hydrochar, resulting from the increased surface functionality and non-crystalline properties, increased pH value and enhanced electronegativity of hydrochar. By introduction with 5% modified hydrochar, the contaminated soils showed the highest value of 34.5% (Pb) and 8.1% (Cd) reductions in leaching toxicity, and significant improvements of 95.1% (Pb) and 64.4% (Cd) were observed. In addition, the concentrations of acid soluble fraction were remarkably reduced by 54.0% (Pb) and 27.0% (Cd), and the reductions were much higher than that of 29.5% (Pb) and 8.3% (Cd) for 5% pristine hydrochar treatment. The enhanced surface complexation, precipitation and cation-π interaction played an important role in the immobilization of HMs in soils. The present study offered a novel and cost-effective approach to prepare soil amendment from waste biomass towards HMs immobilization in contaminated soils.