Roles of soluble minerals in Cd sorption onto rice straw biochar

Investigating the potential of mineral precipitation in co-pyrolysis biochar: Development of a novel Cd (II) adsorption material utilizing dual solid waste

Ionic cadmium (Cd (II)) in water is a significant threat to ecosystems, the environment, and human health. Research is currently focused on developing efficient adsorption materials to combat Cd (II) pollution in water. One promising solution involves co-pyrolyzing solid residue from anaerobic digestion of food waste with oil-based drill cuttings pyrolysis residue to create a biochar with high organic matter content. This biochar has a lower heavy metal content and leaching toxicity compared to China's national standards, making it both safe and resourceful. It exhibits a high adsorption capacity for Cd (II) in water, reaching up to 47.80 ± 0.37 mg/g. Raising the pyrolysis temperature above 600 °C and increasing the amount of pyrolysis residue beyond 30 % enhances the biochar's adsorption capacity. The adsorption process is primarily driven by mineral precipitation, offering a promising approach for dual waste resource management and reducing heavy metal pollution.

Sorption and post-sorption performances of Cd, Pb and Zn onto peat, compost and biochar

The development of waste-derived sorbents to immobilize potentially toxic elements (PTEs) is a promising strategy, contributing to the achievement of sustainable development goals (SDGs). Therefore, this study aimed to assess the sorption performance of cadmium (Cd), lead (Pb) and zinc (Zn), comparing sorbents derived from organic fraction of municipal solid waste (composts and biochars) with peat. The physicochemical characterization, equilibrium of sorption, post-sorption analyzes and bioaccessibility were investigated. Results showed that the sorbents have distinct characteristics; however, each material have their particularities favorable to sorption. For instance, peat and composts have the highest cation exchange capacity (800-1100 mmol_c kg^-1), while biochar produced at 700 °C has the highest specific surface area (91.21 m² g^-1). The sorption equilibrium data revealed the actual sorption capacity and was well explained by the Freundlich and Langmuir isotherms and, in some cases, by the Dubinin-Radushkevich model. Post-sorption analyzes indicated the occurrence of several sorption mechanisms, driven by the physicochemical properties. Electrostatic interaction stood out for peat and compost. The FTIR spectrum for peat proved the complexation with oxygenated functional groups. The composts showed variations in the released cations (e.g. Ca²⁺ and K⁺), indicating cation exchange. Differently, for biochars, the XRD patterns showed that precipitation or coprecipitation seems to be one of the main mechanisms, especially for Cd and Pb. Regarding human bioaccessibility, the results of the gastric phase simulation (pH∼1.20) revealed lower percentages of Pb (33-81%) than Cd (91-99%) or Zn (82-99%), especially for the highest concentrations. Nevertheless, in numerical terms, all bioaccessible concentrations inspire care. In conclusion, among the sorbents, composts and biochars presented the best sorption performances and, therefore, have great potential for environmental applications. Furthermore, the bioaccessibility findings indicate that these assays, still little used in experiments with sorbents, are an important tool that should be better explored in the assessment of the environmental risk associated with contamination.

Corncob biochar combined with Bacillus subtilis to reduce Cd availability in low Cd-contaminated soil

Soil contamination by heavy metals such as Cd can pose a risk to the environment and human health. However, Cd is difficult to immobilize at low concentration levels in soil. Individually, Bacillus subtilis and biochar have been shown to be inefficient at immobilizing Cd in soil. In this study, corncob biochar was generated at different pyrolysis temperatures (300 °C-550 °C), and the Cd immobilization efficiency and performance of corncob biochar loaded with B. subtilis (CB@B) and corncob biochar alone (CB) were evaluated in solutions and in soil. The characterization (SEM and FTIR) of CB generated at different pyrolysis temperatures and CB generated at different pyrolysis temperatures in CB@B (300 °C-550 °C) indicated that a superior pore structure and abundant O-functional groups were obtained at a pyrolysis temperature of 400 °C for both CB@B and CB. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that the formation of Cd compounds was associated with the positive combined biosorption effect of the bacteria and biochar, electronic adsorption, activity of the O-functional groups (C[double bond, length as m-dash]O, COOH, OH, and Si-O-Si), and complexation between extracellular substances and Cd²⁺. Adsorption experiments were conducted in a solution to assess the effects of various operating parameters such as the time, pH, and adsorbent dose. The 400 °C-CB@B and 400 °C-CB samples achieved the largest reductions in the Cd concentration at 81.21% and 5.70%, respectively. Then, CaCl₂ extraction experiments were conducted in soil, and using 0.25%-CB@B, a 55.21% decrease was realized in the Cd concentration after 56 days and a 16.71% increase was realized in soil pH to 8.38. No significant difference was observed in the CB-treated groups, among which 1.0%-CB achieved the largest reduction of 26.08% after 56 days and a 3.20% increase in the soil pH to 7.41. The Tessier sequential extraction method obtained similar trends. Overall, 400 °C-CB@B demonstrated outstanding immobilization efficiency and durability, indicating that it provided a safe and nutrient-rich habitat for B. subtilis to realize a synergistic effect for Cd immobilization.

Screening the functions of modified rice straw biochar for adsorbing manganese from drinking water

The seasonal out-of-limit of manganese ions (Mn²⁺) in the drinking water reservoirs is an intractable problem to water supply, which can pose a threat to the human health. In this study, the removal of Mn²⁺ by using pristine (BC), pre-alkali (Pre-BC) and post-alkali (Post-BC) modified biochar originating from rice straw was investigated. The maximum adsorption capacities obtained for BC, Pre-BC, and Post-BC were 20.59, 28.37, and 8.06 mg g⁻¹, respectively. The Langmuir isotherm model and the pseudo-second-order kinetic model were suitable fitting models to describe the adsorption process. The investigation of adsorption functions was carried out that revealed that the predominant forces were precipitation and cation exchange with the proportions of 43.38–69.15% and 38.05–55.79%, respectively. With regard to precipitation, Mn(ii) particles (Al–Si–O–Mn and MnCO₃) and insignificantly oxidized insoluble Mn(iv) particles (MnO₂) were formed on the biochar surface. Alkali and alkaline earth metals facilitated the behavior of cation exchange, where the primary contributing ions for cation exchange were Na⁺, Mg²⁺ and Ca²⁺ during the adsorption process. These outcomes suggest that alkali pre-treated modification of biochar is practical for the application of manganese pollution control in lakes and reservoirs.

Modified biochar was used to remove Mn²⁺ from water with principal adsorption functions of precipitation and cation exchange. The MnCO₃ and Al–Si–O–Mn mainly driven precipitation and Na⁺, Mg²⁺ and Ca²⁺ primarily contributed to the cation exchange.