Mechanisms and Environmental Applications of Biochar for Heavy Metal Remediation in Contaminated Soils

Environmental applications of agricultural waste-derived biochars for soil improvement and lead adsorption

Biochar, a carbon-rich  material produced by the pyrolysis of organic waste, has emerged as a low cost and sustainable material for several environmental applications including the enhancement of soil fertility and adsorption of heavy metals. This study evaluated and compared the potential of four plant-based biochars (wheat straw, pine straw, corn cob and parthenium biochars) for environmental applications by analyzing their physicochemical properties. The results showed that of all the analyzed biochars, parthenium biochar was found to be most effective in enhancing soil fertility as it contained the highest total organic carbon (79.50 %) and N contents (2.50 %). Moreover, the concentration of toxic heavy metals was found below safe limits in all the biochars studied in this research which favors their suitability for environmental applications. On the other hand, adsorption studies revealed that the corn cob biochar exhibited the highest lead removal efficiency (98 %) at an adsorbent dose of 2 g l1. Based on these findings, it is concluded that the agricultural waste-derived biochars can be used as sustainable and effective materials for environmental management, including soil quality enhancement and heavy metal remediation. 

Biochar Production: Toward Safe, Effective, and Sustainable Agriculture

Biochar, a carbon-rich product resulting from the thermochemical transformation of organic biomass under limited oxygen condition, is currently drawing much worldwide attention due to its multiple applications in carbon sequestration, soil improvement, environmental remediation, and biomass waste management. Initially, the focus of research was primarily on the technical possibilities of biochar production, its economic aspects, and its contribution to climate change mitigation through carbon sequestration and the promotion of sustainable agriculture. Nevertheless, recent research indicates the high complexity and dynamics of biochar interactions with the environment, driven by a combination of factors like feedstock type, process conditions, biochar properties, and other factors. While biochar exhibits multiple beneficial effects, including improving soil structure, enhancing nutrient retention, promoting microbial activities, and remediating contaminants, several environmental risks associated with biochar application have also been identified, namely the formation of polycyclic aromatic hydrocarbons (PAHs), heavy metal contamination, creation of persistent free radicals, changes in soil chemistry, and modification of soil microbial community structure. Such risks are greatly related to production process parameters, treatment methods, and biochar application practices. Moreover, differences in feedstock choice, pyrolysis temperature, reactor design, biochar application rate, and analytical methods used make comparative analysis of results difficult.

Synergistic remediation of cadmium-contaminated soil by biochar-cement-plant system: performance and underlying mechanism

Metal oxide‐loaded biochar for heavy metal removal from water on synthesis, mechanisms, and future perspectives

Heavy metal water pollution poses severe health risks to humans. Heavy metal contamination from natural and anthropogenic sources poses a serious threat to the environment. Various techniques including adsorption, ion exchange, precipitation, chemical reduction, and ultrafiltration have been employed to remove heavy metal ions from wastewater. Adsorption is frequently preferred due to its simple operation and good controllability. Metal oxide‐loaded biochar has unique properties and is a highly attractive adsorbent due to its low cost and good sustainability. In this review, the preparation methods and classification of metal oxide‐loaded biochar are first thoroughly described. The characterization approaches, including instrumental analysis and chemical analysis, are further introduced in detail. Adsorption kinetics, isotherms, and thermodynamics are discussed to elucidate the removal processes and mechanisms. Particular emphasis is placed on the mechanisms of physisorption and chemisorption. Furthermore, this review evaluates the application potential of metal oxide‐loaded biochar and analyzes key future research challenges in this field.

Chemical Stabilization and Enhanced Phytostabilization of Heavy Metal Contaminated Acidic Boreal Forest Soils using Biochar and Modified Biochars

Heavy metal contamination in acidic boreal forest soils is a significant environmental concern due to the enhanced mobility and bioavailability of metals under acidic conditions. Biochar treatments have gained increasing attention as sustainable remediation materials because of their ability to immobilize heavy metals and improve soil properties. This research evaluated the effectiveness of biochar (BC) and chemically modified biochar for the chemical stabilization and enhanced phytostabilization of cadmium (Cd), copper (Cu), and Zinc (Zn) in acidic multi-metal-contaminated boreal forest soils under moderately and highly contaminated conditions. The first study evaluated the effectiveness of BC and chemically modified biochar, including NaOH-modified biochar (NBC), H2O2-modified biochar (HBC), and KMnO4-modified biochar (KBC), in reducing metal mobility and improving metal stability in acidic contaminated soils. Adsorption experiments, incubation studies, leachate monitoring, toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), available metal extraction, and sequential fractionation analysis were conducted to assess amendment performance. Chemically modified biochar of NBC and HBC demonstrated greater adsorption capacity and immobilization efficiency than BC. Biochar treatments significantly reduced available and leachable Cd, Cu, and Zn concentrations while increasing soil pH and promoting redistribution of metals from more labile fractions to more stable forms. Although KBC showed the highest adsorption capacities in batch experiments, its stabilization performance under soil conditions was not consistently superior. The second study evaluated the effectiveness of BC and HBC in biochar-assisted phytostabilization using Canada wild rye (Elymus canadensis), little bluestem (Schizachyrium scoparium), and switchgrass (Panicum virgatum). A three-month growth chamber study was conducted to assess dry matter production, metal accumulation in roots and shoots, available metal concentrations, soil pH, and heavy metal stability in phytostabilized soils. Both BC and HBC improved phytostabilization performance by reducing Cd, Cu, and Zn mobility and accumulation in plant tissues while improving metal stability in soil. However, BC produced greater dry matter and showed comparable or greater effectiveness than HBC in reducing metal uptake and translocation in native grasses. Biochar treatments also increased soil pH and reduced TCLP and SPLP extractable metal concentrations, indicating lower metal leaching potential in phytostabilized soils. Overall, the findings demonstrated that biochar treatments effectively reduced heavy metal mobility, availability, and leachability in acidic boreal forest soils. Chemically modified biochar, particularly NBC and HBC, showed greater potential for chemical stabilization, while BC demonstrated stronger overall performance for biochar assisted phytostabilization. These findings highlight the potential application of biochar treatments as sustainable remediation strategies for acidic Cd, Cu, and Zn contaminated boreal forest soils.

Green technologies for soil remediation: a systematic review

Heavy metals, petroleum hydrocarbons, microplastics, and pesticides exhibit mutagenic, carcinogenic, immunotoxic, and teratogenic properties, leading to significant changes in the soil’s physical, chemical, and microbiological characteristics. This poses a substantial threat to overall ecosystem health. Consequently, addressing soil contamination requires the prompt adoption of sustainable physico-chemical and bio-based remediation approaches. This review provides a systematic analysis of current soil remediation methods that utilise green technologies. Particular attention is given to phytoremediation techniques, the use of soil conditioners such as biochar, hydrochar, and biopolymers, as well as the application of layered double hydroxides. The mechanisms by which these technologies mitigate pollutants such as heavy metals, organic contaminants, and nutrients are analysed, highlighting their role in enhancing soil health while minimising ecological impact. By integrating these green approaches, sustainable soil remediation can be achieved, supporting environmental restoration and agricultural productivity. This review offers valuable insights for researchers and policymakers in advancing eco-friendly soil rehabilitation strategies.