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Abstract Biochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.

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The exploitation of coal and metallic mineral resources worldwide invariably results in the production of large quantities of overburden, gangue, and tailings materials containing significant amounts of sulfide minerals. These sulfide minerals, which include sphalerite, chalcopyrite, galena, and other complex sulfides, are often disseminated in pyrite, which is the most abundant sulfide mineral in the earth's crust. Once exposed to water and oxygen through mining and mineral processing operations, these sulfides become immediately susceptible to chemical and biochemical oxidation with the consequent production of highly acidic, metal‐laden leachates, which are generally referred to as acid rock drainage (ARD) or acid mine drainage (AMD). This ARD production, which can be sustained for hundreds of years, has become the single biggest environmental problem facing the mining and mineral industry. Untreated acid rock drainage leads to serious contamination of large areas of land, as well as surface and ground water resources. The seriousness of the problem has led to major research efforts to find solutions. However, effective ARD treatment and prevention solutions have eluded the scientific community over the past decades. This paper presents a detailed review of the current state of scientific knowledge with regard to the magnitude of the problem, the chemistry and mechanism of sulfide mineral oxidation and ARD formation, the role of microorganisms in ARD formation process, and the proposed approaches for the treatment, control, and prevention of ARD formation. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

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The adsorption of hexavalent chromium [Cr(VI)] onto bone char was optimised as a function of pH, initial Cr(VI) concentration, and bone char dosage using aqueous solution in batch tests. The initial Cr(VI) concentrations were varied between 5 and 800 mg/L to investigate equilibrium, kinetics, and the adsorption isotherms. About 100 % of Cr(VI) was removed at initial pH of 1.0 with initial Cr(VI) concentration of 10 mg/L, using 2 g of bone char after 2 hours. The maximum adsorption capacity of the bone char was 4.8 mg/g for an initial Cr(VI) concentration of 800 mg/L. The adsorption kinetics of Cr(VI) onto bone char followed a second order kinetic model. The adsorption isotherm followed the Langmuir model for Cr(VI) adsorption. In general, bone char demonstrated promising results as an effective adsorbent for removal of Cr(VI) from the aqueous solution. The results from this study could be useful in designing a filtration unit with bone char as the adsorbent in a full-scale water and wastewater treatment plant for the removal of Cr(VI) from contaminated water.