Abstract
Biocarbon is an attractive option to replace fossil carbon for metal production with the benefits of reducing greenhouse gas emissions and CO2 footprint. Nowadays, biocarbon is mainly produced from virgin wood through pyrolysis. As a carbon and energy-intensive industry, large amounts of biocarbon are needed in the metallurgical industry. With consideration of the increasing price of virgin wood and demands from other industries for this material source, it is necessary to broaden the biomass resource base. Woody biomasses with high carbon content and superior mechanical properties are still preferred for producing biocarbon. Therefore, various non-conventional woody biomasses are considered for biocarbon production, including forest residues, waste wood, etc. However, compared to virgin wood, the non-conventional woody biomasses often have high content of inorganic elements. During pyrolysis, the inorganic elements present in the feedstock might cause problems for the equipment and influence the reactions. A major fraction of the inorganic elements will remain in the produced biocarbon, which negatively affects the conversion of the biocarbon during metal production processes and some inorganic elements may influence the quality of the metal products as well. Demineralization is a process widely used for pretreatment of biomass materials that are rich in or contaminated with inorganic elements. Water leaching is still the most popular option as it is rather easy to conduct with low costs and fewer challenges for treating leachates. The objective of this paper was to compile and review the current literature concerning the demineralization of non-conventional woody biomasses through water leaching. The review revealed that leaching conditions (i.e., temperature and time) need to be carefully selected with consideration of the content and present form of the inorganic elements in different biomass materials. Moreover, the water leaching efficiency under given conditions is also related to the physical properties of the biomass material (i.e., particle size). In addition to the inorganic elements, the water leaching might also affect the organic composition (i.e., extractives) of the biomass materials. The properties of leached biomass materials should be characterized, which can be used for predicting the yield and quality of the produced biocarbon. Optimal water leaching procedures and conditions need to be identified and tested for maximizing the reduction of undesired inorganic elements and limiting the negative effect of properties of non-woody biomasses for biocarbon production.
