A review of lignocellulosic biochar modification towards enhanced biochar selectivity and adsorption capacity of potentially toxic elements

Abstract

Biochar, which is rich in aromatic carbon and minerals, is a product of biomass pyrolysis at temperatures ranging from 350°C to 1000°C in oxygen-limited environments. In recent years biochar has generated much interest in the field of water treatment in view of low production costs, availability of the feedstock (e.g. lignocellulosic biomass waste) and adsorptive properties. This review incorporates researches on artificial and natural modifications of biochar towards adsorption of potentially toxic elements on biochar. The aim of this study was to provide a comprehensive review of recent research findings and theory developments on the existing modifications of biochar for adsorption of potentially toxic elements (i.e. inorganic compounds) from aqueous solutions. Factors affecting adsorption of potentially toxic elements by lignocellulosic biochar and modification techniques for lignocellulosic biochar towards enhanced adsorption of potentially toxic elements were analyzed. The novelty of this study is discussion of the natural modifications of biochar and smart properties of biochar towards adsorption of potentially toxic elements. Recommendations are offered for modifying the lignocellulosic biochar to produce designed, engineered or smart biochar with high adsorption capacity for potentially toxic elements. Key words: engineered biochar; adsorption; lignocellulosic biomass; pyrolysis IntroductionAccording to European Biochar Certificate 2015, biochar 'is a heterogeneous substance rich in aromatic carbon and minerals. It is produced by pyrolysis of the sustainably obtained biomass under controlled conditions with clean technology and is used for any purpose that does not involve its rapid mineralization to CO2 and may eventually become a soil amendment'. At the beginning of biochar research, it aroused much interest as a soil amendment because of its potential for carbon sequestration and soil quality improvement. After physical, chemical and biological properties of biochar (Sun et al., 2014) and production technologies (Nartey and Zhao, 2014) were investigated, biochar research shifted from soil improvement to application in health sciences and engineering. Biochar could be a new low-cost adsorbent for removal of inorganic compounds (e.g. potentially toxic elements). It can be produced from wastes (e.g. lignocellulosic biomass) and is cheaper than activated carbon because it is produced through single-stage pyrolysis at 350-1000 °C and does not need additional costs in the activation process. Activation is the second stage in the production of activated carbon and occurs in the temperature range of 600-1200 °C in the presence of oxidizing gas, e.g. CO2 or steam, which results in the formation of a well-developed micropore structure. Therefore, biochar requires less energy for production than activated carbon (Azargohar and Dalai, 2006) and can be used as an alternative adsorbent to remove potentially toxic elements (PTE) from water solutions and air (Baltrėnaitė et al., 2016a). It demonstrated the ability ...

Biochar-based materials and their applications in removal of organic contaminants from wastewater: state-of-the-art review

“…The author attributed the significant modification in morphological and physical-chemical properties to the synergetic effect of the CEM method. Despite above CuCl 2 and MgCl 2 , various metallic salts, such as AlCl 3 , CaCl 2 , MnCl 2 and ZnCl 2 , have also been widely used to pretreat biomass in the production of biochar-based metallic oxides/ hydroxide composites (Wang et al 2018b;Fang et al 2015;Wang et al 2015c;Chemerys et al 2018;Li et al 2018e). The resulting composites usually exhibit dramatic changes in morphological and physical-chemical properties, leading to better performance in environmental treatment.…”

Potential Use of Biochar from Various Waste Biomass as Biosorbent in Co(II) Removal Processes

“…Thus, it can be observed that mustard waste biomass and soy waste biomass required a high pyrolysis temperature (650 • C) compared with algae waste biomass (600 • C). This can be explained if the biomass of algae waste is considered to have a low content of cellulose and hemicellulose [34], and therefore the temperature required to carbonize the protein molecules in its structure is lower. However, it should be noted that in the mentioned pyrolysis conditions, the mass decrease is higher than 40% and the order is: Mustard waste biomass > soy waste biomass > algae waste biomass.…”

Impact of Biomass Sources on Acoustic-Based Chemical Functionalization of Biochars for Improved CO2 Adsorption

“…The ash generated during pyrolysis remains trapped inside the pores of the biochar, thus lowering the surface area . The surface area trend can be further explained as based on the following explanation: lignocellulose contains hemicellulose (40–50%), cellulose (20–40%), and lignin (10–40%) . Decomposition of hemicellulose takes place mainly at 250–350 °C, followed by cellulose at 325–400 °C and lignin at 300–550 °C .…”

“…The surface area trend can be further explained as based on the following explanation: lignocellulose contains hemicellulose (40–50%), cellulose (20–40%), and lignin (10–40%) . Decomposition of hemicellulose takes place mainly at 250–350 °C, followed by cellulose at 325–400 °C and lignin at 300–550 °C . Thus, biochars composed of cellulose and hemicellulose decompose easier and possess higher surface areas .…”