The Important Role of Biochar-Mineral Components in Adsorption Applications

Abstract

Biochar consisting of both carbon and mineral fractions is a porous carbonaceous material with a large specific surface area produced by the pyrolysis of biomass in closed containers, in an oxygen-free or limited oxygen environment [1]. Biochar, sometimes called agrichar, is obtained from the thermal decomposition of a wide variety of carbon-rich biomass materials such as grasses, hard and soft woods, and agricultural and forest residues [2]. Although biochar is generally used for improving soil fertility, increasing soil nutrient levels and water holding capacity, and reducing greenhouse gas emissions through carbon sequestration, it is suitable for adsorption of both organic (antibiotics, pesticides, dyes) and inorganic pollutants (nutrients, heavy metals). It has been used as a costly adsorbent [3-6]. Lately it has been demonsrated that biochar with minerals such as alkaline or earth alkaline metals have enormous effect on the final properties of the materials. Clay minerals are widely applied in agriculture and industrial engineering. A few of the important physical and chemical properties that make clay minerals valuable are particle size, surface chemistry, and surface area [7]. The negatively charged layers in the clay mineral are balanced by the hydrated exchangeable cations (Na+, Ca2+, Mg2+) in the interlayer space [8]. Clay minerals have a great potential to absorb various pollutants such as heavy metals, dyes and organic compounds through the cation exchange mechanism due to their high surface area and high ion exchange capacity [9,10]. It has been observed that biochar is less effective in removing pollutants from the aqueous medium by adsorption, compared to activated carbon, due to the characteristics of the extraction processes, its relatively low surface area and adsorption capacity [11]. Therefore, it has been observed that biochar composites prepared by impregnating biochar with specific materials such as clay minerals have been successfully used for the adsorption of organic and inorganic pollutants from water [6,12-14].