Characterization of Typical Biomass Ashes and Study on Their Potential of CO2 Fixation

With the increasing use of biomass resources, the recycling or disposal of biomass ash should be given more attention. An idea is put forward in this paper to study the possibility of CO2 fixation with biomass ash through the bicarbonation reactions of carbonate minerals. Four typical biomass resources, corn stalk, wheat stalk, cotton branch, and poplar, in a rural area of northern China, were sampled. Their ashes were thoroughly characterized for their chemical and mineral compositions through the joint adoption of three analysis tools, X-ray diffraction, X-ray fluorescence, and thermogravimetric analysis. It was found that the percentages of carbonates, such as CaCO3, K2CO3, MgCO3, etc., could amount to 25-40% by weight in the ashes of wheat stalk and corn stalk and to about 70% in the cotton branch and poplar. The high carbonate contents give them a theoretically good potential to absorb CO2 through bicarbonation reactions. Experiments of bubbling CO2 into solutions made from the ashes showed that 65-97% by weight of the carbonates could, in practice, be transformed into bicarbonates. This enhanced method can make the biomass ashes fix much more CO2 than they would under natural absorption conditions. Therefore, proper use of biomass ash may help to mitigate climate change in a distributed way if the fertilization process is improved.