Effect Of Mineral Addition On Carbon Sequestration,emission Reduction And Stability Of Biochar

The use of pyrolysis technology to fix carbon in biomass in the form of stable carbon and store it in soil is a means to achieve carbon sequestration,which is of great significance to achieve carbon sequestration and emission reduction.The development of biochar with high carbon sequestration rate and high stability is of great theoretical and practical significance for biomass resource utilization and achieving carbon emission reduction.Mineral modification treatment can play a dual role in regulating carbon sequestration and emission reduction as well as stability of biochar,but there are few studies on the modification of natural minerals such as zeolite,calcium hydroxide and montmorillonite.Therefore,in this paper,natural minerals such as zeolite,calcium hydroxide and montmorillonite.were first used to modify sewage sludge biochar,carbon retention rate and physicochemical properties of biochar were analyzed,FTIR and XRD were combined to reveal its influence mechanism.Secondly,the mineral with the best regulatory effect was selected and applied to the modification of biomass from industry,animal husbandry,forestry and agriculture,represented by sewage sludge,cow dung,pine sawdust and maize straw,to investigate its influence on carbon sequestration performance and its mechanism of action.At the same time,chemical oxidation and thermogravimetric analysis were used to explore the influence of minerals on the stability of biochar.Finally,different biochar modified with calcium hydroxide was applied into the soil to explore the influence on greenhouse gas emissions（CO₂and CH₄）from soil carbon sources.The main research results are as follows:（1）Zeo-SSBC,Ca-SSBC,Mon-SSBC,and Mix-SSBC have good carbon fixation performance.The mineral modification increased the yield,ash content and pH value of biochar.Calcium hydroxide has the best carbon sequestration effect on sewage sludge biochar,montmorillonite and zeolite have similar effect,and the carbon sequestration effect of mixed minerals is not as good as that of single minerals.At the pyrolysis temperature of 300℃,the carbon retention rates of Zeo-SSBC,Ca-SSBC,Mon-SSBC and Mix-SSBC increased by7.30%,12.02%,6.97%and 8.75%,respectively,compared with SSBC.The modification of minerals can promote the formation of CO₃^2-functional groups in biochar and the changes of C-O-C,C-O,C=C,C=O and other functional groups.Ca CO₃crystals and minerals can form protective barriers with biomass or fill biochar to increase the retention of carbon in the form of inhibiting carbon decomposition,thus improving the carbon fixation performance of biochar.（2）Calcium hydroxide minerals can significantly promote the carbon sequestration effect of different biochar（SSBC,CDBC,PSBC,MSBC）in sewage sludge,cow dung,pine sawdust and maize straw.The yield,ash content and pH value of biochar were increased after calcium hydroxide modification.At the pyrolysis temperature of 500℃,the carbon retention rates of Ca-SSBC,Ca-CDBC,Ca-PSBC and Ca-MSBC increased by 8.88%,13.63%,28.27%and10.94%respectively compared with unmodified biochar.The modification of calcium hydroxide promoted the conversion of carbo-oxygen functional groups into unsaturated aromatic substances,and generated CO₃^2-functional groups and aromatic C-H bonds,which improved the carbon fixation performance of biochar and enhanced the stability of biochar.（3）Chemical oxidation tests showed that the physical barrier formed by calcium carbonate crystals and the protective effect of organic mineral complex formed during the interaction between minerals and biochar enhanced the chemical stability of biochar.In addition,the carbon content of biochar modified by calcium hydroxide increased compared with that before oxidation because calcium adsorbed and fixed carbon dioxide in the air.In addition to the very stable SSBC（stability coefficient R50≥0.7）,the addition of calcium hydroxide improves the thermal stability of CDBC,PSBC and MSBC from medium stable(R₅₀from 0.57-0.66)to very stable(R₅₀from 0.73-0.90),which enhances the thermal stability of biochar.Moreover,the carbon sequestration potential（CS）of SSBC,CDBC,PSBC and MSBC increased from 29.43%-37.89%to 33.06%-51.30%by the modification of calcium hydroxide,showing considerable carbon sequestration potential.（4）Biochar modified by calcium hydroxide significantly inhibited soil CO₂emission,and the inhibition effect was enhanced with increasing amount of addition.Compared with CK,adding 5%Ca-SSBC,Ca-CDBC,Ca-PSBC and Ca-MSBC can reduce the cumulative CO₂emissions by 48.60%,46.39%,61.62%and 56.56%,respectively.Except for the addition of 1%Ca-MSBC,the combined warming potential（GWP）of calcium hydroxide modified biochar was smaller than that of CK sample.When the addition amount was 5%,the GWP values of Ca-SSBC,Ca-CDBC,Ca-PSBC and Ca-MSBC are reduced by 45.33%,37.34%,56.36%and 53.06%,respectively,compared with CK sample.It can be seen that the return of biochar from biomass modified by calcium hydroxide to the field is a new way of solid waste management that can effectively reduce emissions.