Effects of modified coal gangue on the physical structure and organic carbon components of Shajiang black soil
This study explores the impact of modified coal gangue on the shrinkage characteristics,soil organic carbon(SOC),and its components in Shajiang black soil.Coal gangue was first processed into three particle sizes(0-2,2-5 mm,and 5-8 mm),and subjected to modification by soaking for two hours at 75℃in 3%sodium hydroxide(NaOH)and at 70℃in 5%hydrochloric acid(HCl)solutions,respectively,producing alkali-modified and acid-modified variants.Both the original and modified forms of coal gangue were characterized structurally.Subsequent laboratory incubation experiments with Shajiang black soil assessed alterations in soil bulk density(ρb),total porosity(φ),micro-pore characteristics,shrinkage behavior,and soil organic carbon components.The results showed that:Alkali-modified and acid-modified coal gangue significantly decreased ρb by 25.60%-38.69%and 26.19%-35.71%,respectively,compared to the control,and 1.57%-5.50%and 0.85%-2.36%compared to unmodified coal gangue.φ increased by 44.34%-67.02%and 45.38%-61.88%,respectively,compared to the control,with minor increments of 1.34%-3.84%and 0.65%-2.19%compared to the unmodified treatment,respectively,Moreover,a general decrease in micro-pore volume and an increase in their average diameter were observed.The overall trend for soil coefficient of linear extension was:control>5～8 mm coal gangue>2-5 mm coal gangue>5-8 mm acid-modified coal gangue>5-8 mm alkali modified coal gangue>0-2 mm coal gangue≈2-5 mm acid-modified coal gangue>2-5 mm alkali-modified coal gangue>0-2 mm acid-modified coal gangue>0-2 mm alkali-modified coal gangue,with the shrinkage showing a consistent overall trend with coefficient of linear extension.SOC,dissolved organic carbon(DOC),readily oxidizable organic carbon(ROC),and microbial mass carbon(MBC)content increased by 103.19%-328.88%,98.23%-470.50%,100.00%-279.90%and 85.88%-347.53%,respectively.As the particle size of coal gangue increased,ρb and carbon component content generally showed a decreasing trend,while coefficient of linear extension and shrinkage showed an increasing trend.Structural equation modeling highlighted soil shrinkage characteristics as a critical determinant in the accumulation of soil organic carbon components.In conclusion,modifications through both alkali and acid treatment enhanced the soil's physical structure and organic carbon content,with alkali modification showing more pronounced improvements,especially at smaller particle size.The optimal modification identified was the addition of 0-2 mm alkali modified coal gangue.These results provide a theoretical foundation for enhancing the physical and organic properties of Shajiang black soil in the Huaibei region.
modified coal gangueShajiang black soilphysical structureorganic carbon component
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