Acidification characteristics and aluminum speciation in soil from mining and non-mining areas of Southern China

Objective  To perform comparative analysis of acidification characteristics and aluminum speciation of soil samples collected from mining and non-mining areas in Southern China, and provide a theoretical basis for the remediation of soil acidification in Southern China.

Method  Soil pH, organic matter content, exchangeable acid content, clay contents and cation exchange capacity (CEC) of 31 soil samples in Southern China were measured, and aluminum forms were examined by sequential extraction method. The correlation analysis and principal component analysis were applied to study the distribution of different aluminum species in soil of mining and non-mining areas.

Result  The contents of exchangeable hydrogen (Ex-H) (2.75 cmol·kg⁻¹) in mining soil were significantly higher than those in non-mining soil (0.97 cmol·kg⁻¹). The mining soil had significantly lower pH (H₂O) (3.44), CEC (6.34 cmol·kg⁻¹), clay content (13.05%), weakly organically bound aluminum (Al_Orw) (3.44 mmol·kg⁻¹) and organically bound aluminum (Al_Or) (12.96 mmol·kg⁻¹) contents than those in non-mining soil (4.39, 12.70 cmol·kg^–1, 28.64%, 8.32 and 41.46 mmol·kg^–1), respectively. For both mining and non-mining soil, the correlation analysis showed that exchangeable aluminum (Al_Ex) content had significantly negative correlation with pH (H₂O) (r=–0.577** and –0.671**), and Al_Ex content had significantly positive correlation with exchangeable acid quantum (Ex-Q) (r=0.927** and 0.662**), Ex-H (r=0.976** and 0.555*) and exchangeable aluminum (Ex-Al) contents (r=0.870** and 0.632**), respectively. The principal component analysis (PCA) showed that there were significant differences in soil acidification characteristics between mining and non-mining areas, and there were significant differences in the comprehensive characteristics of soil with different pH levels (pH<3.50, 3.50≤pH<4.50, 4.50≤pH<5.50 and pH≥5.50).

Conclusion  Compared with non-mining soils, mining soils have stronger acidity and lower content of organically bound aluminum. Non-mining soils have higher pH (H₂O), CEC and clay contents. The acidification characteristics of mining and non-mining soil are significantly different, and the acidification characteristics of soil with different pH gradients are also significantly different. Therefore, it is particularly necessary to improve soil pH and organic matter content in the remediation process of acidified soil of mining area.