Enhancing Soil Aggregation and Water Retention by Applying Kaolinite Clay to Post‐Tin‐Mined Land on Belitung Island, Indonesia

Post-mining sandy soils have low water retention, which causes soil particle separation and persistent soil erosion. Although organic matter is commonly used for soil restoration, it is lightweight, washes away during heavy rain, and decomposes under strong sunlight. The high potential for extreme rainfall events in tropical regions poses significant challenges to restoration projects. Therefore, we investigated the impact of kaolinite clay particles on enhancing soil stability in post-mining sandy soils. Soil samples were collected from three sites representing different succession stages of post-mined land (0, 1, and 6 years since mining cessation) and an adjacent natural forest as the reference site on Belitung Island, Indonesia. Soil samples were treated with 1% or 5% kaolinite or left untreated (control) and incubated at 34°C to mimic the local conditions of the study area. The samples were then analyzed to determine the soil aggregate distribution, water holding capacity, and soil erodibility, and SEM imaging was performed to examine the soil particle morphology. The results revealed an increasing trend in the silt-sized aggregate content and a 2%–5% increase in water retention in the 6-year soils relative to the untreated soils. The highest water retention was observed in the 6-year post-mining soil sample. Kaolinite amendment significantly reduced soil erodibility by 40%–50% compared to the untreated soils, even in the early restoration period (0–1 year post-mining). Kaolinite improved soil aggregation and water retention in post-mining sandy soils while reducing soil erodibility—highlighting its potential for accelerating land restoration in mining-affected areas.