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Response of water-soluble salt accumulation in weathered gneiss spoil substrate to the addition of superabsorbent polymer under a semiarid climate

Sun, Yongkang, Zhao, Tingning, Zhang, Yan, Ma, Deli, Yang, Jianying
Journal of soils and sediments 2020 v.20 no.1 pp. 190-203
absorption, bulk density, calcium, chlorides, ecological restoration, electrical conductivity, environmental factors, evaporation rate, gneiss, ions, lawns and turf, magnesium, mine spoil, mining, pH, remediation, semiarid zones, sodium, soil water, soluble salts, sulfates, super absorbent polymers, water holding capacity, water solubility
PURPOSE: Superabsorbent polymer (SAP) has been widely used to improve soil moisture conditions in the ecological restoration of mining land. The effect of SAP on water-soluble salt movement in SAP-modified gneiss spoil in a semiarid region was studied in this experiment. MATERIALS AND METHODS: Weathered gneiss spoil, dress soil, SAP, and turf were mixed via the L₂₅(5⁶) orthogonal test, and the semiarid environmental conditions were controlled for 1 year in a climate chamber. RESULTS AND DISCUSSION: The results showed that bulk density, field water-holding capacity, and daily average evaporation rate of the substrate were dominated by the proportions of the soil and turf contents but were not significantly influenced by the SAP. The water-soluble salt in the top layer of the substrate increased significantly as the SAP concentration increased; i.e., it increased by 36.5% per 0.1% increase in the SAP within the range of 0 to 1%. The major ions influenced by the SAP were Na⁺, Mg²⁺, Ca²⁺, Cl⁻, and SO₄²⁻. The SAP decreased the pH of the substrate before the experiment, but only the top layer was influenced by the increase in the SAP after 1 year. The electrical conductivity (EC), which reflects the content of soluble ions in different substrate layers, was significantly influenced by the SAP in the following order: EC-middle layer < EC-bottom layer < EC-top layer. CONCLUSIONS: Based on the above results, we can conclude that the strong water and salt ion absorption ability of the SAP may limit the leaching of water-soluble ions and aggravate the accumulation of surface salts under semiarid environmental conditions. This study will be helpful for understanding the salt accumulation caused by the use of SAP in the remediation of mine spoil with high soluble salt contents.