Study on the desalination process and improvement effect of FGD-gypsum improving coastal saline-soil

To provide theoretical basis for the improvement of Shanghai coastal saline-soil, a soil column leaching experiment was carried out to study the process and improvement effect of soil desalination after soil applying 0.5%, 1%, 2.5%, and 5% mass ratio of FGD-gypsum, aimed at the characteristics of Shanghai coastal saline-soil. The result showed that, compared with the control, applying FGD-gypsum could increase soil saturated hydraulic conductivity by 5.1-6.5 times, increase leaching sodium quality by 11.0%-22.2%, decrease soil pH 0.41-0.11 units, decrease exchangeable sodium percentage (ESP) by 25.1%-76.7%. When FGD-gypsum improved the coastal saline-soil, the change rules of soil's physical and chemical properties were that, soil saturated hydraulic conductivity increased before leveling off, leaching sodium quality gradually increased, soil pH declined before leveling off, ESP reduced with increasing ratios of FGD-gypsum; soil leaching sodium ion concentration decreased sharply and then tended to equilibrium over time, and soil leaching out sodium was active in the first 2 days of leaching. In the process of FGD-gypsum speeding up soil desalination, soil leaching calcium quality and leaching sodium quality had relationship with soil hydraulic conductivity and the ratio of FGD-gypsum, and the leaching out sodium of FGD-gypsum-soil system was more accelerated when calcium ion concentration in soil leacheate was higher.