| In recent years, flue gas desulfurization gypsum (FGD-gypsum) as a soil amendment is popular for its low cost, large output, quick repair efficiency. Applying FGD-Gypsum to improve coastal saline soil is important for easing the condition of less land and more people,improving the quality of human life, improving the quality of ecological environment, and promoting a more healthy and sustainable development of economy in coastal area.FGD-gypsum is a by-product from flue gas desulphurization generated by power plants, steel plants, and other industries. And the FGD-gypsum from power plants and steel plants are very different because the compositions of the flue gases, the desulfurization process used, and the generated desulfurized raw materials are different. When FGD-gypsum used is different,whether the effect of FGD-gypsum improving saline soil is also different. Based on this knowledge, this study compared the use of two different types of FGD gypsum, one from a steel mill and one from a coal-fired power plant, to modify coastal saline soil.The purpose of this study in soil column experiment and field experiment are to explore that (1) desalting process, improvement effect and influencing factors of FGD-gypsum improving coastal saline soil, (2) the practical engineering effect of FGD gypsum improving coastal saline soil, (3)the change regulation of heavy metals in FGD-gypsum-soil system in the ecological safety of coastal saline soil improved by FGD-gypsum. And the main results are as follows:(1) The leaching sodium process of different types of FGD-gypsum improving coastal saline soil. In soil column experiment, different types of FGD gypsum-A and B were applied at the different dosages of quality (0%, 0.5%, 1%, 2.5%, 5%), and nine treatments were provided. The results showed that, both A and B gypsum could accelerate soil to leach sodium.When sodium was leached out, 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. The leaching out sodium of FGD-gypsum-soil system was more accelerated when the calcium ion concentration in soil leacheate was higher. Soil leaching sodium quality and leaching calcium quality had relationship with soil hydraulic conductivity and the ratio of FGD-gypsum. Gypsum B was superior to A at accelerating soil to leach sodium.(2) The influencing factors of FGD-gypsum improving coastal saline soil. In soil column experiment, both A and B gypsum could improve coastal saline soil. Compared with A, 13 could increase soil saturated hydraulic conductivity by 0.58-0.89 times, increase leaching sodium quality by 51.3%-74.0%, decrease soil leaching calcium quality by 3%-14%,increase soil permeability rate by 0.028-0.101 times, decrease soil pH by 0.10-0.36 units,decrease soil ESP by 66.7%-83.6%. For improving coastal saline soil, the improvement effect of B was superior than that of A due to higher Ca2+ dissolution efficiency and lower chloride ion content of B.(3) The field experiment of FGD-gypsum improving coastal saline soil. On the basis of soil column leaching experiment results, B which had better improvement effect was applied in the field experiment. The results showed that, B gypsum at the mass ratio of 0.5%, 1%,2.5%, and 5% could reduce soil pH to below 8.0 which was suitable for plant growth, reduced soil pH could be stability for a period of time, and there was no significant difference among the different dosages of FGD-gypsum (0.5%, 1%, 2.5%, 5%) (P>0.05). Applying B gypsum can reduce soil ESP, soil ESP was significantly reduced with increasing dosages of FGD-gypsum, also significantly reduced over time. Applying 2.5%, 5% mass ratio of B gypsum could reduce soil ESP to below 6%, which reached the ESP value of non-sodic soil.In the field experiment, B gypsum could have a good improvement effect for coastal saline soil.(4) The environmental risk of FGD-gypsum improving coastal saline soil. This paper emphatically researched the change regulation of heavy metals in FGD-gypsum-soil system.The results showed that As, Cd, Hg migrated easily to the depth of soil, that Cr was related to the redox state of the environment, that Pb stayed easily in the surface of soil, in FGD-gypsum-soil system.Overall, both A gypsum and B gypsum could improve coastal saline soil, B gypsum from a coal-fired power plant was superior to A from a steelworks for the improvement effect of coastal saline soil, due to higher Ca2+ dissolution efficiency and lower chloride ion content of B. And B gypsum could also have a good improvement effect for coastal saline soil in the field experiment. In the experiments, applying B gypsum to coastal saline soil had no environmental risk. This paper provides the basic data and related technical support for FGD-gypsum improving coastal saline soil, has important environmental significances. |
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