Efect Of FGD-gypsum On Improving Heavy Soda-saline Soil And On Agricultural Environment

For improving the heavy soda saline soil in Datong with desulfurization gypsum safely,a soil column leaching experiment was carried out for getting the desalination laws under five levels of FGD-gypsum(0,5.5,11,22 and 33 g/kg)applying into the 0-20cm surface layer of the tested soil,and several ions in leachate was also tested,such as Na+,Ca2+,CO32-,and SO42-.At the same time,a pot experiment was coducted to estimate the effect of different rates of FGD-gypsum(0,15,22.5 and 30 t/hm2)on pH and on EC of soil,and growth of forage maize.Concerning heavy metals might bring environment problem to soil,this experiment also investigated the leachate of heavy metals(As,Hg,Cd and Ni)and the accumulation of those in different soil layers.Then forage maize and soil were evaluated potential environmental risks from heavy metals pollution after continuous FGD-gypsum application for a few years.The main results were as follows:1.FGD-gypsum accelerated soil salt leaching,main salt ions in soil showed the process of desalination.The leacheate of the control was not collected.Soil hydraulic conductivity had enhanced,Na+ leaching had improved obviously,and soil pH decreased after contacting and leaching.The leaching amount of Na+ had significant negative correlation with leaching time(P<0.05),the leaching amount of Ca2+ and SO42-appeared a peak in thirtieth day,and the leaching amount of CO32-was positively correlated with time(P<0.05).The amount of Na+ and CO32-,and pH fell sharply,Ca2+ and SO42-had improved significantly in 0-20 cm soil horizons,surface soil of that was the best leaching efficiency.Soil pH and soil horizons was positively correlated with time(P<0.05,r=0.85).The effect of improvement did not have positive correlation with FGD-gypsum application rates,and the best application requirement was 22 g/kg for improvement efficiency.2.It showed that heave metals(As,Hg,Cd and Ni)leaching were improved by applying FGD-gypsum comparing to the control.The leaching amount of heave metals at 33 g/kg of FGD-gypsum was significantly higher than that at 5.5 g/kg in the beginning of 20 days,and then it was not significant difference at different proportions FGD-gypsum later.The amount of As and Hg gradually increased as leaching time increased,on the contrary,the amount of Cd and Ni gradually decreased.The amounts of Hg and Cd in soil were not detected with FGD-gypsum application.With the soil deepen,the variation of As content in soil was not obvious,and Ni accumulated in bottom soils of the experiment.The amounts of As and Ni in 0-20 cm horizons had no significant accumulation with FGD-gypsum consumption.According to the second grade of the Standard of Soil Environmental Quality,the contents of the heave metals(As,Hg,Cd and Ni)in the experimental soils were well complied with the Environment Quality Standard.3.Results indicated that EC of soil increased,and pH of soil decreased significantly with applying the FGD-gypsum.The raise ratio of germination rate and of forage maize stem diameter were up to 55%and 21%,respectively.Plant height and root length decreased,while the crop yield enhanced comparing to the control.Excessive FGD-gypsum consumption inhibited the growth of forage maize.In the experiment,15 t/hm2(?g/kg)of FGD-gypsum was favorable for crops growth.4.It was observed that concentrations and characteristics of heavy metals were differences in stem,root of forage corn and soil under the different dosage of FGD-gypsum.It increased the content of Cd,Hg in forage corn straw and root system,while As and Ni contents did not change significantly.Compared to the control,As and Ni bioconcentration factors got smaller,Hg got larger under 22.5,30 t/hm2 of FGD-gypsum application,and Cd was not obvious.The relativity between the heavy metals contents in stem and in root and that of soil was not obviously.5.The index of geo-accumulation and potential ecological risk was used to evaluate the ecological risk of heavy metals pollution.The cumulative degree of As in potting soil was low-level with no pollution degree.The content of Hg and Ni in potting soil increased with the increasing FGD-gypsum application,which indicated that pollution degree became heavy.The potential ecological risk was Cd>Hg>As and Ni.According to the Standard of Soil Environmental Quality(the second grade value),the contents of the heave metals(As,Hg,Cd and Ni)in pot soils were well complied with the Environment Quality Standard,but the environmental effect of FGD-gypsum improving heavy soda-saline soil still need long-term monitoring.