Environmental Risks And Soil Improvement Of Stainless Steel Slag

As a byproduct of iron and steel metallurgy industry, steel slag is an industrial solid waste having large emissions. Steel slag stores as waste, not only occupy the farmland, but also cause a lot of pressure to the local environmental governance. Social policies, such as circular economy, ask the iron and steel enterprises to realize the comprehensive utilization of steel slag. Stainless steel slag is rich in Ca, Mg, Si, and other elements and has been used for soil improvement and as a fertilizer in agriculture. Stainless steel slag is also potentially useful for remediation of heavy metal pollution due to its porosity, large surface area, and good adsorptivity. But stainless steel slag also contains little amount of heavy metals. Therefore, it is necessary to study the potential environmental risk of stainless steel slag before it is used in agriculture. In this regard, domestic and foreign scholars rarely study.This thesis aims to study the effect of stainless steel slag on heavy metal accumulation in soil-crop system, and conduct environmental safety assessment. At the same time, a preliminary study was carried out to explore the feasibility of stainless steel slag used for soil improvement by studying the remediation of heavy metal polluted soil using stainless steel slag.Now the main results of this study are summarized as follows:1. The application of stainless steel slag has no significant impact on fresh weight of rape, but when the application rate of stainless steel slag reached to certain content, it can reduce rape height, increase the MDA content of rape, and inhibit the root activity of rape. The adjunction of weathered coal can increase the height and fresh weight of rape, reduce the MDA content and improve the resistance of the rape, but can not significantly improve the root activity of rape.2. The application of stainless steel slag have no significant impact on Zn, Pb content, but can increase Cr, Ni content, reduce Cu, Cd content. The adjunction of weathered coal can reduce soil Pb, Cd content. Soil environmental quality evaluation results show that the application of stainless steel slag has little influence on heavy metals, the contents of heavy metals are within the safe range, the application of stainless steel slag will not pose security risk to soil environment.3. The application of stainless steel slag can increase soil pH, soil cation exchange capacity and available P content, but have no significant impact on soil organic matter and soil total nitrogen, but reduce available K content. The adjunction of weathered coal can increase soil organic matter, soil total nitrogen and available K content.4. The migration and accumulation of heavy metals in rape show that accumulation of Cr, Cu, Zn in the shoot of rape is greater than in the underground, but accumulation of Cd, Ni show the opposite. The application of stainless steel slag can increase heavy metal content of rape, while the adjunction of weathered coal can inhibit the accumulation and migration of heavy metals to plants. Safety assessment shows that heavy metal contents of rape are in the safe range.5. Application of organic fertilizer, co-application of organic fertilizer and stainless steel slag could significantly increase the grain weight of corn. Heavy metal elements accumulate more in maize roots, leaves and stems, less in spike and grain. Compared with the control, in organic fertilizer processing, heavy metals in various organs of corn do not change significantly, while in two processings of co-application of organic fertilizer and stainless steel slag, some heavy metals have increased in maize roots, leaves and stems. Safety assessment shows that heavy metal contents of corn are in the safe range.6. Compared with the control, soil pH and cation exchange capacity of each test area have no significant change, but available phosphorus increase significantly. Organic matter, total nitrogen, and available potassium in soil surface significantly increase compared with the control. Compared with the control, soil heavy metals of test areas are not significantly change. Soil environmental quality evaluation results show that the application of stainless steel slag has little influence on heavy metals, which are within the safe range, will not pose security risk to the soil environment. 7. The co-application of ammonium humate and stainless steel slag significantly decreased the total and available soil cadmium concentrations. The application of stainless steel slag can increase soil pH, decrease soil aggregates, but have no significant impact on soil organic matter and cation exchange capacity. Co-application of ammonium humate and stainless steel slag can significantly increase soil organic matter, cation exchange capacity and soil aggregates.To sum up:1. The application of stainless steel slag can cause the increase to soil heavy metals, but which do not exceed the limit contents of Soil Pollution Technical Tequirements. Soil environmental quality evaluation results show that the application of stainless steel slag has little influence on heavy metals, the contents of heavy metals are within the safe range, the application of stainless steel slag will not pose security risk to soil environment. The application of stainless steel slag can increase heavy metal content in oilseed rape and maize plants, but which do not exceed the limit contents of Agricultural Products Evaluation Criteria. Eatting oil vegetables and corn will not bring hazard to human health.2. When the application rate of stainless steel slag reached to certain amount, it can reduce rape height, increase the MDA content of rape, inhibit the root activity of rape, and cause some damage to rape plants, and stainless steel slag can bring a increase in pH value to soil. Thence when stainless steel slag is applied to farmland, the application rate must be controlled.3. The co-application of ammonium humate and stainless steel slag can be used for the remediation of heavy metal contaminated soil and improvement of soil properties.