| The main characteristics of saline-alkali soil are low content of soil nutrients,less amount of soil aggregates,easy compaction of soil texture,poor water permeability and air permeability,and dispersed soil structure.It has affected the development of agriculture.Iron tailings is a by-product of iron ore processing industry production,with large output and low utilization rate of resources,iron tailings accumulation has become a major challenge for waste disposal in China.However,there are a lot of nutrient elements in iron tailings which can be absorbed by plants.Using iron tailings to make improved materials of saline-alkali soil has the dual effects of environmental protection and ecological reconstruction.So according to the recycling economy and green development concepts,research and utilization of iron tailings were conducted.The mechanical grinding and acidizing method was used to prepare the silicon sustained-release material of iron tailings,and the field test was carried out.The results are as follows:The optimum grinding conditions were as follows:grinding time 120 min,grinding speed 500 r/min,grinding concentration 60%,sodium pyrophosphate as grinding aid,the grinding effect of iron tailings was the best.Then,according to the relationship between sediment particle size and settling rate,water separation is carried out to improve the proportion of small particle iron tailings by grinding iron tailings,and micro-nano iron tailings within the same particle size range are screened out.At this time,the particle size characteristics of micro-nano iron tailings are as follows:D50（14.1μm）,De（8.68μm）,n（0.878）,specific surface area(539.5 m2·kg-1),available silicon content（4835 mg/kg）.The particle size composition is<5.21μm（19.47%）,5.21-21.2μm（79.14%）,>21.2μm（1.39%）.The micro-nano iron tailing powder will be prepared.Different kinds of acid dissolution were carried out to react with iron oxides in iron tailings to optimize particle size distribution.The addition of 0.04mol/L sulfuric acid solution has the best effect on the improvement of iron tailings,which further optimizes the particle size composition of micro and nano iron tailings,improves the proportion of fine particle iron tailings powder,and can obtain long-term accumulation of effective silicon content under natural conditions.At this time,the particle size characteristics of micro-nano iron tailing powder are D50（13.5μm）,De（5.92μm）,n（0.902）,specific surface area(571.8 m2·kg-1)and available silicon content（7366 mg/kg）.Its particle size is less than 5.21μm（27.17%）,5.21-21.2μm（72.02%）,>21.2μm（0.81%）.Pot experiment has verified that the Si-slow release fertilizer of iron tailings acidified by sulfuric acid is beneficial to the improvement of saline-alkali soil.Field experiments were carried out to confirm the effects of silicon slow-release fertilizer from iron tailings on physicochemical properties of saline-alkali soil and rice yield.The slow-release silica fertilizer of iron tailings can obtain long-term effective silica release in the soil,which is better than the soil without iron tailings and untreated iron tailings.The organic matter and alkali-hydrolyzed nitrogen in saline-alkali soil increased with the increase of the content of silicon-release material.The content of available silicon in saline-alkali soil increased and the available phosphorus dissolved continuously.The p H and salt content of saline-alkali soil decreased continuously.The yield of rice per mu has been increasing.When 200 kg/mu was added,organic matter increased to 19.4 g/kg,alkali-hydrolyzed nitrogen increased to 45.38 mg/kg,soil salt content was 2.87 g/kg,soil p H was 8.29,and rice yield was 490.9 kg/mu.Compared with the saline-alkali soil with untreated iron tailings,the rice yield per mu increased by 95.8 kg（24.2%）. |
