Study On Physical And Chemical Reconstruction Technology Of Coal Mine Temporary Construction Land In Chongqing

Coal mining will lead to many ecological environment problems.The industrial square,ancillary buildings and coal gangue above the temporary construction land of coal mine will cause the destruction of the natural landscape and soil structure destruction and the waste of land resources.The increasingly serious destruction of soil physical and chemical properties of coal mine temporary construction land is an urgent problem for us to solve.The mine reclamation in our country started late,and there are few regulations about the soil restoration of coal mine temporary construction land.In our country,Most of the current technology of land reclamation in coal mining area is engineering reclamation technology,and coal gangue is usually used as filling matrix.On the one hand,using coal gangue as filling matrix will repair the coal mining subsidence and micro topography changes,on the other hand,reconstruction of agricultural soil,such a reduction in the process of,on the other hand,using coal gangue as filling matrix will also reduces the ratio of coal gangue accumulation area and the degree of the secondary pollution to the external environment.However,there is still a lack of research on the characteristics of soil water and nutrient movement in reconstructed soil filling with coal gangue,so this paper chooses three Chongqing local soil（purple soil,yellow cold sand soil,yellow soil）to combine with coal gangue to reconstruct soil and sets up ten groups of soil reconstruction treatments.These treatments include four kinds of soil reconstruction treatments filling individually with coal gangue,purple soil,yellow soil and yellow cold sand soil（A,B,C,D）;they also include three kinds of soil reconstruction treatments mixed filling with coal gangue respectively with purple soil,yellow cold sand and yellow soil（AB,AC,AD）;they also include three kinds of soil reconstruction treatments layered filling with coal gangue respectively with purple soil,yellow cold sand and yellow soil（AB1,AC1,AD1）.Through the water wetting front,cumulative infiltration,the characteristics of nitrogen,phosphorus and other nutrients in infiltration experiment and leaching experiment,this paper analyze the ability of water retention and fertilizer retention in different reconstructed soil types.At the same time,it also reveal the effect of different reconstructed soil types on plant growth through the plant growth test.These analyses will provide theoretical basis for the coal mine temporary construction land reclamation in Chongqing.The main research contents and results are as follows:（1）With the increase of the bulk density of coal gangue,the saturated volumetric water content increases.The density of coal gangue under 1.50 and 1.60 g/cm³ have higher saturated volumetric water content,which is respectively of 37% and 34.8%.But the saturated mass water content are lower,which is only about 23.9% and 22.7%.The saturated volumetric water content and saturated mass water content under 1.40 g/cm³ are 33.6% and 24.3%.The water holding capacity and water infiltration rate under 1.40 g/cm³ are moderate,and they are conducive to the reconstruction of the soil to retain water..Therefore,we choose 1.40 g/cm³ as the coal gangue density to take soil reconstruction experiment in this study.（2）There are some differences in the characteristics of water movement in different reconstructed soil types.The running rate of wetting front in mixed and layered filling reconstruction soil treatments are significantly less than that of single coal gangue filled reconstruction soil treatment,so the mixed and layered filling reconstruction soil treatments are conducive to maintaining soil water.The advancing rate of wetting front in mixed filling reconstruction soil is slower than in the layered filling reconstruction soil,and at the later stage of infiltration experiment,the rate of layered filling reconstruction soil was decreased,so the layered filling reconstruction soil have a greater obstacle to the water infiltration in coal gangue,and they have a stronger effect to slow down soil moisture loss than the mixed filling reconstruction soil.In the water infiltration test,the cumulative infiltration in layered and mixed filling reconstruction soil is AB: 63 cm,AC: 57 cm,AD: 68 cm,AB1: 68 cm,AC1: 61 cm,AD1: 78 cm,so the cumulative infiltration in layered filling reconstruction soil is more than in mixed filling reconstruction soil.The results show that the layered filled reconstruction soil is more conducive to the absorption and retention of water than the mixed filled reconstruction soil.（3）The effects of different reconstruction soil types on the ability of fertilizer retention are different.In the nutrient leaching experiment,the leachingconcentration of NH4+-N in layered filling reconstruction soil is significantly less than in single coal gangue filling reconstruction soil.Compared to single coal gangue filling reconstruction soil,the leaching concentration of NH4+-N in mixed filling reconstruction soil is grow rather than decrease,and the possible reason is that the soil structure of coal gangue is poor,the porosity is large,and the NH4+-N is more easier to be converted to NO₃^--N.The leaching concentration of NO₃^--N and TN in AB,AD,AC1 and AD1 is relatively less than other treatments.Compared with A treatment,the leaching concentration of NO₃^--N and TN in AB1 are respectively increased by 5.84 and 10.15 mg/L;AD has the lowest NO₃^--N leaching concentration,which is only 12.58 mg/L.the leaching concentration of NO₃^--N in AC1,AD1,AB are 18.11,18.31,18.84 mg/L.AD1 has the lowest leaching concentration of TN,which is only 20.53 mg/L,followed by AD（23.07 mg/L）and AC1（26.44 mg/L）.There are little leaching loss of TP and PO43-in all different reconstruction soil,and there are no significant differences between the different reconstructed soil.There have significant correlations between the pH value and all chemical properties（P<0.01）.Therefore,the leaching loss of NH4+-N in AB1,AC1 and AD1 are less than othertreatments,while the leaching loss of NO₃^--N and TN in AD,AC1,AD1 and AB are less than other treatment.（4）the effects of each reconstructed soil on crop growth are also different.In the process of crop growth,the order of the soil surface water content in mixed filling and layered filling reconstruction soil is: AB1（21.15%）> AB（20.70%）>AD1（20.58%）>AD（20.15%）>AC（18.24%）>AC1（12.24%）,so the soil surface water content in AB1,AB and AD1 are relative larger than other treatments,and the soil surface water content in AC1 is the minimum one.At harvest time,except the surface water content of AC is higher than AC1,the fresh weight,dry weight and water content in AB1,AC1 and AD1 are higher than in AB,AC and AD.Compared with A,the content of TN in mixed filling and layered filling reconstruction soil are higher than 4.41⁵.87,13.25¹7.66 g/kg;the content of TP are higher than 0.01⁰.02,1.26¹.46 g/kg;the content of TK are increased by 0.82⁴.34,10.90¹3.02 g/kg.Compared with A,the content of TN uptake in mixed filling and layered filling reconstruction soil are higher than 7.97¹6.10,87.01¹49.81 mg/strain;the content of TP uptake are higher than 0.02⁰.06,4.59⁸.36 mg/strain;the content of TK uptake are higher than 2.72¹2.63,67.36¹31.64 mg/strain.The amount of lettuce nutrient content and nutrient accumulation in layered filling reconstruction soil are far more than in mixed filling reconstruction soil,so layered filling reconstruction soil is more conducive to the absorption of the nutrient content than mixed filling reconstruction soil.Through the water movement experiment,nutrient loss experiment and letthce growth experiment,it shows that the layered filling reconstruction soil have stronger ability to hold soil water,conserve nutrient,and they also have greater suitability for plant growth.The reconstruction soil treatment layered filling with coal gangue and yellow soil has the best results among all reconstruction soil treatments,so it can be applied to the reclamation of coal mine temporary construction land.