Simulation Of Water Transport In Different Soil Reconstruction Models Of Dry Iron Tailings

Due to the low grade of iron ore,a large number of tailings are produced during the mining and beneficiation process.Long-term accumulation not only occupies local cultivated land and forest land resources,but also destroys and pollutes the local ecological environment and water quality.It is imperative to reconstruct the tailings matrix,improve the physical properties of tailings and promote ecological restoration because of its fine particles,high density,low nutrient content,poor ventilation and permeability.Thence,this paper took the Quanzigou iron tailings reservoir in Yuanqu County,Shanxi Province as the research area,and observed the water transport process of different reconstructed soils through indoor simulation.The two factors of bulk density and soil mixing ratio were set,and each factor included five levels.A total of 25 treatments of experiments were conducted.The effects of bulk density and soil mixing ratio on the water transport characteristics of iron tailings were analyzed.The main conclusions were as follows:(1)The water holding capacity of reconstructed iron tailings matrix was affected by bulk density.Under the same matrix suction,the water content of iron tailings,soil-mixing 25% and 55% modes decreased as bulk density increased,while the water content of 75% and pure soil modes increased as bulk density increased.The water holding capacity of iron tailings was the best at 1.60 g/cm3,and the water holding capacity of other reconstruction modes was the highest at 1.50 g/cm3.Under the optimal water holding capacity of the five remodeling modes,the pure soil mode had the best water holding capacity,and the water holding capacity was generally enhanced with the increase of the proportion of the soil.(2)The accuracy of van-Genuchten model,Brooks-Corey model and Gardener model in simulating measured water characteristic curve showed that van-Genuchten model R2 was higher than 0.988 and RMSE was less than 0.076,which was the best fitting model for reconstructing soil water characteristic curve from iron tailings.Specific water capacity,field water holding capacity,saturated water holding capacity and maximum water available content gradually decreased with the increase of bulk density.Compaction seriously reduced the amount of macropore,and reduced water use efficiency and water supply capacity of reconstructed iron tailings matrix.(3)With the increase of bulk density,the saturated water conductivity decreased significantly.The power function can better fit the trend of saturated water conductivity with bulk density,R2 is greater than 0.943.Under the same bulk density,the influence of soil-mixing ratio on saturated hydraulic conductivity was as follows: saturated hydraulic conductivity decreased significantly with the increase of soil-mixing ratio.Under 160g/cm3 high compaction,the saturated hydraulic conductivity of 75% soil-mixing ratio was 1.6 and 1.8 times higher than that of 50%,25% soil-mixing ratio,respectively.(4)The infiltration characteristics of reconstructed iron tailings decreased with the increa se of bulk density.Iron tailings,soil mixing ratio 75%,50%,25% and soil from loose to compact the average infiltration rate varied from 0.165 to 0.120cm/min,0.166-0.120cm/min,0.146-0.10cm/min,0.158-0.1cm/min and 0.193-0.103cm/min,respectively.The range of the wetting peak forward distance was: 42.9-50.9cm,45.3-46.7cm,33.6-43.7cm,30-44.8cm and 7.6-65.9cm;The range of cum ulative infiltration is 23.1-29 cm,23-29.4cm,18-27 cm,16-27.7cm and 15.4-44.4cm,respectively.Co mpaction had obvious effect on reducing infiltration,which seriously weakened the infiltration perf ormance of iron tailings matrix.Kostiakov model can accurately simulate the water infiltration proc ess of iron tailings under different reconstruction modes,The average values of R2 and RMSE was 0.97 and 0.045,respectively.(5)Soil mixing ratio had a significant effect on average permeability,steady permeability,advance distance of wetting peak and cumulative infiltration of reconstructed soil.The infiltration performance of the three sand mixing modes with 25% soil mixing rate was the best under the condition of constant bulk density.The difference of wetting peak forward distance and cumulative infiltration between different reconstruction modes on bulk density sensitivity was as follows: bulk density had the most obvious effect on soil remodeling volume accumulation and wetting peak advance distance,and the effect of bulk density on cumulative infiltration and wetting peak forward distance decreased with the decrease of soil mixing ratio in three sand mixing modes.(6)The volumetric water content of iron tailings and soils decreased with the increase of soil depth in the infiltration process.The volumetric water content of iron tailings and soils decreased with the increase of soil bulk density in the depth of 0-20 cm.In the same soil depth,soil water storage capacity was much higher than iron tailings.On the whole,the water storage capacity of three sand mixing modes with constant bulk density was the highest when the soil mixing ratio is 75% at the depth of 0-20 cm soil layer.