Effect of soil structure conditioner PAM on physical properties of iron tailings in reclaiming

Abstract: Polyacrylamide (PAM) is a common soil structure conditioner, but it is seldom applied in the reclaiming of iron tailings. In order to study the improvement effect of PAM on dry iron tailings, and promote the vegetation restoration on soilless mining area, PAM was added to iron tailings to form 4 mass contents of 0% (control), 0.05%, 0.10% and 0.20% respectively using dry mixing method. The physical properties of mixture were observed and measured by simulating water transporting in soil columns with 10 cm diameter. The results showed: 1) The physical properties of iron tailings added with PAM had some improvement compared to the control, and in the order of PAM mass contents of 0.05%, 0.10% and 0.20%, the bulk density decreased by 1.82%, 3.03% and 4.85%, the total porosity increased by 2.75%, 4.50% and 7.25%, and the capillary porosity increased by 13.39%, 25.03% and 27.54%, respectively. There was significant difference (P<0.05) between the control and the tailings added with PAM. 2) As capillary water rose from 0 to 40 cm in the soil column, the volumetric water content of iron tailings under 4 PAM concentrations all tended to decline. The higher the PAM mass content of iron tailings, the slower the declining trend of volumetric water content with rising height, but the variation coefficient of tailings volumetric water content under 4 PAM mass contents got bigger and bigger from 1.22% to 7.13% with the height rising from 10 to 40 cm. 3) The rising heights of capillary water under 4 PAM mass contents were 25, 14.3, 14.5, and 14.4 cm respectively after the test lasted for 420 min, among which the difference was extremely significant (P<0.01). But in the rising process, the inhibition ability of different PAM mass contents on capillary water was changeable, so the rising process was divided into 3 stages: Stage 1 (0-5 min), similar rising height for different PAM mass contents; Stage 2 (6-25 min), the rising height under 4 PAM mass contents showed obvious difference in the same rising time; Stage 3 (30-420 min), relative stable change of rising height for different PAM mass content. In the whole rising process of capillary water, the rising rate of the control was significantly higher than that added with PAM, but the difference of rising rate under 3 PAM mass contents was not significant. The accumulative rising height of capillary water increased with the time following the power function; the rising rate of capillary water decreased with the time following the power function. 4) In the condition of natural ventilation, the water content of iron tailing under different PAM mass contents reduced continuously, but the extent of reduction was different; the water content change of the control was the sharpest, from 37.53% to 35.60%, and the water content change for 0.20% PAM was minimum, from 37.40% to 36.67%. Therefore, PAM can improve the physical properties of iron tailings, inhibit water loss and create appropriate growth environment for vegetation restoration. The reasonable use of PAM is very beneficial to soilless ecological rehabilitation and erosion control.