Study On The Effect Of Pine Needle Biomass Smoldering On Tailings Soiling

Due to extensive production methods and backward management techniques,a large number of tailings have generated many hazards during the stockpiling process,such as causing geological disasters,polluting surrounding soil,air,and groundwater.In addition,tailings occupy land resources and cause resource waste.Tailings are highly degraded in physical and chemical properties,characterized by scarced nutrients,high heavy metal content,loose structure,and poor water retention,which are not conducive to plant growth.One of the important measures to achieve the maximum resource utilization of tailings is to improve tailings into a soil like matrix(i.e.,to soil tailings),with the aim of restoring their biogeochemical capabilities and developing soil functions.By fixing heavy metals,improving tailings matrix,creating soil structure,enhancing soil nutrients and promoting plant growth,ecological restoration of the mining area can be achieved.In this study,three different types of tailings,including copper tailings,tin tailings,and tin oxide tailings were used as research objects.Pine needle biomass(PN)was used as supplemental fuel to investigate the effects of smoldering on the physical and chemical properties,available forms of heavy metals,chemical forms of heavy metals,and weathering of tailings minerals through smoldering heat treatment.The effects of smoldering treatment on the soiling of tailings were investigated through the retention of nutrients in tailings and the growth of potted experimental plants in an alternate dry and wet experiment.The main conclusions are as follows:(1)The self sustaining smoldering of the mixture of tailings and PN was realized in a self-made smoldering device.The smoldering characteristics significantly change with the mass ratio of tailings to PN.As the PN ratio increases,the average smoldering peak temperature increases,and the smoldering propagation speed increases.This indicates that in practical engineering applications,the soil utilization efficiency of tailings can be controlled by changing the biomass ratio.(2)Compared with the control group,smoldering treatment significantly increased the p H,electrical conductivity(EC),organic matter,and available nutrient content of the tailings(P<0.05).However,there are differences in the fixation effects of smoldering treatment on different heavy metals in tailings.It has a strong passivation effect on Cu,Zn,Pb of copper tailings and Cu,Zn,Mn of oxide tin tailings,significantly reducing the DTPA extraction available content.On the contrary,smoldering treatment promoted the effective release of Cu,Zn,Mn,and Pb from tin tailings.The distribution of the occurrence forms of heavy metals in the three tailings is as follows: residual>acid soluble>reducible >oxidizable.The acid soluble content of heavy metals Cu and Zn of copper tailings gradually decreases with the increase of PN ratio in smoldering treatment.In tin tailings,smoldering treatment significantly increases the content of acid soluble,reducible,and oxidizable states of Cu,Zn,Mn,and Pb,which is the reason for the increase in effective states.However,on the whole,the residual state is the main existing form and does not pose a significant risk to the environment.(3)XRD and SEM characterization indicate that smoldering treatment accelerates the weathering and transformation of tailings minerals,and promotes the transformation of primary minerals into secondary minerals.After smoldering treatment of copper tailings,primary minerals such as plagioclase and biotite disappear,and are transformed and weathered into clay minerals such as vermiculite and kaolinite.Under smoldering high temperature conditions,the secondary minerals aragonite,hematite,and iron calcium oxide in tin tailings increase,indicating that primary minerals are transformed into secondary minerals.In SEM morphology characterization,minerals with large particles on the surface of minerals broken into small particles and irregular shapes also confirmed that minerals undergo weathering.(4)In the drying-rewetting culture experiment,the organic matter,available phosphorus,and available potassium nutrient contents in the smoldering treatment group were higher compare with the control group,and the decrease trend was slow with the increase of incubation time,indicating that smoldering treatment can effectively inhibit nutrient absorption in tailings.At the same time,the available states of heavy metals Cu,Zn,Mn,and Pb in the three tailings increased first and then decreased with the increase of incubation time,reaching a peak at 34 days.(5)In the pot experiment,compared to the control group,smoldering treatment significantly promoted the growth of the stems and roots of ryegrass,with a more significant impact on the roots of ryegrass than on the stems(P<0.05);The smoldering treatment significantly inhibited the absorption and enrichment of heavy metals Cu,Pb in copper tailings,Zn in tin tailings,and Cu,Zn,and Pb in tin oxide tailings by the stems and roots of ryegrass,but promoted the enrichment of Mn in the three types of tailings by ryegrass.Overall,the concentration level of heavy metals in the roots of ryegrass was significantly higher than that in the aboveground parts.Analysis of the tailings matrix after plant colonization found that the combination of smoldering treatment and plant colonization neutralized the p H of the tailings matrix;Significantly increased the contents of macroaggregates,EC,organic matter,available phosphorus,available potassium,and available nitrogen in the tailings matrix(P<0.05);The activities of urease and phosphatase in the tailings matrix were significantly increased(P<0.05),which was beneficial to the soil utilization of tailings.