Limestone In Hunan Area Study On The Treatment Effect And Mechanism Of Acid Mine Drainage

Acid mine drainage(AMD)has the characteristics of large water volume,low pH and toxic metal ions,which causes serious harm to the ecological environment and human health.Using natural limestone to construct ditch(bed)for AMD treatment can effectively overcome the shortcomings of large amount of lime neutralizing sludge and high operation cost of"alkali+flocculant",which embodies the concept of mine ecological treatment.However,the main problems that affect the application of limestone channel(bed)are channel(bed)plugging and coating on limestone surface.Hunan Province is a big mining Province,and limestone is widely distributed.It has both theoretical value and practical significance to carry out research on AMD treatment of limestone.In this paper,the effects of limestone particle size,initial concentration of metal ions,initial pH and temperature on the removal of metal ions(Fe,Mn,Zn,Pb,Cd)and acidity in AMD by limestone were studied by static test in laboratory.The results show that limestone particle size and initial pH have the greatest impact on the treatment effect.The research results are as follows:(1)When the particle size of limestone is from 0.5cm to 5cm,the treatment effect of limestone on AMD is obviously weakened,and the treatment effect of wastewater with particle size of 0.5cm and 1cm is relatively close,which is obviously better than 3cm and 5cm.It shows that when the particle size is small enough,the effect of changing particle size is not significant.(2)When the initial concentration of metal ions in AMD decreases,the treatment effect of limestone on AMD increases.Five minutes before the test,the removal efficiency of metal ions with high initial concentration and low initial concentration was more than twice,indicating that the higher the metal ion concentration,the more difficult the AMD treatment.In the acid environment with high metal ion concentration,especially high iron concentration,limestone surface is easy to form coating,which hinders the dissolution and alkali release of limestone.(3)When the initial pH of AMD is from 2 to 5,the treatment effect of limestone on AMD is significantly improved.The lower the initial pH is,the worse the adsorption effect of limestone on heavy metal ions is,and the lower the solution pH is,the easier the coating is to be formed,which hinders the continuous dissolution of limestone.(4)When the temperature is from 5? to 30?,the treatment effect of limestone on AMD is slightly improved.The adsorption process of limestone to metal ions is endothermic,and the reaction is spontaneous.High temperature promotes the adsorption behavior of limestone.It also shows that the treatment capacity of limestone ditch in summer is better than that in winter.On the basis of the static test results,the dynamic test of limestone ditch is used to study the influence of water flow speed on sediment settlement,so as to try to solve the problem of limestone ditch plugging and limestone surface coating.The research results are as follows:(1)When the flow velocity is small,the problem of blockage in limestone ditch is serious.When the flow velocity reaches 0.0215m/s,the flow can smoothly remove the sediment generated in the water and effectively solve the problem of blockage in limestone ditch.(2)When the flow rate reaches 0.2785m/s,the sediment in the limestone ditch is suspended,which greatly promotes the surface erosion of limestone,and the coating problem on the surface of limestone is greatly improved,which is the key to the long-term treatment capacity of limestone ditch.(3)When the flow rate reaches 0.2785m/s,limestone ditch can remove metal ions except Mn,and the removal rates of Fe,Zn,Pb,and Cd are 70.54%,70.60%,96.50%and 56.20%respectively after 60min,and 99.25%,97.55%,96.50%and 97.85%respectively after 120min,which are up to the emission standard.However,the removal efficiency of Mn is not good.The removal rate is only 16.80%at 60min and 43.50%at 120min,which does not meet the emission standard.It is suggested to add other measures,such as increasing the hydraulic retention time,increasing the system pH.