Research On The Optimization Of Phosphorus-based Passivation Repair Material

Lead-zinc tailings are solid waste containing a large amount of heavy metals,typically including Pb,Zn,Cu,Cd,etc.The heavy metals in tailings are prone to migration into the surrounding environment,posing risks to groundwater,soil,and plants in the surrounding environment.Therefore,it is very necessary to passivate and repair the heavy metals in lead-zinc tailings.A large number of previous studies have shown that phosphorus based materials such as hydroxyapatite,phosphate rock powder and phosphate fertilizer have good passivation ability for Pb,Zn,Cu and Cd.This study selected phosphorus ore powder and yellow phosphorus slag from phosphorus mines and phosphorus chemical enterprises as phosphorus based materials to passivate and cultivate heavy metals in lead-zinc tailings.At the same time,the phosphorus based materials were modified and compounded to find ideal modified and compounded materials for repairing heavy metals in lead-zinc tailings.Through experimental research,the following conclusions have been drawn:(1)Characteristics of lead-zinc tailings: According to the new version of soil environmental quality standards,Cd and As in lead-zinc tailings exceed the standard,resulting in a high risk of pollution;The relative risk screening values of Pb and Zn exceed the limit,but the content index is only used as a reference for pollution risk.A more direct risk assessment should use the toxicity characteristics of heavy metal leaching.(2)The leaching experiments on the toxicity of heavy metals in lead-zinc tailings were conducted using the sulfuric acid nitric acid method and the TCLP method,indicating that the sulfuric acid nitric acid method is not suitable as a risk assessment method,and the TCLP method is more objective in assessing the toxicity risk of heavy metals.(3)The leaching of heavy metals Pb,Zn,and Cd from tailings,such as lead and zinc,is influenced by p H,and both Pb and Zn exhibit the characteristics of amphoteric elements,while Cd exhibits the characteristics of alkaline elements.The leaching concentration of Pb rapidly increases in the environment with p H<1.5 and>12;The leaching concentration of Zn increases significantly at p H<2.5 and>12;Cd only increases in leaching concentration when p H<2.5.(4)In terms of passivation of heavy metals in lead-zinc tailings using phosphorus based materials,the passivation efficiency of yellow phosphorus slag on Pb and Cd in lead-zinc tailings is higher than that of phosphate rock powder.The particle size of yellow phosphorus slag has no significant impact on the passivation effect,and increasing the amount of yellow phosphorus slag added will improve the passivation effect.The passivation effect of yellow phosphorus slag and phosphate rock powder on Zn is not ideal.(5)Ferrous sulfate modified yellow phosphorus slag enhances the passivation efficiency of Cd,Pb,and Zn,while ferrous sulfate modified phosphate rock powder significantly improves the passivation efficiency of Pb and Zn,with limited effect on Cd.Oxalic acid and ammonium oxalate have poor effects on modified yellow phosphorus slag,and they are not suitable as modified materials for yellow phosphorus slag.(6)In the composite materials,the combination of polymerized iron sulfate and yellow phosphorus slag can enhance the passivation efficiency of Pb and Zn,and significantly improve the passivation efficiency of Zn;The combination of calcium carbonate and yellow phosphorus slag can effectively increase the passivation efficiency of Cd and Zn,with the most prominent improvement on Zn,but the passivation efficiency of Pb is reduced;The combination of potassium dihydrogen phosphate and yellow phosphorus slag can effectively increase the passivation efficiency of Pb and Cd,with the most prominent effect on Pb,but it will cause the activation of Zn.Overall,the passivation effect of polymerized iron sulfate combined with yellow phosphorus slag on lead-zinc tailings is the most ideal.