| At present,the problem of soil pollution in my country is becoming more and more serious.In order to improve soil quality,pollution such as soil needs to be treated.Shell powder,as a small particle size and alkaline material,can be used as an adsorption material for the treatment of heavy metal pollutants.In this paper,the adsorption capacity and adsorption mechanism of shell powder on heavy metal ions were studied,and the effects of seepage velocity,heavy metal types,shell powder addition amount/concentration and other factors on the adsorption effect of shell powder in the treatment of heavy metal pollutants in laterite and quartz sand were analyzed.The adsorption mechanism of cadmium and lead by shell powder was analyzed by means of adsorption kinetics test,adsorption-desorption test,scanning electron microscope and Fourier transform infrared spectroscopy test.The effect of shell powder on the adsorption effect was studied by static adsorption test and dynamic adsorption test.The conclusions are as follows:(1)By analyzing the adsorption mechanism of shell powder,it is found that the adsorption of shell powder is divided into three stages: one is the surface adsorption stage,which mainly depends on the fastest adsorption rate of physical adsorption;the second is the diffusion stage in the pores,which is the stage of physical adsorption.It coexists with chemical adsorption,and the chemical adsorption that occurs when cadmium is adsorbed is found to be stronger through testing and analysis;the third is the equilibrium stage,in which the adsorption amount does not change significantly,and the adsorption is in dynamic equilibrium.The adsorption-desorption test results show that the nonlinear adsorption-desorption model is the most accurate in describing the adsorption-desorption process of shell powder,and the model takes into account the residual adsorption capacity.The utilization of shell powder will be higher in high concentration environment.(2)Through the static adsorption test,the following conclusions were obtained:the dissolution amount of ions in heavy metal contaminated soil is very limited in a neutral environment,and the addition of shell powder has little effect on the test results in a neutral environment,and the standing time is the main factor affecting the adsorption effect;In the acid leaching test,after replacing the laterite with a certain amount of shell powder,the leaching amount of cadmium and lead decreased,which proved that shell powder showed stronger adsorption for these two heavy metals in the competitive adsorption between shell powder and laterite.ability;Adding a certain amount of shell powder is necessary for the treatment of cadmium-contaminated soil.In lead-contaminated soil,as long as the standing time is sufficient,the leaching concentration of shell powder can reach the national standard regardless of whether the shell powder is added.It only plays an optimization role when polluting the soil;In an acidic environment,there are more free heavy metals,so the harm to the surrounding environment of the soil is higher,and the shell powder has a greater impact on the concentration of the leaching solution in the toxicity leaching test.Therefore,the shell powder can play a role in the treatment of heavy metal pollution in the soil in an acidic environment.effect will be greater.(3)Through the dynamic adsorption test,the conclusions are as follows: the seepage velocity will increase the concentration of heavy metal ions in the effluent,and at the same time reduce the residual concentration in each section of the sand column;There are certain differences between cadmium and lead in the process of dynamic adsorption.The concentration of lead ions in the effluent is slightly lower than that of cadmium,and the residual concentration of lead at the cross-section is higher than that of cadmium.The residual concentration of lead at the cross-section after being washed by the shell powder solution is lower than that of cadmium,which is due to the better adsorption effect of shell powder on lead.Combined with this phenomenon,the shell powder will have a better effect on the treatment of lead-contaminated coarse-grained soil;The concentration of the shell powder solution is the most critical factor affecting the adsorption effect.When the concentration of the shell powder solution is increased,the concentration of heavy metal ions in the effluent will decrease,and the residual concentration of heavy metals at the cross section of the sand column will also decrease.In addition,increasing the concentration of the shell powder solution will also reduce the difference caused by the seepage velocity and different types of heavy metals,so the concentration of the shell powder solution is the key to controlling the adsorption effect in the dynamic adsorption process. |
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