Ni²⁺ Was Removed From Water By Carrier-induced NiS Precipitation Crystallization

Nickel is a non-ferrous heavy metal and belongs to the first category of pollutants.It is widely used in various industries because of its good properties.At present,among the methods used to remove Ni²⁺from wastewater,chemical precipitation method is widely used,but its process is cumbersome and the removal speed is slow;Carrier induced precipitation crystallization method is an improved technology of traditional chemical precipitation method.It has the advantages of small amount of precipitant,high removal rate and simple process.It can be used to remove all kinds of precipitable ions.The research on the removal of Ni²⁺from wastewater by carrier induced Ni S precipitation and crystallization can provide a theoretical basis for future engineering practice.Taking Ni²⁺water as the treatment object,Na₂S as the precipitant,10 kinds of natural minerals as the induction carrier and dimethylglyoxime spectrophotometry as the measurement means,the following studies are carried out:（1）The effects of different pretreatment conditions on the determination of Ni²⁺with and without carrier were investigated,and the best pretreatment conditions were obtained;Under the optimal precipitation conditions without carrier,the induction effects of each carrier,including removal efficiency and equilibrium time,were compared to select the optimal carrier;Determine the main mineral composition of each carrier and analyze the qualitative relationship between it and removal rate,so as to provide a preliminary direction for carrier selection and preparation.（2）Carry out the research on simple carrier selection methods,including the correlation between zeta potential and precipitation equilibrium system in the process of induced precipitation crystallization,Ni²⁺containing water distribution system,deionized water system and Ni²⁺removal effect,and verify the method obtained by the research group in the early stage,especially the universality of using isoelectric point to select carrier.（3）Carry out experiments on the best induction conditions of the best carrier in different regions to obtain the carrier with the best induction effect;Using the carrier composition analysis results obtained by the research group in the early stage,carry out the correlation analysis between the removal efficiency and the components,quantify the correlation between the induction effect and the carrier composition,and provide the composition basis for the preparation of the carrier in the future;The kinetic model and activation energy of the reaction without carrier and the best carrier are compared,and the changes of the reaction process with and without carrier are analyzed from the perspective of kinetics,so as to provide a basis for the subsequent preliminary discussion of the induction mechanism.（4）Carry out the best carrier surface dissolution and adsorption test,and analyze whether the decrease of Ni²⁺concentration is caused by precipitation reaction or carrier adsorption in the process of Ni S precipitation and crystallization;Carry out SEM,XPS and XRD characterization before and after crystal induction of the best carrier,and analyze whether the precipitation reaction occurs on the surface of the carrier;Combined with zeta potential data,electric double layer theory and kinetic conclusion,the reaction process of removing Ni²⁺by Ni S precipitation crystallization induced by the best carrier is preliminarily analyzed.The results show that:（1）the order of induced removal rates of different carriers from large to small is as follows:Hebei dolomite>fluorite>calcite>refined quartz sand>garnet>feldspar>Natural Quartz Sand>analytical quartz sand;The order of reaction reaching equilibrium time from small to large is:Hebei dolomite=fluorite=15 min2exist in the natural mineral components of induced precipitation crystallization effect is better,It is consistent with the research results of carrier induced precipitation to remove Pb²⁺and PO₄^3-carried out by the research group in the early stage and the same period,which preliminarily indicates that attention should be paid to its mineral composition in the selection of carrier.（2）The smaller the absolute value of carrier zeta potential,the higher the removal rate.Its law is similar to the previous research of the research group.The selection method of zeta potential as the best carrier in the precipitation process is universal.Zeta potential can be used to regulate the p H value,precipitant dosage ratio and carrier dosage in the precipitation crystallization process,so as to reduce the workload of process control,adapt to the changes of water quality and maintain the removal rate at a high level.In the precipitation equilibrium system,Ni²⁺containing water distribution system and deionized water system,the effect of removing Ni²⁺induced by 10 carriers is related to the isoelectric point.The larger the isoelectric point of the carrier,the better the effect of removing Ni²⁺,and the carrier can be selected by isoelectric point.The results are consistent with the conclusions obtained by the research group in the early stage and the same period.The method of using isoelectric point to select the carrier is universal for cations and anions.The methods are relatively simple and easy.Among them,the determination of isoelectric point of carrier in deionized water system is the simplest,which can be used as the best method of carrier selection.（3）Under the optimum conditions,the effect of inducing NIS precipitation and crystallization is different for dolomites in different regions,and the effect of inducing Ni2+removal by dolomite in Hebei is the best.The sensitivity of dolomite composition positively correlated with Ni²⁺equilibrium removal rate is as follows:Ca O,Mg O,Si O₂and Al₂O₃,in which Ca O,Mg O and Si O₂are strongly linear positive correlation;The sensitivity of dolomite components negatively correlated with Ni²⁺equilibrium removal rate is as follows:Na₂O,Fe₂O₃,K₂O,Pb²⁺,PO₄^3-equilibrium removal rate shows the same correlation with carrier components,but the sensitivity of each component is slightly different.The results can be used to guide carrier selection and preparation.Both carrier free and dolomite induced NIS precipitation reactions are suitable to be described by quasi second-order kinetic model;Compared with no carrier,the reaction activation energy decreased significantly after adding the carrier;The activation energy of dolomite varies greatly in different regions,which should be related to its composition.（4）The dissolution process of Ca²⁺and Mg²⁺on the surface of dolomite in Ni²⁺containing water distribution system,precipitation system and deionized water system conforms to the quasi second-order kinetic model,and the dissolution amount decreases in turn;The adsorption capacity of dolomite for Ni²⁺is small.The decrease of Ni²⁺concentration in dolomite induced Ni S precipitation crystallization is mainly caused by precipitation reaction,which occurs on the surface of the carrier;During the precipitation and crystallization of Ni S induced by dolomite,the surface charged forms are Ca O^-,Mg O^-,and the precipitant S^2-reacts with Ni²⁺in the double-layer counter ion adsorption layer.Compared with the case without carrier,the reaction process changes,and the removal rate and reaction rate increase.