The Study Of The Effect And Mechanism Of EDTA On The Formation Of Different Forms Scale Based On Nucleation Kinetics Theory

In the process of water recycling,due to the continuous evaporation of water,the electrolyte dissolved in the water is concentrated,resulting in the precipitation of inorganic substances such as calcium carbonate,calcium silicate,and silica,which adhere to the inner wall of the equipment to form scale.The formation of scale not only block the pipeline,reduce the heat exchange efficiency of the equipment,but also corrode the equipment,causing huge economic losses.In this study,a simple organic compound with multiple carboxyl groups,editic acid(EDTA) is selected as the representative scale inhibitor to study its influence on the formation process of different forms of scale,explore its effect on different scales,and provide scientific basis for the synthesis of high efficiency scale inhibitors and the improvement of scale inhibition efficiency.It provides reference value for preventing the formation of mixed scale in the actual water utilization system.This article takes calcium carbonate,calcium silicate and the mixed system of the two as the research object.By measuring a series of indicators such as solution turbidity,pH and particle size,combined with X-ray diffraction(XRD)and Scanning Electronic Microscopy(SEM) analyze the scale inhibition or promotion of different forms of scale by EDTA,and finally combine the nucleation kinetic theory to reveal the formation mechanism of EDTA on different kinds of scales at the molecular level.The main conclusions are as follows:(1)In the single calcium carbonate system,the addition of EDTA increased the induction time to inhibit the formation of calcium carbonate precipitation.The results of XRD and SEM analysis of crystal form and morphology show that EDTA promotes vaterite to become irregular calcite.The calculation results of nucleation kinetic parameters show that EDTA increases the interface energyγ,the critical free energy change?G_c and the critical nucleation radius r_c,reduces the nucleation rate J,inhibits the nucleation of calcium carbonate,and reduces the amount of crystal nuclei of calcium carbonate in the solution,inhibiting the precipitation of calcium carbonate.(2)In the single calcium silicate system,the addition of EDTA reduced the induction time of calcium silicate,and the induction time decreased with the increase of EDTA concentration,indicating that EDTA promoted calcium silicate precipitation.The results of analyzing the crystal form and morphology of the precipitate by XRD and SEM show that EDTA can promote the polymerization of silica in the system.The influence of EDTA on nucleation kinetic parameters is related to the supersaturation of the system.When the supersaturation index>9.75,EDTA reduces the interface energyγ,the critical free energy change?G_c and the critical nucleation radius r_c,and increases the nucleation rate J to promote calcium silicate nucleation;and when the supersaturation index<9.75,EDTA Increase the interface energyγ,the critical free energy change?G_c and the critical nucleation radius r_c,and reduce the nucleation rate J to inhibit calcium silicate nucleation.(3)In the mixed system(containing 200 mg/L silicic acid),mixed precipitates of calcium carbonate,calcium silicate and silica are simultaneously generated.Adding EDTA has an inhibitory effect on the generation of turbidity,but the inhibitory effect is weakened due to the presence of silicic acid.EDTA promotes the conversion of vaterite to calcite,and also promotes the polymerization and growth of silica,but hinders the mutual aggregation of the overall large particles.The calculation results of nucleation kinetic parameters show that the addition of EDTA reduces the interfacial energyγ,critical nucleation radius r_c and critical free energy change?G_cof the mixed system,increases the nucleation rate J,and promotes the formation of mixed nuclei in the solution.Therefore,EDTA has a dual effect on the formation of mixed scale.It has an inhibitory effect when the concentration of silicic acid is low,and it has a promoting effect when the concentration of silicic acid is high.EDTA is suitable as a scale inhibitor in low concentration silicic acid water.In summary,EDTA has different effects on the formation of different forms of scale.It mainly inhibits calcium carbonate,while the effect on the formation of silicic acid series is related to the concentration of silicic acid,so EDTA has a double effect on the formation of mixed scale.The effect is inhibition when the concentration of silicic acid is low,and promotion when the concentration of silicic acid is high.