Effect Of Circulating Water Scale Inhibitors On The Crystallization Characteristics Of Gypsum

Under the background of zero discharge of wastewater of the whole plant,the desulfurization system undertakes a large amount of low-quality wastewater in the cascade utilization of wastewater,which introduces a large amount of impurities into the desulfurization system.Magnesium ions enter the desulfurization system with limestone slurry and scale inhibitor with circulating cooling water sewage,hindering the normal crystallization of gypsum,thus affecting the quality of gypsum,and failing to realize the high value utilization of solid waste resources,resulting in carbon emissions and environmental pollution.In this paper,gypsum crystallization experiments are carried out according to the conditions of calcium-sulfur ratio,magnesium ion and different scale inhibitors,simulating the gypsum crystallization process,and using metallographic microscopy,scanning electron microscopy,laser particle size analyzer and other equipment to explore its influence on the crystallization characteristics of gypsum.The effect of calcium to sulfur ratio and magnesium ion crystallization on the crystallization characteristics of gypsum is studied.The change of calcium to sulfur ratio and magnesium ion both decrease the gypsum supersaturation ratio and increase the crystallization induction time of gypsum.Magnesium ions affect the structure of gypsum crystals.The gypsum crystal gradually changes from long needle shape and sheet shape to fine needle shape.The higher the concentration of magnesium ion,the more fine and broken gypsum crystals,which is not conducive to gypsum dehydration.The effect of 6 kinds of single component scale inhibitors on the nucleation kinetics of gypsum is studied through crystallization experiments.The change trend of scale inhibitor AMPS containing sulfonic acid group is opposite to that of other scale inhibitors containing carboxylic acid group or phosphonic acid group.The scale inhibitors affect the induced time of crystallization,surface energy,nucleation rate,critical free energy and critical nucleation radius of gypsum.The induced time of crystallization,surface energy,critical free energy and critical nucleation radius of gypsum increase under the conditions of scale inhibitors containing carboxylic or phosphonic acid groups;the nucleation rate of gypsum decreases.When the supersaturation ratio is 3,the metallographic microscopy photos of gypsum samples each scale inhibitor condition show that the scale inhibitors change the crystal morphology of gypsum.Among them,the scale inhibitor HPMA containing carboxylic acid group and the scale inhibitor ATMP containing phosphonic acid group appear cluster gypsum under the working conditions.At the same time,the gypsum particle size report shows that the scale inhibitors change the gypsum particle size.In addition to the scale inhibitor AMPS,the gypsum particle size increased under all scale inhibitor conditions.The effect of 7 kinds of composite scale inhibitors from the actual use of power plants on the nucleation and growth of gypsum is studied through crystallization experiments.Compound scale inhibitor prolong the crystallization induction time of gypsum and inhibit the nucleation of gypsum.The higher the concentration of scale inhibitor,the more difficult the nucleation of gypsum.When the scale inhibitor concentration is 10 mg/L,the crystallization induction time of gypsum of gypsum increases by 17%to 48%,and the nucleation inhibition index range from 7%to 17%.When the nucleation inhibition index of scale inhibitor F is minimum,the corresponding gypsum crystallization induction time has the smallest change,and its inhibition of nucleation is the weakest.The morphology of gypsum crystals reflect the performance difference between scale inhibitors.After adding scale inhibitor D,the gypsum crystal appear as flakes.The flakes indicate the complexation and dispersion of scale inhibitor D is strong,and the nucleation of gypsum was seriously inhibited.After adding scale inhibitors F,the gypsum crystal is presented as adhesive sheets and needle coexistence.This shape indicate that the distortion performance of the scale inhibitor F is strong,and the effect of nucleation is low.According to the morphology of gypsum samples with scale inhibitor added after crystallization,scale inhibitor F has the strongest distortion performance.In summary,scale inhibitors with carboxylic and phosphonic acid groups are more likely to cause distortion of gypsum crystals.The complex scale inhibitor with strong distortion performance has weak inhibition effect on the nucleation process of gypsum,and the nucleation inhibition index is small,which is more suitable for the resource utilization of desulfurized gypsum under the background of zero waste water discharge of the whole plant.