Study On The Compounding Of Reverse Osmosis Scale Inhibitors And The Mechanism Of Enhanced Scale Inhibition

Reverse osmosis is the mainstream treatment process for mine water desalination in China.In this process,due to the high content of calcium and magnesium ions in the water,it is very easy to deposit scaling on the membrane surface,causing serious membrane pollution and continuously increasing the system operating costs.In engineering,scale inhibitors are usually added before the membrane desalination process to inhibit the formation of calcium carbonate scale,but the large amount of chemicals added can easily cause secondary pollution,so the selection and efficient use of environmentally friendly scale inhibitors is an important basis for the improvement of reverse osmosis desalination efficiency.Based on the comparison of the scale inhibition performance of four conventional scale inhibitors,the study was carried out to compound them and select a highly efficient and environmentally friendly reverse osmosis scale inhibitor formulation,combined with scale formation thermodynamics,constitutive crystalline and morphological characterisation and molecular dynamics simulation to elucidate the scale inhibition mechanism,the paper reached the following conclusions:（1）Comparison of scale inhibition performance of conventional scale inhibitors showed that the best scale inhibition rates of polyaspartic acid（PASP）,polyepoxysuccinic acid（PESA）,sodium carboxymethylcellulose（CMC-Na）and maleic anhydride（MA）could reach 67.26%,95.42%,27.64%and 91.91%respectively,among which the best scale inhibition performance was achieved by the combination of PESA and CMC-Na.The optimum process parameters were selected as follows:agent concentration 80 mg/L,calcium ion concentration 240 mg/L,temperature 80℃,Under these conditions,a comprehensive experiment was conducted,and the results showed that the scale inhibition rates of the composite scale inhibitor on simulated water and actual water were 98.66%and 94.44%,respectively.At the same time,the decay rate of the reverse osmosis membrane decreased from 24.87%to 6.24%compared to the original water.（2）The process of CaCO₃ scale crystallization and precipitation was analysed from the thermodynamic point of view,and the order of generation of different crystal types was analysed,among which calcite scale is dense and stable,which is difficult to remove,so the generation of calcite-type CaCO₃ should be inhibited in the scale inhibition process.The crystal structure and morphology of CaCO₃ scale were characterized by X-ray diffraction（XRD）and field emission scanning electron microscopy（SEM）respectively,and the results showed that in the presence of the compound scale inhibitor,the CaCO₃crystals changed from regular cubic structure to irregular spherical shape,indicating that the compound scale inhibitor could cause CaCO₃ crystals to undergo obvious lattice distortion,the grain size decreased,the crystallinity The scale body became soft and fluffy,thus providing excellent scale inhibition effect.（3）The interaction between the compound scale inhibitor and calcite（104）and（110）surfaces was investigated by molecular dynamics simulation.By comparing the binding energy of PESA,CMC-Na and the complex scale inhibitor with the calcite（104）and（110）surfaces respectively,it was further confirmed that the scale inhibition performance of the complex scale inhibitor was better than that of the two alone,because a large number of carboxyl groups in the complex scale inhibitor had strongπ-πinteractions with CO₃^2-on the surface of calcium carbonate,which made the complex scale inhibitor The molecules of the complex scale inhibitor bond with the calcite crystalline surface and occupy the active sites on its surface,effectively inhibiting the formation of calcium carbonate scale.The research results of the thesis can provide a certain theoretical basis for the efficient use of mine water scale inhibitors,which is of great practical significance to enhance the reverse osmosis desalination and recycling of mine water.