| Circulating cooling water is widely used in many industrial processes,such as power generation,petrochemical industry and steel manufacturing.The circulating cooling water contains high concentration of hardness ions,including calcium ions and magnesium ions.In the circulating cooling water system,scaling can reduce the thermal efficiency,block the pipeline and shut down the equipment.Therefore,the scaling of circulating cooling water is a long-term concern in water treatment industry.At present,various methods of stabilizing water quality and descaling often ignore problems,such as secondary pollution,chemical waste and tedious operation.In recent years,electrochemical water softening technology has attracted great attention due to its environmental compatibility and multi-function.Based on previous research,the electrochemical water softening technology without secondary pollution,high efficiency and simple operation is adopted to explore the optimal conditions for the preparation of calcium carbonate whiskers in circulating water system,meanwhile realizing the effective removal of hardness.In this paper,stainless steel mesh was selected as cathode material,so that calcium carbonate whiskers can be deposited and attached to the cathode surface.Using calcium chloride and sodium bicarbonate as electrolytes and magnesium chloride as crystal form control agent,the effects of voltage and time during nucleation period,voltage and time during crystal growth period,reaction temperature,electrolyte concentration,crystal form control agent concentration and flow rate on the preparation of calcium carbonate whiskers were studied.The best preparation conditions of calcium carbonate whisker were investigated by SEM,XRD and EDS.The formation and growth of calcium carbonate whiskers were monitored by chronoamperometry and electrochemical impedance spectroscopy.In addition,through the electrolytic treatment of simulated circulating cooling water,this paper expounds the scale removal and scale inhibition mechanism of electronic water treatment technology,explores the influences of various factors on the scale removal,evaluates the influence mechanism of various factors on water quality,and optimizes the scale removal effect.The results showed that when the mesh number of stainless steel was 1200,the concentration of calcium chloride and sodium bicarbonate were 600 mg/L and 300 mg/L,the concentration of crystal control agent magnesium chloride was 150 mg/L,the voltage of nucleation period was 18 V,the nucleation time was 5 min,the crystal growth voltage was 2 V,the crystal growth time was 55 min,the reaction temperature was 70℃,and the flow rate was 6 mL/min,the morphology of calcium carbonate whiskers was the best.The length and diameter of the whiskers were 18.80 μm and 0.76 μm,respectively.And the length diameter ratio was 24.74.According to the analysis of the growth process of calcium carbonate whiskers prepared by electrochemical method,calcium chloride and sodium bicarbonate could react rapidly in 1.3 s and deposited on the cathode surface.On the chronoamperometric curve,the current intensity decreased to the minimum within 1.3 s,and basically remained unchanged.The reaction was in the equilibrium state of diffusion and consumption of Ca2+ and CO32-.Finally,the simulated circulating cooling water was electrolyzed by electrochemical method.The results showed that the voltage during nucleation period,nucleation growth time,reaction temperature and magnesium chloride concentration were consistent with the optimal conditions for the preparation of calcium carbonate whiskers.The other factors affecting the removal of calcium ions were calcium chloride concentration of 300 mg/L,sodium bicarbonate concentration of 1800 mg/L,nucleation time of 20 min,crystal growth voltage of 1 V and flow rate of 3 mL/min.In addition,the preparation of calcium carbonate whiskers also verified that the fundamental conditions for the growth of thermodynamic metastable aragonite phase calcium carbonate whiskers include:①The water temperature is higher than 70℃.The higher temperature makes the calcium carbonate whisker cross the lowest energy barrier and provide one-dimensional whisker growth nucleus.②Low calcium carbonate supersaturation.The concentration of calcium chloride is 600 mg/L and the concentration of sodium bicarbonate is less than 300 mg/L.Low supersaturation of calcium carbonate makes aragonite phase dominant in the competitive nucleation process,which can inhibit the formation of two-dimensional calcite phase crystal.③Magnesium chloride(150 mg/L)can effectively reduce the supersaturation of the solution,which is conducive to the growth of calcium carbonate whiskers. |
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