Study on ion transport and nucleation mechanism in electrochemical water softening process

doi:10.11949/0438-1157.20240831

Abstract

Abstract:

Electrochemical water softening is a new type of green industrial circulating water scale inhibition technology. In response to the problem that parallel-arranged pole plates cannot effectively utilise OH^- and thus lead to low softening efficiency, an improved pole plate arrangement based on the simulation of the relative motion of circulating water and hydrogen bubbles is proposed. The passive diffusion of OH^- forms a long-term and effective alkaline area, which improves the utilization rate of OH^- and promotes the uniform nucleation of CaCO₃ crystals in the solution. The results showed that Ca²⁺ in the simulated circulating water was nucleated before reaching the cathode plate, and the number of CaCO₃ crystal particles was stable and the maximum size was up to 25 μm at 120 min, and the softening efficiency was up to 108.2 g/(m²·h) at the current density of 120 A/m², the flow rate of the water inlet of 12 L/h, and the initial hardness of 500 mg/L, and the cathode and anode center spacing of 61.5 mm. In this study, the use of air bubble movement and water flow regulation provides an innovative idea for electrochemical circulating water softening.

Key words: electrochemistry, water softening, alkaline region, ion diffusion, nucleation, PIV

摘要：

电化学水软化是一种新型绿色工业循环水阻垢技术，针对平行排列的极板无法有效利用OH^-进而导致软化效率低下的问题，提出了基于模拟循环水与氢气泡的相对运动改进的极板垂直布置方式。通过OH^-被动扩散形成长期且有效的碱性区域，提升了OH^-的利用率，促进了CaCO₃晶体在溶液中均匀成核。结果表明，模拟循环水中的Ca²⁺在到达阴极板之前已经成核，在120 min时CaCO₃晶体颗粒数量稳定且尺寸最大可达25 μm，在电流密度为120 A/m²、入水口流量为12 L/h、初始硬度为500 mg/L、阴阳极中心间距为61.5 mm时，软化效率可达108.2 g/（m²·h）。本研究利用气泡运动和水流调控可为电化学循环水软化提供新思路。

关键词: 电化学, 水软化, 碱性区域, 离子扩散, 成核, PIV

CLC Number:

TQ 085.4

Wei LIN, Jian DU, Chen YAO, Jiahao ZHU, Wei WANG, Xiaotao ZHENG, Jianmin XU, Jiuyang YU. Study on ion transport and nucleation mechanism in electrochemical water softening process[J]. CIESC Journal, 2025, 76(4): 1788-1799.

林纬, 杜建, 姚晨, 朱家豪, 汪威, 郑小涛, 徐建民, 喻九阳. 电化学水软化过程中离子输运与成核机理研究[J]. 化工学报, 2025, 76(4): 1788-1799.

Figures/Tables 13

Fig.1 Schematic diagram of electrochemical water softening experiment device1—replenishment tank; 2—reactor; 3—reservoir; 4—anode; 5—cathode; 6—peristaltic setup; 7—power; 8—circulating cooling water simulation solution; 9—softened water

Table 1 Reagents used in the experiment

试剂	规格	生产厂家
NaHCO₃	500 g/瓶	天津市鼎盛鑫化工有限公司
CaCl₂	500 g/瓶	天津市鼎盛鑫化工有限公司
EDTA-2钠	0.01 mol/L	天津市津北精细化工有限公司
乙酰丙酮	0.975 g/ml	国药集团化学试剂有限公司
pH 缓冲剂	pH=10	上海市仪电科学仪器有限公司

Fig.2 Schematic diagram of SHADOW method field of view selection and simulation of circulating water flow state

Fig.3 SHADOW method bubble shooting

Fig.4 Visualized tracking of OH- diffusion over time (flow rate 12 L/h, current density 80 A/m2)

Fig.5 Distribution of pH in solution at different heights (flow rate 12 L/h, current density 80 A/m2)

Fig.6 Nucleation in the space directly above the cathode plate for different time periods

Fig.7 Calcium carbonate crystallization process

Fig.8 Decrease in hardness with different plate arrangements

Fig.9 Softening rate (a) and energy consumption (b) at different cathode center spacing

Fig.10 Hardness removal rate (a), softening rate (b), maximum hardness removal rate (c) and energy consumption (d) at different current densities

Fig.11 Hardness removal rate (a), softening rate (b), maximum softening rate (c) and energy consumption (d) at different inlet flow rates

Fig.12 Hardness removal rate (a), softening rate (b), maximum hardness removal rate (c) and energy consumption (d) at different initial hardnesses

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