可溶性钙盐沉淀法处理含氟废水的热力学分析及应用设计

Thermodynamic Analysis and Comprehensive Utilization Design of Fluorine-Containing Wastewater Treatment Using Soluble Calcium Salts Precipitation

摘要:

针对可溶性钙盐处理含氟废水的工艺过程较为复杂，且处理效果存在不确定性问题，通过热力学分析，研究了可溶性钙盐沉淀反应处理含氟废水的过程，揭示了去除F^-过程的化学和物理现象，由此设计出两阶段可溶性钙盐处理含氟废水工艺。通过推导出的残余F^-含量与Ca²⁺浓度的平衡关系式，计算出残余F^-含量低至1.91 mg?L^-1，明显低于国家现行的污水处理排放标准。含氟废水两阶段处理工艺：第一阶段，将待处理含氟废水的pH值调整至5.0—6.5，边搅拌边加入氯化钙，其加入量为理论计算总量的1/4，搅拌10 min后静止30 min；第二阶段，将经第一阶段处理后的污水pH值调整至7.5—8.5，加入剩余的氯化钙，搅拌30 min后静止20 min，再加入400 mg?L^-1的聚合氯化铝絮凝剂。结果表明，当氯化钙药剂的实际添加总量为理论计算添加总量的82.29%时，采用两阶段可溶性钙盐处理工艺可去除含氟废水中99.88%的F^-，残余F^-的含量为3.33 mg?L^-1，符合国家现行的污水处理排放标准。当含氟废水中F^-含量大于100 mg?L^-1时，随着可溶性钙盐添加量增加残余F^-含量迅速下降；而当含氟废水中F^-含量小于100 mg?L^-1时，随着可溶性钙盐添加量增加Ca²⁺与F^-反应的速率减慢，残余F^-的含量下降趋缓。可溶性钙盐处理偏碱性含氟废水时，适当提高处理后污水的pH值有助于降低残余F^-的含量，同时也能相应地减少Ca²⁺的添加量。若含氟废水处理后的pH值小于处理前时，其pH值下降越少，添加可溶性钙盐的量亦越少。因此，pH值是影响Ca²⁺添加量及处理结果的重要因素。

Abstract:

The process of treatingfluorine-containing wastewater by adding soluble calcium salts is complex， and the treatment effect is uncertain. By analyzing the thermodynamics of calcium salts precipitation reactions in the treatment of fluorine-containing wastewater， this study reveals the chemical and physical phenomena of fluoride removal process . It is calculated that the residual fluorine ion content after treatment can be as low as 1.91 mg?L^-1. A formula for calculating the amount of fluorine ion added was established. The designed fluorine-containing wastewater treatment process is divided into two stages： the first stage involves adjusting the pH value of fluorine-containing wastewater to 5.0—6.5 （acidic dissolving one-quarter of the theoretically calculated amount of calcium chloride in water， adding it to the wastewater under stirring for 10 min， and then allowing it to stand for 30 min. The second stage adjusts the pH value to 7.5—8.5 （alkaline）， adds the remaining calcium chloride， stirs for 30 min， and let it rest for 20 min before adding 400 mg?L^-1 of aluminium chlorohydrate flocculant. The results show that when 82.29% of the theoretical dosage of calcium chloride is added， 99.88% of fluoride ions are removed， resulting in a residual fluoride ion content of 3.33 mg?L^-1， osignificantly lower than the current national wastewater treatment and discharge standard. When the fluorine ion content of wastewater exceeds 100 mg?L^-1， the residual fluorine ion content decreases rapidly with increased calcium salt addition. Conversely， when the fluorine ion content is less than 100 mg?L^-1， the decrease in residual fluorine ion content slows as calcium salt addition increases. Properly increasing the pH value of treated wastewater can help reduce residual fluoride ion content and calcium ion addition if the pH value is higher post-treatment than pre-treatment. If the pH value decreases post-treatment， a smaller decrease results in less calcium salt addition. Therefore， pH value is an important factor affecting calcium salt addition and the treatment outcomes.