Thermodynamic Analysis and Comprehensive Utilization Design of Fluorine-Containing Wastewater Treatment Using Soluble Calcium Salts Precipitation
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.
solublecalcium saltprecipitation reactiontreatmentfluorine-containing wastewaterthermodynamicsprecipitatepH value
万方数据
维普
