Study On The Simultaneous Removal Of Fluoride And Heavy Metals From Groundwater By Induced Crystallization

Fluorine is a necessary trace element in the human body which is widely found in nature.The lack and excessive of fluoride in the body are harmful to human health.The presence of heavy metal elements such as copper,zinc,chromium and iron and trace elements in the human body are limited,but it is closely related to people’s survival and health.Excessive,insufficient,unbalanced or deficient intake of trace elements can cause abnormalities or diseases of the human body in different degrees.Therefore,the content of fluorine and heavy metals in groundwater is very important for drinking.In this study,induced crystallization was used to simultaneously remove fluorine and other heavy metal elements such as zinc,chromium and copper in groundwater.The paper studied the removal characteristics of fluoride and heavy metals in groundwater by natural fluorapatite in the experimental case,and fluorine and heavy metals are removed by simultaneously adding calcium ions,phosphate ions,and ferrous ions to water to control the addition ratio of various ions.In addition,XRD,SEM,XPS and other test methods were used to study the surface structure and material composition of fluoroapatite before and after reaction,and to analyze the mechanism of simultaneous crystallization removal of fluorine and heavy metals.The main conclusions are as follows:（1）10.00 mg/L of copper ions were added to the fluorine-containing 4.75 mg/L water,and fluoroapatite 100 g/L was used as the induced crystal seed crystal.The reaction parameters were as follows:Ca Cl₂·2H₂O and Na H₂PO₄·2H₂O were added,and the control the Ca:P:F molar ratio was 12:6:1 after agent and raw water were mixed.The reaction was carried out for 60 min at 100 rpm/min,and the effluent was measured.The fluoride ion and copper ion concentrations all meet the drinking water quality standards.（2）5.20 mg/L Cr⁶⁺and 6.50 mg/L Zn²⁺were added to the fluorine-containing 4.75mg/L water,and fluoroapatite 50 g/L was used as the induced crystal seed crystal.The reaction parameters were as follows:Ca Cl₂·2H₂O and Na H₂PO₄·2H₂O were added,and the control the Ca:P:F molar ratio was 12:6:1 after agent and raw water were mixed.After reacting for 30 min at 100 rpm/min,22.4 mg/L Fe²⁺ions were added,stirring at400 rpm/min for 1 min,then running at 100 rpm/min for 29 min,so that the total running time was still 60 min.The experimental results show that the effluent fluorine concentration is less than 1.00 mg/L,and the concentrations of metal elements such as iron,zinc and chromium are in line with the national drinking water quality standards.（3）SEM-EDS,XRD and other analytical testing methods were used to analyze the main components of the seed crystal including calcium fluorophosphate,calcium magnesium carbonate,calcium carbonate and so on.Comparing the surface element composition of the seed crystal before and after the reaction,it was found that in the synchronous removal experiment of fluorine copper,there was obvious copper element on the surface of the seed crystal after the reaction.And XRD analysis indicates that there are copper fluorophosphates.It can be inferred that part of the copper in the reaction is adsorbed by the seed crystal,and part of it is removed by inducing crystallization.In the simultaneous removal experiments of fluorine and chromium,iron and zinc,it can be found by SEM,mapping and other analytical methods that there are obvious three types of metals on the surface of the seed crystal after the reaction,and the surface seed crystals have good adsorption properties for chromium,iron and zinc.