The Safety Risk Analysis Of Water Purification Materials And The Study On The Law Of Dissolution And Release Of Metal Elements

With the improvement of human health and safety awareness,more and more water purification products have been entered ordinary families.The drinking water is purified by water purification products through filtration,adsorption and disinfection of its components and materials.However,due to the different raw materials,formulations or production processes,some harmful substances such as heavy metals（As,Al,Mn）,inorganics,organics and radioactive substances may exist in the water purification material.The water purification material will be in contact with drinking water for a long time during the normal use of the water purifier,causing harmful substances to gradually dissolve into the drinking water,thereby potentially harming human health.Therefore,in order to ensure the safety of drinking water,it is of great practical significance to study the safety risks of water purification materials in water purification products.This article was based on the domestic standard“Standard for safety evaluation of equipment and protective materials in drinking water system（GB/T17219-1998）”and international standards“Drinking Water System Components-Health Effects（NSF/ANSI 61）”and“Plastics piping systems for the transport of water intended for human consumption-Migration assessment（EN ISO 8795:2001）”to design immersion experiments.The health and safety indicators of common water purification materials on the market were detected and the safety risks of water purification materials were analyzed.By controlling temperature,pH and residual chlorine concentration to simulate sudden water quality conditions,the dissolution law of metal elements in water purification materials under different immersion conditions was studied.Combined with the results of scanning electron microscope and energy spectrometer,the reasons for changes in the microstructure and material composition on the surface of the water purification material caused by different acid-alkali conditions were analyzed.The dissolution mechanism was also analyzed by dissolution kinetics.The research conclusions were as follows:（1）The immersion experiment was conducted on 6 types of water purification materials,and the health and safety indicators were tested and analyzed.As a result,it was found that a number of indicators in the water purification material failed to be tested:the turbidity,TDS and TOC of the conventional indicators were frequently exceeded;the dissolution of 18elements was detected in the heavy metal indicators,and the dissolution concentration of Al,Ti and As exceeded the standard and the dissolution concentration of Zn,Mn and Ba elements was also close to the standard safe concentration limit;although the dissolution concentration of organics did not exceed the standard,dozens of trace organics were detected in the body of the material,some of which were listed in the“List of 129 Priority Pollutants in the US EPA Water Environment”,“169 Items of the Latest SVHC Highly Concerned Substance List”,and“Priority in Chinese Water Involved in the Control of Pollutants Black List”.This showed that the common water purification materials on the market had certain safety risks.（2）By adjusting the pH,temperature and residual chlorine to simulate the sudden water quality conditions that may occur after a long-term operation,the standard addition experiment was conducted to detect dissolution of metal elements in the immersion solution.The results showed that the metal elements in the water purification materials had exceeded the standard of dissolution concentration under different immersion conditions:pH had a significant effect on the dissolution of elements,the dissolution concentration of Al,Mn,Ba,Ti,Fe,Zn,Cd,As exceeded the standard under strong acid conditions and that of Al,Fe,As,Ti exceeded the standard under strong alkali conditions;temperature also had a significant effect on the dissolution of elements,the dissolution concentration of Al,Zn,Mn,Ti and As exceeded the standard under high temperature conditions;the change of residual chlorine concentration would cause significant fluctuations in the element dissolution concentration of the water purification material,and Ti,Al,Se and Fe exceeded the standard.（3）According to the material composition,preparation process and purification mechanism of the material itself,the dissolution law of the four exceed-standard elements Al,Mn,As and Zn in the water purification material under acid-alkali conditions was explained.Combined with the results of scanning electron microscopy and energy spectrometer,the reasons for the change in microstructure and element composition on the surface of the water purification material caused by different acid-alkali conditions were analyzed.It was found that the strong acid-alkali conditions have a strong corrosive effect on the surface of the water purification material,and the specific surface area of the material was increased,making it easier for metal elements to dissolve from the material into the immersion solution.In addition,due to the different material composition,preparation process and migration mechanism of water purification materials,the element dissolution concentration was obviously different.At the same time,combined with the analysis of dissolution kinetics,it was found that the element dissolution was mainly controlled by ion diffusion,which could be descried by the kinetic equation 1-（2/3）X-（1-X）^2/3=α₁t.