The Preparation Of Mineral Water Treaments Additive And Its Discussion Of Adsorption Mechanism Of Residual Chlorine From Tap Water

With the improvement of life quality, people become to focus on the safety and health of drinking water. Chlorine disinfection could insure the safety of drinking water, however, excessive residual chlorine may affect the taste and odor of water, on the other hand, it can threaten people’s health because of chlorine disinfection byproducts(CDBPs) resulted from reaction between Cl2 and nature organic materials in water. The researchs about removal of chlorine residual are lack and have some shortcomings, so they aren’t applied widely. After all, it’s an urgent to supply healthy water or excellent water treatment technology.The aim of this research is to prepare water treaments, ie, modified diopside, that can adsorb the chlorine residual and supply mineral elements. Diopside is silicate mineral that rich in silicate and calcium elements, which contains few harmful impurities. After calcined, diopside is virgineous. So it’s desired raw material to make water treaments.Diopside was the main material. XRF, XRD and TG-DSC were used to characterize the chemical composition and thermodynamic property of diopside. Diopside was calcined at 600℃,700℃,800℃,900℃,1000℃,1100℃ respectively, then the raw and calcined samples were dissolved into deionized water as 2 g/L. The solubility, p H, available Si, Ca and Mg of solution were tested. The results reveal: p H is all above 8.7, the maximum reaches 10.02; the other indexes reach maximum at 700℃. The Si, Ca and Mg can be actived by heat treatment, but the results are not desired, so other materials need to be added.To improve the activity of diopside, i.e the concentration of Si, Ca and Mg, Ca CO3 was added to induce the reaction : Ca Mg Si2O6 + Ca CO3 Ca2 Mg Si2O7 + CO2↑. Akermanite is nesosilicate mineral, its bond energys of Si-O、Ca-O、Mg-O are smaller than that of diopside, which makes it more active when dissolved. Focusing on preparing modified diopside in the base of that theory, three factors including calcining temperature and time, material ration were mainly discussed. Considering the solubility and silicic acid concentration comprehensively, the optimum condition is: n(diopside) :n(Ca CO3) = 1 : 1, the materials are calcined at 1100℃ for 1hour. When the materials are dissolved into deionized water as the ration of 1 g : 250 m L, the solubility reaches 17.21%, the concentration of H2 Si O3 is 21.59 mg/L, p H is 8.38.The materials prepared at the optimum condition was called modified diopside following. The XRD figures reveal island akermanite appears in the samples at 1100℃and 1150℃. Modified diopside was used to remova residual chlorine from tap water, initial residual chlorine concentration, adsorption time and temperature, adsorbent does were studied, The best initial concentration is 4.33 mg/L, equilibrium is obtained in 30 min. The optimum temperature is 30℃, and the best adsorbent dose is 7.5 g/l. The equilibrium dates have preferable correlation to both the Freundlich and Langmuir isotherm models, and the maximum monolayer adsorption capacity is 6.974 mg/g. Thermodynamic analysises ΔG0 < 0 and ΔS0 > 0 indicate the sorption process is spontaneous and entropy generation. From 293 K to 303 K, the ΔH0 = 3.43 k J/mol, so it is endothermic; while from 303 K to 313 K, the ΔH0 =-9.00 k J/mol, this process is exothermic. Judging from the ΔH0, this adsorption belongs to physical types and the main forces are hydrogen bonds and dipole bonds.The kilchoanite appears in the XRD patterns of adsorption residues, the SEM pictures shows the surface of modified diopside before and after adsorption is obviously changed, and Cl O- is found in XPS of adsorption residues. Taking thermodynamic analysis and several characterizations into account, the adsorption mechanism of residual chlorine is the exchange between hydroxyl of kilchoanite and Cl O-, hydrogen bonds are the key forces.The residual chlorine concentration drops to 0.140 mg/L when modified diopside dissolves in tap water, this concentration is under the maximum 4 mg/l, and above 0.05 mg/L in pipe network bottom(GB5749-2006).Desorption experiments were carried out to study the effect of different initial residual chlorine concentration and adsorbent does on desorption rate, the p H of desorption solution was varying from 6.5 to 8.5. The desorption rates are all very low, which indicates this adsorption is stable.