Study On Silicate Species In Citric Acid Solution

The silicate species in water solution could be divided into monosilicic acid （n（polymerization degree）=1）, low polysilicic acid （1<n≤3）, middle polysilicic acid （3<n≤8）and high polysilicic acid （n>8）. The purpose of this research is to study the silicate species inCA solution. Firstly, the analysis of silicate species in high concentration CA solution basedon spectrophotometry and gas chromatography （GC） was established in this work. Secondly,the relationship between total silicon concentration and CA solution, solution temperature wasinvestigated systemtically, and the silicate species transformation and distribution change wasobtained. The main results of this paper were summarized as follows:1. C_（Si）（the total silicon content）≤200mg·L^-1, the monosilicic acid and low polysilicicacid content in CA solution could be analyzed by spectrophotometric analysis method;200mg·L^-1<C_（Si）≤1000mg·L^-1, the monosilicic acid, low polysilicic acid and high polysilicic acidcontent in CA solution could be analyzed by gas chromatographic analysis method.1) C_（Si）≤200mg·L^-1, the analysis of the monosilicic acid and low polysilicic acid contentin high concentration CA solution based on spectrophotometry was established. The effect ofCA concentration and ammonium molybdate （AM） amount on absorbance was analyzed indetail:i Monosilicic acid analysis: CA could react with AM to form complex in acid solution,but the color reaction of monosilicic acid and AM could proceed quantitatively at the optiamalreaction condition which was ω_（CA）/ω_（AM）≤1/3below3.0%of CA solution. The linear range ofstanrdard curve was1.0～16.0mg·L^-1, and its equation was expressed as A=0.060C+0.030（Ais the absorbance and C is the mass concentration of silicon, R²=0.9982）.ii Total silicon analysis: The polysilicic acid could react with NaF-AlCl3(C_F^-/C_Al³⁺=2) todepolymerized into monosilicic acid within20min, and the total silicon content could beanalyzied by spectrophotometric analysis method.iii Low polysilicic acid analysis: Monosilicic, disilicic and trisilicic acid could react withAM to form heteropoly compound successively, and the accomplish time for coloration ofthem were tM=5min, t_D=46min, tT=267min respectively at303K. The mass concentration oflow polysilicic acid and aborbance statisfied the equation as An-An^-1=0.060C_n+0.030（2≤n≤3）.The spectrophotometric analysis method was applied to accurate determination silicatespecies in CA soulution in this work.2)200mg·L^-1<C_（Si）≤1000mg·L^-1, the quantitative analysis of silicate species in CAsolution by GC-MS was investigated and the analysis of monosilicic acid, low polysilicic acidand middle polysilicic acid in CA solution was established with n-tetradecane as internalstandard. The effect of trimethylsilyl reagents, solvents and resins on trimethylsilyl reaction inCA solution was analyzed in detail: the optimal trimethylsilyl reagents are hexamethyldisiloxane and the optimal resin was Amberlyst15with acetone as solvents. The GC analysismethod was applied to accurate determination monosilicic acid, low polysilicic acid andmiddle polysilicic acid in CA soulution in this work. 2. Based on spectrophotometric and gas chromatographic analysis method, therelationship between total silicon concentration and CA solution, solution temperature wasinvestigated systemtically, and the silicate species transformation and distribution change wasobtained.1) The C_（Si）≤1000mg·L^-1could be divide into five zones by F which reprented the slopeof linear equation of monosilicic acid percentage content and total silicon content. There werebig differnences among the silicon speicies in five zones:ZoneⅠ（only monosilicic acid existed）, monosilicic acid had no transformation;ZoneⅡ（monosilicic and disilicic acid existed）, monosilicic acid transformed to disilicicacid;ZoneⅢ（monosilicic, disilicic and trisilicic acid existed）, monosilicic acid transformed todisilicic and trisilicic acid;ZoneⅣ（monosilicic, low polysilicic and middle polysilicic acid existed）, monosilicicacid transformed to low polysilicic and middle polysilicic acid;ZoneⅤ（monosilicic, low polysilicic, middle polysilicic and high polysilicic acid existed）,monosilicic acid transformed to low polysilicic, middle polysilicic and high polysilicic acid.2) The silicate species in ZoneⅠwas unaffected by CA and solution temperatutre. Whenthe CA concentration was improved from0%to50%, the value of F increased evenly. Thesequence of increasing extent was Ⅳ>Ⅲ>Ⅴ>Ⅱ, so the CA ability of inhabitingpolymerization of monosilicic acid was Ⅳ>Ⅲ>Ⅴ>Ⅱ; When the solution temperature wasimproved from278K to278K, the value of F decreased at different rates in278³18K and318³58K and the value of F decreased evenly between Ⅲ and Ⅴ. The sequence ofdecreasing extent was Ⅳ> Ⅱ （318³58K）> Ⅲ> Ⅱ （278³18K）> Ⅴ, so the solutiontemperature ability of promoting polymerization of monosilicic acid was Ⅳ>Ⅲ>Ⅱ>Ⅴ.3) There was a good linear relationship between CA concentration and critical siliconconcentration （CSC）, which the value of F changed exactly. The linear equation could beapplied to predict silicate species with known total silicon and CA concentration at298K;there was a good linear relationship between solution temperature and CSC. The linearequation could be applied to predict silicate species in30%CA solution with known totalsilicon concentration at278³58K.4) The CA concentration was improved from0%to50%, and the variation range of themonosilicic acid percentage content in five zones were0%,0%⁵%,3%⁹%,10%²0%and14%²1%. So the monosilicic acid percentage content in zoneⅤwere influenced greatly byCA concentration; The solution temperature was improved from278K to358K, and thevariation range of the monosilicic acid percentage content in five zones were0%,-7%⁰%,^-16%^-7%,-25%^<sup>-16%and-39%^-31%. So the monosilicic acid percentage content inzoneⅤwere influenced greatly by temperature.