I. Introduction
Potassium feldspar is a potassium rocks, potash potential resources. China's potassium feldspar reserves are huge, mainly distributed in Shanxi, Shandong, Sichuan, Anhui and Xinjiang provinces [1] . The extraction of soluble potassium from potassium feldspar by high temperature thermal decomposition is an important method to develop and utilize potassium feldspar resources. Generally, it is necessary to add decomposition aids for melting, and domestic researchers have done many explorations in this area [2] -5] . The prices of CaCl 2 and NaCl are relatively low, and industrial raw materials can be obtained from waste slag and waste liquid in the soda ash industry, which is less corrosive to equipment and has a relatively high decomposition rate. Based on previous experiments [6] on the binding studies and experiments related metallurgical methods kinetics [7-9], to be adopted in this experiment kinetics CaCl 2 and NaCl were used as the additives mentioned thermal decomposition of potassium feldspar The experiment focused on the influence of the main factors such as reaction temperature, auxiliary ratio and K-feldspar particle size on the chemical reaction rate, so as to better control the chemical reaction process.
Second, the experiment
(1) Raw materials and reagents
Material from Shanxi Wenxi feldspar, anhydrous calcium chloride, sodium chloride, potassium chloride, sodium tetraphenylborate, sodium hydroxide, magnesium sulfate, cetyl trimethyl ammonium bromide, sodium acetate, Glacial acetic acid was analytically pure and 95% ethanol was chemically pure.
(2) Experimental equipment and analytical instruments
PE60×100 jaw crusher , QM-1SP planetary ball mill , KSJD-6.3-16 muffle furnace, SHZ-D(III) type circulating water vacuum filter, XRF-1800 X-ray fluorescence spectrometer , MASTERSIZER2000 laser diffraction particle size analyzer.
(3) Experimental methods
K-feldspar was crushed to a 6 mm with a jaw crusher , ground with a planetary mill for 1 h, sieved with a standard set of sieves, and 50 g of the powder sample was weighed, placed in a 200 mL porcelain crucible, and added with an appropriate amount of auxiliary, stirred and mixed. The mixture was uniformly placed in a preheated muffle furnace, and the calcined product was naturally cooled to room temperature at room temperature, leached with water, filtered, and the potassium content of the filtrate was measured.
The potassium content was determined by the sodium tetraphenylborate-quaternary ammonium salt volumetric method.
The calculation formula of the reaction fraction f is: the mass of potassium oxide in the leachate/the mass of potassium oxide in the potassium feldspar sample.
The chemical composition of the potassium feldspar sample was determined by x-ray fluorescence spectrometry. The operating conditions were: voltage 30-50 kV, current 50-100 mA, and the atmosphere was vacuum.
When the K-feldspar particle size was measured by a laser diffraction particle size analyzer, water was used as a dispersing agent to select a red light absorption rate.
Third, the results and discussion
(1) Analysis of the characteristics of K-feldspar
The chemical composition analysis of K-feldspar samples was carried out by X-ray fluorescence analysis. The results are shown in Table 1. The X-ray diffraction method was used to analyze the properties of K-feldspar samples. The results are shown in Figure 1.
Table 1 Chemical composition of potassium feldspar
SiO 2 | Al 2 O 3 | K 2 O | Na 2 O | Fe 2 O 3 | Rb 2 O | CaO | BaO | Cr 2 O 3 | MnO | NiO | SrO | CuO | |
Quality score | 66.62 | 17.89 | 12.65 | 1.57 | 0.61 | 0.17 | 0.15 | 0.13 | 0.12 | 0.02 | 0.02 | 0.01 | 0.01 |
Figure 1 X-ray diffraction spectrum of potassium feldspar
It can be seen from Fig. 1 that potassium feldspar contains a small amount of albite and quartz . According to the International Diffraction Data Center Database (JCPDS-ICDD) of the Joint Committee of Powder Diffraction Standards, the K-feldspar is a potassium micro-plagioclase, which belongs to the three-slope. Crystal system.
(2) Effect of calcination temperature on decomposition rate
The reaction materials are mixed first, the mass ratio of CaCl 2 to NaCl in the mixing aid is 2:1, the mass ratio of the mixing aid to the potassium feldspar is 1.2:1, and the particle size of the potassium feldspar is -75 μm. The prepared mixture was calcined at temperatures of 973, 1023, 1073 and 1123 K, respectively, and the fractional f of the thermal decomposition reaction of K-feldspar (ie, extraction rate, see Fig. 2) was determined, and the reaction fractions at different reaction temperatures were compared. The reaction times were substituted into different Ginstling-Brundshtein kinetic equations [7] :
1 - f - (1 - f) 2 / 3 = kt (1)
The fitting of the values ​​calculated according to the dynamic equation (1) is basically in line with the linear relationship (see Fig. 3), indicating that the decomposition reaction process conforms to the Ginstling-Brundshtein kinetic equation. Regression of each linear equation by least squares method, the slope of the line is the reaction rate k, and the line of Ink versus 1/T also has a straight line (see Figure 4). According to the Arrhenius empirical formula [10] , the apparent activation energy of the decomposition reaction is 58.6 kJ/mol from the slope of the straight line, and the apparent activation energy [11] of the calcium chloride and potassium feldspar system is 126.94 kJ/mol. The apparent activation energy of sodium chloride and potassium feldspar system [12] is 81.42 kJ/mol, and the apparent activation energy of calcium chloride and sodium chloride mixed system is 68.34 kJ/mol lower than that of calcium chloride system. The system was reduced by 22.82 kJ/mol, which indicated that calcium chloride and sodium chloride were used as mixing aids, which could effectively reduce the apparent activation energy of the reaction system and increase the reaction rate.
Figure 2 Effect of reaction temperature on reaction rate
Figure 3 Relationship between reaction rate and reaction temperature
(Y = 1 - f - (1 - f) 2 / 3 = kt)
Figure 4 Arrhenius diagram of the decomposition reaction
(III) Effect of the ratio of additives on the decomposition rate
The amount of additives added will affect the rate of the K-feldspar decomposition reaction system. This is because when the additive interacts with the K-feldspar particles, it may increase or decrease the number of crystal defects in the K-feldspar, thereby increasing or decreasing the vacancy concentration in the crystal, thereby changing the diffusion rate of the member in the crystal [7] ] . In addition, the auxiliaries may also promote the sintering of the solid surface, making the diffusion process of the material easy, thereby accelerating the reaction process. Under the condition of the K-feldspar particle size of 75μm and the reaction temperature of 1073 K, the mass ratio of the auxiliary agent to the potassium feldspar (assisted ratio) was tested respectively. The results showed that the reaction rate increased with the increase of the auxiliary ratio ( See Figure 5). The mapping of Y to t is basically linear (see Figure 6), indicating that the Ginstling-Brundshtein kinetic model is suitable for the thermal decomposition process of K-feldspar under different additive dosages.
Figure 5 Effect of additive ratio on reaction rate
Figure 6 Relationship between auxiliary ratio and reaction rate
(Y = 1 - f - (1 - f) 2 / 3 = kt)
(4) Effect of particle size on decomposition rate
Since solid particles of different particle sizes have different specific surface areas, and the smaller the particle size of the solid particles, the larger the specific surface area, therefore, for particles of the same quality, the smaller the particle size, the faster the reaction rate. When the ratio of the additive was 1.2 and the calcination temperature was 1073 K, the potassium feldspar of three different particle sizes (see Figure 7) was tested separately, and the relationship between the extraction rate and the reaction time at each particle size was obtained, as shown in Fig. 8.
As seen from Figure 8, as the particle size decreases, the thermal decomposition reaction accelerates.
According to the linear regression of the Ginstling-Brundshtein kinetic equation, the graph basically shows a linear relationship (see Figure 9), indicating that the Ginstling-Brundshtein kinetic model can be applied to the experimental reaction system at different particle sizes. Generally speaking, the shorter the reaction time, The lower the system decomposition rate, the better the kinetic model is applied.
Figure 7 K-feldspar particle size distribution curve
Figure 8 Effect of particle size on reaction rate
Figure 9 Relationship between particle size and reaction rate
(Y = 1 - f - (1 - f) 2 / 3 = kt)
Fourth, the conclusion
Kinetic experiments were carried out on the K-feldspar system with calcium chloride and sodium chloride mixing aids. The results show that the decomposition process is controlled by solid film diffusion at different reaction temperatures, which is consistent with the Ginstling-Brundshtein kinetic equation, according to Arrhenius. According to the empirical formula, the apparent activation energy of the decomposition reaction is 58.6 kJ/mol, which is 68.34 kJ/mol lower than that of the calcium chloride system and 22.82 kJ/mol lower than that of the sodium chloride system, indicating that calcium chloride and sodium chloride are mixed. The auxiliary agent can effectively reduce the apparent activation energy of the reaction system and increase the reaction rate. The reaction rate increases with the increase of the auxiliary ratio. The Ginstling-Brundshtein kinetic model is suitable for the thermal decomposition process of K-feldspar under different additive dosages. The reaction rate increases with the decrease of particle size. Under different K-feldspar particle sizes, the Ginstling-Brundshtein kinetic model can also be applied to the experimental decomposition system. The shorter the reaction time, the lower the decomposition rate of the system, the kinetic model The better the degree of application.
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