Silica is a synthetic amorphous silica fine powder with the chemical name Hydrated Silica. Because of its large specific surface area, stable chemical properties, high temperature resistance and dispersibility, it is widely used in rubber, paint, electronics, adhesives and other industries.
There are three methods for preparing white carbon black: gas phase method, precipitation method and dissociation method. The industrial preparation method is nothing but a combination and improvement of these three methods. From solution is novel method for preparing white carbon, comprising a non-metallic mineral method, and product recovery method grasses method. The non-metallic ore method is a method in which a non-metallic ore is used as a silicon source to convert crystalline silica and silicate into amorphous silica to prepare white carbon black.
The amount of bentonite ore in Ezhou is 6,912,200 tons. Among them, the geological degree is 1.158 million tons of proven intrinsic economic resources; the controlled intrinsic economic resources are 3,709,200 tons; the inferred intrinsic economic resources are 1,324,200 tons.
In this experiment, Ezhou bentonite was used as raw material, hydrochloric acid was used as activator and deodorizer. The process conditions for preparing white carbon black were discussed, and the whiteness and particle size of the product were characterized. This experiment has practical guiding significance for actual industrial production, which not only opens up a new way for the effective utilization of bentonite in Ezhou, but also provides a new attempt for the comprehensive utilization of bentonite resources in Ezhou.
First, the test part
Experimental materials. The experiment used Ezhou calcium bentonite ore (6Pu).
Drugs and reagents, hydrochloric acid, analytically pure. Kaifeng Dongda Chemical Co., Ltd. Reagent Factory; sodium hydroxide, analytical grade, Tianjin Guangcheng Chemical Reagent Co., Ltd.; anhydrous ethanol, analytical grade, Sinopharm Chemical Reagent Co., Ltd.; sodium chloride, analytical grade, Sinopharm Chemical Reagent Limited.
Preparation. The preparation process is carried out by non-metal ore dissociation method: the bentonite is activated by HCl and decontaminated, solid-liquid separation is carried out, the filter residue is alkali-dissolved with NaOH to prepare water glass, water glass is diluted with water to an appropriate concentration, and an electrolyte having dispersion is added. The protective alcohol is then neutralized with an acid, aged under a certain temperature condition, filtered, washed and dried to obtain white carbon black.
Second, the results analysis
(1) Discussion on the influencing factors
The effects of acid activation time, hydrochloric acid concentration, sodium hydroxide dosage, surfactant ethanol dosage and electrolyte sodium chloride dosage on white carbon black were investigated by single factor test analysis.
1. Acid activation time. The acid activation is to dissolve the partially ion-exchanged Si-O tetrahedron and the alkali metal, alkaline earth metal and alkaline earth metal cation in the Al-O octahedron in the bentonite crystal in the hydrochloric acid solution. After two processes: 1 soluble cations are released from the mineral; 2 silicon is precipitated as amorphous SiO 2 twice.
The effect of acid activation time on product whiteness and recovery was investigated at 70 ° C. The results are shown in Table 1 and Figure 1.
Table 1 Effect of acid activation time on product whiteness
Activation time / min | 90 | 120 | 150 | 180 |
BaiDu/% | 93.12 | 94.24 | 95.02 | 95.37 |
It can be seen from Table 1 that the longer the acid activation time, the higher the whiteness of the product, but the increase is not large, and the effect is not significant. Figure 2 is basically an S-shaped curve because Si is extracted from the crystal lattice as amorphous SiO 2 , and as the reaction progresses, these amorphous SiO 2 covers the surface between the remaining mineral layers. , slowing down the rate of acid activation. It can be seen from Fig. 1 that the acid activation time is less than 150 min, and the slope of the recovery curve is large. The recovery rate is obviously improved with the extension of time; when the temperature exceeds 150 min, the curve tends to be gentle and the recovery rate does not change much. The acid activation time was 150 min for reasons of reducing energy consumption and reducing costs.
2. Hydrochloric acid concentration. Hydrochloric acid plays a dual role of activation and dedoping during the reaction. When the concentration of hydrochloric acid is 20%, water and hydrogen chloride form the highest azeotropic system under normal pressure. If this concentration is exceeded, the evaporation rate of hydrochloric acid will be significantly accelerated, which is not conducive to the reaction. Therefore, the concentration of hydrochloric acid is controlled within 20%, and the effects of the concentration on the whiteness and recovery of the product are shown in Fig. 2 and Fig. 3, respectively.
It can be seen from Fig. 2 that as the acid concentration increases, the removal effect of the chromophoric ions such as Fe 3 + and Ti 4 + in the sample is better, and the whiteness of the product increases linearly. It can be seen from Fig. 3 that as the concentration of hydrochloric acid increases, the recovery rate gradually increases, and when it is less than 10%, the recovery rate increases rapidly; when it exceeds 10%, the rate of increase becomes slow. The reason for this phenomenon is that as the acid concentration increases, the viscosity of the reaction system also increases, hindering the flow of hydrochloric acid and contact with the bentonite particles, and the reaction does not proceed in depth. Based on its influence on whiteness and recovery rate, the concentration of hydrochloric acid is preferably 20%, the whiteness is 95.46%, and the recovery rate is 31.8%.
3. The amount of sodium hydroxide. The key to preparing water glass by dissolving acid-filtered filter residue with sodium hydroxide is to control the modulus of water glass between 3.0 and 3.5. The ratio of bentonite to sodium hydroxide is 1:q, and the content of SiO 2 after acid activation is generally about 90%, which is determined by the chemical reaction equation:
nSiO 2 +2NaOH = Na 2 O·nSiO 2 +H 2 O
Get: q=w/0.75n
When n = 3.0 to 3.5 is substituted into the above formula, the theoretical addition amount of sodium hydroxide is q = 0.34 to 0.40. Considering impurities such as quartz and errors, the actual amount ranges from 0.3 to 0.42. The effect of sodium hydroxide dosage on product specifications is shown in Table 2. It can be seen from Table 2 that the size of the sodium hydroxide is not allowed to affect the whiteness and recovery of the product, and the test is 0.35 g/g.
Table 2 Effect of sodium hydroxide dosage on product index
Alkali quantity q/(g/g) | 0.33 | 0.35 | 0.37 | 0.39 |
BaiDu/% | 95.43 | 95.54 | 95.32 | 95.13 |
Recovery rate/% | 30.27 | 31.54 | 31.7 | 31.22 |
4. The amount of surfactant ethanol. The basic unit of the water glass prepared by alkali dissolution can be regarded as a tetrahedron having Si as a central atom and -ONa as a vertex. When neutralized with acid, -ONa is converted to -OH, and the resulting silica sol is a particle having a large specific surface area, which adsorbs a large amount of water. When the water loses water, the silicon oxide bonds and rapidly agglomerates into coarse particles, and the surface activity disappears. During the preparation of silica, a certain amount of ethanol is added to form a hydrogen bond with the apex oxygen of the tetrahedron, thereby isolating the vertex oxygen from the water, and reducing the agglomeration of the hydrated silicic acid during drying and dehydration. Therefore, the amount of ethanol added directly affects the particle size of the silica. When the amount of bentonite fed is log, the effect of the amount of ethanol added on the particle size is shown in Figure 4.
During the acid precipitation process, the polycondensation reaction of the silicic acid monomer will form a polymer-like silicon-oxygen bond, and finally a multi-branched polymer will be obtained. The silicon-oxygen bond in the polymer formed by the reaction is combined with the surfactant ethanol molecule. As can be seen from Fig. 5, when the amount of ethanol added is small, only a small number of silicon-oxygen bonds are combined with ethanol, and the white carbon black has a large particle size. The amount of ethanol added increases, and the number of combinations of silicon-oxygen bonds and ethanol increases, which can effectively prevent the particle size of white carbon black from further increasing. When a certain degree is reached, the bonding resistance between the silicon-oxygen bond and the ethanol increases, and the binding efficiency decreases. Therefore, the amount of surfactant ethanol added is preferably 20 mL/g.
5. The amount of electrolyte sodium chloride. In the sodium silicate solution, SiO 2 anion is contained, and the electrolyte sodium chloride is added to carry the cation, which can weaken the electrostatic effect and form a diffusion electric double layer around SiO 2 . When the mutual repulsive force between the positively charged cations of the electric double layer shell is greater than the van der Waals attraction between the colloidal particles, the SiO 2 ·nH 2 O in the colloidal solution is promoted to be in a stable state. Experiments have shown that the addition of electrolyte solution can make the particles of silica become smaller, and the addition amount of electrolyte is generally lower than the critical aggregation concentration; however, if the amount is too much, the amount of gel will increase and the quality of silica will decrease significantly. With this in mind, this test uses NaCI, which has a low electricity price, which has a high critical concentration and is used as a dispersant in the test. Therefore, as the electrolyte is added, the overall particle size is reduced, as shown in FIG. The 0.5 g sodium chloride/log bentonite with the highest efficiency in this interval was selected as the suitable point.
(2) Characterization
1. XRD analysis of white carbon black
As can be seen from Fig. 6, the white carbon black is a broad diffraction peak and is amorphous.
2. Morphological representation
As can be seen from Fig. 7, the silica has a uniform particle size distribution, a minimum particle diameter of 80 nm, and an average particle diameter of about 200 nm. The point, line and surface contact between the white carbon black particles are intertwined to form more micropores, which can significantly increase the specific surface area of ​​the white carbon black and improve the adsorption performance of the product.
Third, the conclusion
(1) The process conditions for preparing white carbon black from Ezhou bentonite are: acid activation time 150 min, hydrochloric acid concentration 20%, sodium hydroxide dosage 0.35 g/g, ethanol dosage 2 mL/g, sodium chloride dosage 0.05 g/g The acid precipitation end point has a pH of 7.
(2) Process parameters such as acid activation time and hydrochloric acid concentration are the main factors affecting the recovery rate. Surfactant ethanol and electrolyte sodium chloride affect the product particle size.
(3) The whiteness of the obtained white carbon black is 95.46%, and the particle size is 200 mm.
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