The wet smelting plant of Chenzhou Mining Co., Ltd. is a new plant established by Chenzhou Mining during the “11th Five-Year Plan†period. It has three wet process production lines, including the wet oxidized cerium process line with a design capacity of 2000t/a. The wet high-purity cerium oxide product has good quality and extremely low impurity content, and the main impurity elements such as arsenic , lead , iron and copper in the product are all 0.02%. The following is a high-purity environmentally friendly product, which is a key product of the company's development.
With the continuous improvement of the quality requirements of cerium oxide in various industries, the advantages of wet cerium oxide are more and more obvious, and its use range is also wider and wider. The research on its whiteness mainly focuses on the crystal form and impurity content. Influence, there is no research paper on the influence of particle size on whiteness. The author has studied the correlation between particle size and whiteness through a large number of sample statistical analysis, and obtained some meaningful conclusions, which can provide technical guidance for production.
I. Factors affecting the whiteness of wet oxidized bismuth
The effect of impurity ion content on whiteness in barium chloride solution. The main element affecting whiteness in antimony sulfide ore is Sn, and the content of Sn in the barium chloride solution before hydrolysis is greater than 0.01%. It will have a significant negative effect on the whiteness of the product, making the product red, S 2 + , Cu + , Fe 2 + , Bi 3 + plasma, and its negative effect is also large.
The effect of crystal form on the wet oxidation wet oxidation degree. According to the process, the ruthenium chloride directly neutralizes the ruthenium oxide formed by dechlorination, and its crystal nucleus structure is orthorhombic, while the orthorhombic yttrium oxide has strong photosensitivity, and it will be yellow after being exposed to light. Affect the whiteness of the product. Therefore, a certain amount of a transition agent is added in the production to convert the orthorhombic cerium oxide into a cubic crystal form to improve the nucleus stability.
The effect of SbCl 3 hydrolysis on whiteness at higher temperatures. When SbC1 3 is hydrolyzed, there is a yellow hydrolysate of secondary hydrolysate, and the appearance of this substance has a great relationship with temperature, and its amount increases with the increase of hydrolysis temperature. Further, in the next neutralization step, oxonium also has a possibility of reacting with water to form a yellow orthorhombic crystal, and thus a higher hydrolysis temperature is disadvantageous for increasing the whiteness of the active Sb 2 O 3 .
In addition, the particle size of cerium oxide also has an effect on whiteness.
Second, the effect of wet cerium oxide particle size on whiteness
(1) Analysis sample collection
In this research analysis, considering the factors affecting whiteness, in the sampling process, the samples have been screened, the production process conditions are the same, the crystal form conversion is complete, and the main impurity content of the sample is less than 0.01%. The particle size measurement was carried out by using Zhang Ruifu's air permeability method. The whiteness was measured by WSD-3 automatic whiteness meter, and 30 samples were finally selected. The corresponding particle size and whiteness data are shown in Table 1.
Table 1 Sample whiteness and corresponding particle size
Serial number | Particle size / μm | BaiDu/% | Serial number | Particle size / μm | BaiDu/% | Serial number | Particle size / μm | BaiDu/% |
1 | 2.88 | 93.50 | 11 | 2.65 | 94.65 | twenty one | 2.39 | 94.32 |
2 | 1.90 | 93.44 | 12 | 2.45 | 94.43 | twenty two | 3.12 | 93.41 |
3 | 2.62 | 93.58 | 13 | 2.58 | 93.98 | twenty three | 1.88 | 94.02 |
4 | 2.72 | 93.80 | 14 | 2.60 | 94.38 | twenty four | 3.24 | 92.78 |
5 | 2.90 | 93.61 | 15 | 2.87 | 93.91 | 25 | 3.24 | 91.84 |
6 | 2.72 | 94.04 | 16 | 2.79 | 94.10 | 26 | 2.60 | 94.21 |
7 | 2.82 | 93.38 | 17 | 2.56 | 94.32 | 27 | 3.08 | 92.25 |
8 | 3.19 | 92.58 | 18 | 2.87 | 94.03 | 28 | 3.22 | 93.08 |
9 | 3.09 | 93.57 | 19 | 2.70 | 93.74 | 29 | 1.91 | 94.53 |
10 | 3.04 | 92.10 | 20 | 2.81 | 93.72 | 30 | 2.45 | 94.68 |
(2) Statistical analysis of samples
The correlation analysis of the samples was performed by SPSS statistical analysis software (software version: Spss13.0 for windows).
1. The general description of the variables is shown in Table 2.
Table 2 General description of variables
project | Mean | Standard error | Number of samples |
BaiDu | 93.666 | 0.74518 | 30 |
granularity | 2.7297 | 0.37333 | 30 |
As can be seen from Table 2, the average whiteness is 93.666, the standard error is 0.745, the average particle size is 2.7297, and the standard error is ±0.373.
2. The analysis results of correlation are shown in Table 3.
Table 3 Correlation Analysis Table
project | BaiDu | granularity | |
Pearson correlation coefficient | BaiDu | 1.000 | -0.641 |
granularity | -0.641 | 1.000 | |
Unilateral test significance level | BaiDu | 0.000 | |
granularity | 0.000 | ||
Number of samples | BaiDu | 30 | 30 |
granularity | 30 | 30 | |
Table 3 shows that the correlation coefficient between whiteness and particle size is -0.641, P<0.0001, and the difference is extremely significant, that is, there is a correlation between whiteness and particle size.
3. The variance analysis of the regression model is shown in Table 4.
Table 4 shows that the 30 sets of data fit well with the estimated linear model, P < 0.0001, the difference is extremely significant, that is, the estimated regression model is available.
Table 4 Variance analysis table of regression model
project | Total deviation | Degree of freedom | Average dispersion | F value | Significant level |
Regression value | 6.614 | 1 | 6.614 | 19.515 | 0.000a |
Residual value | 9.49 | 28 | 0.339 | ||
total | 16.104 | 29 |
4. The parameter estimates for the regression model are shown in Table 5.
Table 5 Parameter estimation of regression model
project | Non-standardized coefficient | Standardization coefficient | t value | Significant level | |
B | Standard error | β | |||
constant | 97.158 | 0.798 | 121.821 | 0.000 | |
granularity | -1.279 | 0.29 | -0.641 | -4.418 | 0 |
Table 5 shows that the parameters of the regression model are a = - 1.279, the constant b = 97.158, P < 0.0001, that is, the estimated parameters are available, that is, the whiteness and the granularity are statistically consistent with the following equation:
Y=-1.279X+97.158
Wherein X represents the particle size, μm; Y represents whiteness.
5. The scatter plot and its regression line are shown in Figure 1.
Figure 1 Relationship between particle size and whiteness
Figure 1 illustrates that the scatter distribution of the sample data is basically on or near the regression line, and the difference is small.
According to the statistical analysis of the wet cerium oxide sample, the particle size parameter has a close influence on the whiteness parameter, and the linear regression equation can be approximated as Y=-1.279X+97.158, that is, the finer the particle size, the higher the whiteness.
Third, the analysis of the reasons for the whiteness of particle size
Whiteness, also known as brightness, is the impression that a substance acts on the human eye after reflecting the reflected light, indicating the brightness of the substance. Test substance whiteness of magnesium oxide is typically a standard whiteness of 100%, and it is set as the standard reflectance of 100% with respect to the percentage of blue light reflected hydroxide standard sample plate surface to indicate whiteness. The higher the reflectance, the higher the whiteness and vice versa.
Looking at the relevant data, the smoother and flatter the surface of the material (the wet yttria), the more photons reflected back to the light source, which is only a phenomenon that can be observed by the naked eye. When the surface of the material is magnified by a microscope, it is found that the surface of the substance having a high degree of whiteness is actually a plane composed of finely arranged particles of the substance.
When the spacing between the particles is small and the particle diameter is also small, the diffuse reflection phenomenon of the light source on the surface of the material is small, that is, the light reflectance is large, and the whiteness of the material is also high; conversely, when the spacing between the particles is large, When the diameter of the particles is also large, the diffuse reflection phenomenon of the light source on the surface of the material is large, and the amount of photon loss is large, that is, the light reflectance is small, and the whiteness of the material is also low.
Therefore, when the wet cerium oxide particle size is small, the phenomenon of light diffuse reflection at the time of whiteness measurement is small, and the light reflectance is large, and the whiteness of wet oxidized yttrium is also high.
Fourth, starting from the granularity factor to improve the whiteness index
Art improvement measures
The control method of product particle size in the wet cerium oxide process can be improved from the following aspects:
(1) Stirring strength and speed of SbC1 3 hydrolysis have an effect on the size of yttrium oxide nucleus formation (ie, particle size). Under normal circumstances, the faster the stirring and the stronger the strength, the smaller the particle size.
(2) The concentration of SbCl 3 has an effect on the size of crystal nuclei during hydrolysis. Under normal circumstances, the lower the concentration of barium chloride and the same amount of hydrolyzed water, the smaller the particle size, but in practical production applications. The concentration of cesium chloride should be kept at a certain concentration, or the ratio of water to liquid should be adjusted at different concentrations to make the concentration of hydrazine hydrate constant.
(3) The complexing agent is added in an appropriate amount in the hydrolysis step, which can hinder the aggregation of a plurality of crystal nuclei, and actually reduces the particle size of the wet cerium oxide.
(4) Impurity ions have an effect on the particle size, mainly affecting the process of dehydration to form chlorooxon crystals during the hydrolysis of SbCl 3 , thereby affecting the particle size of cerium oxide. Alternatively, the dehydration process is accelerated to obtain crystals of coarse particles; or the dehydration process is slowed down to obtain crystals of fine particles.
Product whiteness can be improved by reducing the wet cerium oxide particle size.
V. Conclusion
The wet cerium oxide particle size has a close influence on the whiteness and the linear regression equation can be used to reflect the relationship between the two. The linear equation can be approximated as Y=-1.279X+97.158, that is, the finer the particle size, the higher the whiteness. While reducing the particle size of the wet cerium oxide, the whiteness also has an increased positive effect.
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