White cement is a commonly used building decoration material, which belongs to a kind of Portland cement. However, because it must have high whiteness, it has high requirements for the production process and raw materials. This post focuses on the influence of raw materials and fuels on the whiteness of white cement, and the quality requirements of raw materials and fuels in the production of white cement.
Requirement of White Cement Raw Material
The mineral composition of white cement clinker is basically the same as that of ordinary portland cement (OPC) clinker, mainly C3S and C2S. The difference is that there is little iron phase mineral C4AF in white cement clinker, which is because Fe2O3 has a great impact on the whiteness of cement. Only by strictly limiting the content of Fe2O3 in raw materials and fuels can we meet the production requirements of white cement.
Therefore, white cement plants often use high-quality limestone as raw materials and mix with silica raw materials such as pyrophyllite, feldspar, silica, kaolinite, and quartz sand to produce white cement.
| W(Fe2O3)/% | 3.0~4.0 | 0.45~0.70 | 0.45 | 0.40 | 0.24 | 0.15 |
| Whiteness/% | 70 | 78 | 83 | 85 | ||
| Colour | dark gray | light green | white | white | white | white |
Mineralizer
The calcination temperature of white cement clinker is higher than that of ordinary portland cement clinker, reaching 1500 ~ 1600 ℃. In order to reduce the calcination temperature, white cement plants usually add CaF2 as a mineralizer to the raw materials. Some plants also use fluorine or sulfur industrial waste residue as mineralizers.
Mineralizers can reduce the calcination temperature of white cement clinker by reducing the decomposition temperature of carbonate, accelerating the solid-phase reaction, and reducing the viscosity and formation temperature of liquid phase. In the production process of white cement, mineralizer also has a certain degree of whitening effect. Its dosage should be controlled below 5%.
Alkali
In the production of ordinary portland cement (OPC), the alkali in raw materials is a harmful volatile substance; However, in the production of white cement, an appropriate amount of alkali content in raw materials can improve the quality of white cement clinker. This is because an appropriate amount of alkali can reduce the lowest common melting point of white cement raw meal system, increase the amount of liquid phase and improve the burnability of white cement raw meal. Moreover, K + and Na + in alkali can change the state of some coloring ions and improve the whiteness of the white cement clinker.
Requirement for Fuel
The KH, SM, and IM of white cement raw meal are very high, so white cement raw meal needs a high calcination temperature, which requires that the fuel used for calcination has a high calorific value and can burn rapidly and completely to ensure sufficient calcination temperature.
In addition, in order to ensure the whiteness of cement, the Fe2O3 content brought in by fuel should be as little as possible.
According to this consideration, the most suitable fuel for the production of white cement is heavy oil and natural gas, and coal should be avoided using as fuel.