The chemical formula of dolomite is CaMg(CO3)2, which is rich in resources and is an important calcium and magnesium raw material. The main application fields of dolomite include building materials, chemistry, agriculture, environmental protection, etc. However, the utilization of dolomite is still low at this stage. Typical utilization methods, such as mechanical crushing into stone powder, and calcination as soil conditioner or gas adsorbent will cause the loss of calcium and magnesium resources. In order to improve the utilization value of dolomite resources, dolomite needs to be deeply processed to produce high-end magnesium-calcium materials, such as calcium carbonate whiskers and cubic-like calcium carbonate.
There are three crystal forms of calcium carbonate, namely calcite, aragonite, and vaterite. Among them, the calcite type is the most stable thermodynamically, while the vaterite and aragonite types are both unstable and prone to crystal transformation. In the calcite calcium carbonate family, the cubic calcium carbonate is very popular in the market. As an inorganic filler, it has excellent properties such as good dispersibility and uniform particle size, so it is widely used in rubber, paper, medicine and other fields. At present, the synthesis methods of cubic calcium carbonate mainly include carbonation method, gap bubbling method, digestion method and so on.
Deng Xiaoyang et al. used lightly burned dolomite powder, ammonium chloride and carbon dioxide as raw materials, and prepared cubic-like calcium carbonate through the process of ammonia distillation and calcium precipitation without the use of crystal form control agents. The effects of reaction temperature, calcium ion concentration in solution, aeration rate, stirring speed and aging time on the calcite phase content and crystal morphology in calcium carbonate were studied, and the crystal form control mechanism of the precipitation reaction was explored. the result shows:
(1) The optimal reaction conditions are: the reaction temperature is 40℃, the Ca2+ concentration is 0.05mol/L, the carbon passing rate is 100mL/min, the stirring speed is 400r/min, and the aging time is 2h. Under these conditions, cubic-like calcium carbonate crystals with regular morphology, average particle size of 5-10 μm and uniform distribution were prepared.
(2) The degree of unsaturation of the solution has a great influence on the change of the crystal form of calcium carbonate. With the increase of gas-liquid mass transfer rate, the unsaturation of the solution will increase accordingly, and high unsaturation is beneficial to the formation of vaterite crystals. Vaterite is not stable under lower unsaturation, which is favorable for the formation of aragonite crystal form and calcite crystal form.
Compared with other traditional methods, this study prepared calcite crystal calcium carbonate with more regular morphology and better dispersion than other methods without using crystal control agent. In addition, the process is a recycling process, and the waste liquid in the process can still be recycled to participate in the reaction. Therefore, this process has broad application prospects in industry.