Hebei Messi Biology Co., Ltd. stated that the current market for magnesium oxide powder is huge worldwide, and only a few companies in Israel and Japan have this product. Israel is temporarily unable to know its production process due to war and technical confidentiality. The existing technology mixes two magnesium oxides in a ratio of 10:90-80:20, and then pressurizes and crushes the mixture. Magnesium oxide needs to calcine magnesium hydroxide at different temperatures. The process is complicated and needs to be determined by a professional bet specific surface area instrument. Domestic magnesium oxide is mainly based on primary crude products such as light magnesium oxide. If there is a particle size requirement for magnesium oxide, magnesium oxide powder produced by calcining magnesium hydroxide or crushing or sieving the final magnesium oxide powder is generally used, but the magnesium oxide powder obtained by this treatment method has no compressibility.
The present invention relates to a method for preparing magnesium oxide as a food additive, and in particular to a method for preparing magnesium oxide powder suitable for dry granulation, which is a method for preparing magnesium oxide powder with compressibility, high magnesium oxide content, low heavy metal content, and low bulk density. The method comprises the following steps:
(1) using magnesium carbonate as a raw material, grinding magnesium carbonate, and the particle size of magnesium carbonate powder is d90≤50um;
(2) calcining the obtained magnesium carbonate powder at high temperature to generate magnesium oxide powder, wherein the high temperature calcination includes a heating calcination stage and a heat preservation calcination stage, and the calcination temperature of the entire calcination stage is controlled to be 720-850°C, the heating calcination time is more than 1h, and the heat preservation calcination time is 4-10h.
The grinding particle size, calcination temperature, heating calcination time and heat preservation calcination time of magnesium carbonate are set within the above ranges to control the fineness of magnesium oxide powder. During the calcination process, if the calcination temperature is too high, the particle size of magnesium carbonate powder may shrink sharply, if the temperature is too low, magnesium carbonate may not burn fully, and if the heating calcination time is too short, the particle size of magnesium carbonate powder may shrink sharply. Therefore, the magnesium carbonate powder may be fully calcined within the particle size, calcination time and calcination temperature set in the present invention, thereby ensuring the compressibility of magnesium oxide powder.
The magnesium carbonate is ground to make its powder particle size d90 35-50um. When the particle size of the magnesium carbonate powder is within the above range, the particle size of the magnesium oxide powder can be controlled, so that the hardness of the prepared tablets is higher, the tablets do not have sticking phenomenon, and the success rate of tablet manufacturing is improved.
The calcination temperature is 750-800℃. Studies have found that the calcination temperature of the magnesium carbonate powder within the above range can further ensure the full combustion of the magnesium carbonate powder, reduce the calcination cost, and thus reduce the preparation cost of magnesium oxide powder.
The heating calcination time is 1-2h. Studies have found that when the heating calcination time is set within the above range, the magnesium carbonate powder can be fully burned. If the heating calcination time is less than 1h, the particle size of the magnesium carbonate powder will shrink sharply, affecting the particle size of the prepared magnesium oxide powder and its compressibility. If the heating calcination time is extended to more than 2h, this operation is difficult to operate in practice, difficult to achieve, and increases the calcination cost.
The heat preservation calcination time is 4-8h. Setting the heat preservation calcination time within the above range can not only ensure the full combustion of magnesium carbonate powder, but also ensure the compressibility of the prepared magnesium oxide powder, while reducing the calcination cost, which is suitable for industrial production.
The magnesium carbonate is generated by the reaction of magnesium chloride solution and sodium carbonate solution, and the magnesium carbonate is washed and dried to generate magnesium carbonate crystals. According to research, the magnesium oxide powder prepared by the same method using magnesium hydroxide or magnesium sulfate as the raw material is not compressible.
Compared with the prior art, the present invention controls the particle size of magnesium carbonate and the high-temperature calcination temperature and the heating and heat preservation calcination time, thereby controlling the particle size of the magnesium oxide powder generated after calcination, while ensuring the compressibility of magnesium oxide powder, high purity of magnesium oxide, greatly improving the success rate of magnesium oxide powder in tablet manufacturing, and increasing the hardness of tablets, making tablets more convenient to store and transport, thereby reducing the manufacturing cost of magnesium oxide particles.