The Preparation And Analysis Of Series Of New Special Magnesium Oxide Products

Magnesium and magnesium alloy being known as "green engineering materials in the 21st century" is being widely studied. Magnesium compound (referred to as magnesium salt) is one of the important products in the inorganic salt, it is also important export products, it takes much economical role in national economy. As one of the important raw material for extracting magnesium, brucite is a very precious non-metallic mineral with high magnesia. The black powder which dropped from manufacturing oriented silicon steel sheet is rich of large amount of MgO. How to recycling and reusing them to prepare magnesium series products, is a very meaningful thing to resources and environmental protection. Special magnesium oxide contains active magnesium oxide, heavy magnesium oxide, nano magnesium oxide, silicon-steel grade magnesium oxide, high purity magnesia, medical magnesium oxide and so on.This paper includs three parts, the first two parts use brucite as raw material, one applies one-step calcination method to prepare high active MgO. This method is green, economical and environmental. The other uses sodium hydroxide as precipitant, without any additives, to prepare capsule heavy MgO. Recycle and resue the black powder which dropped from manufacturing oriented silicon steel sheet. With ammonia as precipitant, we use hydrothermal method to manufacture nano-sized flake magnesium hydroxide and small spherical magnesium oxide particles. Now the main research contents will be described below:1. Preliminary exploration of manufacturing high active MgO by brucite using one-step calcination method.In industry, the preparation of active magnesium oxide are usually obtained by calcination of the precursors. Directly using brucite as precursors, one-step straight calcined method is used to prepare of highly active magnesium oxide. The control variable method is adopted to discuss the influence of different calcined conditions on the weightlessness rate (%), citric acid activity (CAA value/s) and iodine adsorption value (g/mg) and hydration rate (%) of product. The study found that:The activity of obtained MgO which calcined under 550℃-650℃ for 60-100min is the relatively highest, its value of CAA is the least, with 18.4s, value of iodine adsorption is the largest, with 116 mg/g, and the hydration rate is also the highest, these are fully meet the definition of highly active magnesium oxide in industry. Also found that the SEM figure of MgO product calcined in the 600℃ for 90min is cotton wool style, its magnesium hydroxide particles after hydrolysis is very small, and SEM figure also presents cotton wool shaped.2. Research of preparation of heavy magnesium oxide by brucite-alkaline methodAlthough the study of heavy magnesium oxide is relatively less, but in industrial use should not be ignored. After brucite was acid dissolved, using sodium hydroxide as precipitant with different material ratio to prepare magnesium hydroxide precursor, then calcined to MgO under different calcined conditions. Discuss the influence of material ratio, calcined temperature and time on vibrated packing density and activity of product. The results showed that:by controlling different material ratio and calcined conditions, we can obtain capsule shaped heavy MgO whose bulk density can reach to more than 1, however the other way is very difficult to achieve this. When precipitated under the ratio of sodium hydroxide and brucite is 1.25～1.75, after dried and then calcined with 600-750 ℃, the value of m/V of obtained MgO is the largest, can reach more than 1.15, And the crystal structure of the product is stable, with less impurity, so it meet the demand of industrialized production.3. Recycle and reuse used MgO to prepare ultrafine flake-like magnesium hydroxide and spherical magnesium oxideWhen steel plant produce oriented silicon steel sheet, it will fall off much black powder that are rich in magnesium(herein referred to used magnesium oxide), it can cause resource waste and environmental damage if it is not recycled. Using magnesia as raw material, after acid dissolution, removing impurity, employ ammonia water as precipitator to prepare magnesium hydroxide and magnesium oxide. To explore the difference of material reaction ratio, hydrothermal temperature and hydrothermal time on the influence of recovery rate, particle size, and specific surface area of the product. Study found that:by controlling the material ratio and hydrothermal reaction conditions, we can prepare flake-like magnesium hydroxide which middle particle size(D50) is lower than 1μm and small spherical magnesium oxide. Of which, the smallest D50 is only 0.51 μm, the specific surface area is 4.93 m2/g, the recovery rate is as high as 98.44%, and the crystal structure of the product is stable, with less impurity.