Hebei Messi Biology Co., Ltd Tibet Nagqu Bango Lake water magnesite (4MgCO3-Mg(OH)2-4H2O) is a natural alkali carbonate mineral with rich reserves, its texture is pure, white color, low impurity content, is a high quality mineral raw material for preparing magnesium products such as flame retardant, active magnesium oxide, heavy alkali magnesium carbonate, nano magnesium hydroxide. However, due to the geographical, traffic and technical factors, it restricts its development and utilization, and there are few related researches in China. Therefore, how to develop and utilize magnesite to prepare a series of high quality magnesium compounds is the main research and development work at present. Therefore, Hebei Messi Biology Co., Ltd. is dedicated to develop green, low cost and suitable for industrial production of high quality magnesium oxide and nano-magnesium hydroxide by using hydromagnesite as raw material.
Messi Biology used hydromagnesite as raw material, using the process route of \”calcination-hydration-calcination\” to prepare magnesium oxide nanoparticles with different characteristics, and the experimental process without adding any other reagents. The influence of calcination conditions on the morphology, crystallinity, grain size and specific surface area of the samples was investigated, and the results showed that the increase of temperature or calcination time helped to improve the crystallinity of magnesium oxide, promote the crystal growth and reduce the specific surface area. The experiments finally concluded that:calcination at 650 ℃ for 1h could obtain mesoporous mesh-like magnesium oxide with specific surface area up to 188.3m/g; calcination at 850 ℃ for 4h could obtain rod-like and dumbbell-like magnesium oxide nanoparticles.
The results showed that the repeated hydration step could improve the crystallinity of the magnesium hydroxide sample and promote the grain growth, and the calcined magnesium oxide could maintain the structure of the precursor. The experiments finally concluded that: the second hydration can obtain the magnesium hydroxide nanosheets with hexagonal shape, and calcination at 650℃ for 1h can obtain the flaky magnesium oxide nanosheets; calcination at 850℃ for 1h can obtain the flaky mesoporous magnesium oxide nanosheets.
Then Hebei Messi Biology Co., Ltd. used hydromagnesite as raw material, and determined that the process route of \”calcination-hydration-calcination-hydrothermal\” can produce regular hexagonal flakes with high dispersion of magnesium hydroxide. The hydrothermal conditions were investigated, and the results showed that the control of hydrothermal conditions could change the crystal growth direction during the hydrothermal process, so that the exposure of 001 crystalline surface with weak polarity increased and the exposure of 101 crystalline surface with large polarity decreased. The experiments finally determined the amount of magnesium oxide:25%, hydrothermal temperature:150℃ and hydrothermal time:3h as the best hydrothermal conditions. The modification conditions were experimentally explored, and the results showed that the growth direction of magnesium hydroxide tended to be consistent and the dispersion was effectively improved under the condition of 4% PVP. Finally, the magnesium hydroxide nanoparticles with the average diameter of 300nm~400nm, thickness of hexagonal sheet of 40nm~60nm, regular crystal shape and good dispersion were obtained.
Finally, the removal ability of heavy metal ions by mesoporous mesh magnesium oxide with high specific surface area prepared from hydromagnesite was explored by Hebei Messi Biology Co. Take the adsorption of lead as an example, the effect of adsorbent dosage, adsorption time, temperature and pH on its adsorption performance was investigated, and the best adsorption conditions were obtained when the adsorbent dosage was 0.05g/L, the adsorption time was 45min, the solution was pH between 6-8 and the adsorption temperature was room temperature, and the removal rate of lead ions could reach more than 99.8% at this time. The adsorption kinetics and isotherm data of lead adsorption by this MgO adsorbent were in high agreement with the pseudo-secondary model and Langmuir model, indicating monolayer chemisorption of heavy metal ions with a maximum adsorption capacity of 7431.5 mg/g, which is the highest value reported so far based on MgO adsorbent. An adsorption mechanism involving hydroxyl functional groups and ion exchange between magnesium and heavy metal ions on the magnesium oxide surface was proposed. In addition, this magnesium oxide can adsorb a variety of ions simultaneously, with excellent adsorption properties for cadmium, chromium, nickel, arsenic, cobalt, lead, selenium, beryllium, bismuth, copper, iron, manganese, vanadium, zinc and aluminum ions.
The above results show that the magnesium oxide adsorbent has the advantages of high efficiency, low cost, easy preparation and easy promotion, and is harmless to the environment, which is expected to be an excellent adsorbent for rapid removal of heavy metal ions in wastewater.