| China has abundant brine resources, such as salt brine, underground brine, salt lake brine. However, the low utilization rate causes great waste of liquid resources of magnesium. Take salt brine for example, the great amount of brine produced after salt production is poured into sea or rivers directly, therefore, in one hand, it causes serious waste of resources, on the other hand, the Mg2+ions in brine could affect water quality. Hence, it is an important issue about how to develop the magnesium resources effectively.Recently, the series of magnesium compounds has many outstanding properties, such as, light weight, nontoxic, etc., all of which are advantageous for their use in many areas such as electronic industry, aerospace, pharmaceutics, etc.Currently, Polymer Materials such as rubber and plastics have been widely used. It is one of the fastest growing applied materials. However, the important defect of this materials is inflammable. The best way to avoid fire disaster is to add flame retardants in them.Magnesium hydroxide has attract much attention as a popular, green flame retardant, because its ability of undergo endothermic dehydration when materials are on fire. Magnesium hydroxide does not produce toxic and corrosive gas in fire conditions. Besides, Magnesium hydroxide starts to decompose at330℃. It absorbs much energy during combustion, and its associated endotherm is as high as1450J/g, which matches for almost of all polymeric materials. Besides, Magnesium hydroxide can also be neutralizer to treat with acidic waste, as fertilizer additive, as antacids in pharmaceutics, and the primary precursor for MgO.There are many methods to prepare Magnesium hydroxide such as precipitation, hydrothermal method, sol-gel method, electrodeposition method, solvothermal method, Microwave-assisted synthesis, etc. Direct precipitation is the most convenient and the commonly used way to prepare magnesium hydroxide.In this paper, brine and different alkali solutions are used as materials. This is an example to use brine. This work proves that brine is a fine liquid magnesium resource.1. brine-ammonia method to prepare flower-like magnesium hydroxideWith brine and ammonia as raw materials, magnesium hydroxide was prepared by controlling the mole ratio of MgCl2/NH3·H2O, the mass fraction of ammonia, reaction temperature, aging time. These factors were discussed how to effect the purity and yield of magnesium hydroxide. The products were characterized by XRD and SEM. The XRD patterns showed that when the reaction temperature was60℃, the products had high crystallinity. It turned out the morphology of products were amorphous flake. When the temperature increased to80℃, the morphology changed to flower-like magnesium hydroxide.2. Brine-Sodium hydroxide method to prepare hexagonal lamellar plates of Mg(OH)2with uniform size, high dispersion, low polarity.As we can see form the first experiment, the products prepared by direct precipitation was not well dispersive, so a new way to prepare Mg(OH)2by a two-step process was adopted. First, Mg(OH)2precursor was precipitated at room temperature, then the precursor was hydrothermally treated. The results indicated that the particle size, the shape of the products and the crystallinity were affected by the temperature and the time of the hydrothermal reaction. We found that when the products were under treatment at170℃for9hours, hexagonal lamellar was obtained. The nano-lamerllar plates are very good candidates for polymeric materials as flame retardants.3. The surface modification treatmentThe effect of the modification was studied by means of oil absorption and settling volume. It turns out the oil absorption of products prepared under hydrothermal treatment is much lower than the products prepared without hydrothermal treatment. In other words, the oil absorption of regular lamellar plates is much lower than that of amorphous flakes. Three kinds of modifier were used in this research:A172, low-hydro silicone oil and triphenylsilanol. The results showed the oil absorption of products modified by A172decreased not significantly. So we turned to the second modifier low-hydro silicone oil, the products modified were not well dispersed in paraffin. But it showed good dispersion after modified by triphenylsilanol. We also found out that hydrothermal treatment in alkaline solution was a good way to reduce the mount of oil absorption. Hence, we added a certain amount of sodium hydroxide before hydrothermal treatment, then products were modified by triphenylsilanol. The results revealed that the products modified this way had the lowest oil absorption and the settling volume is high, the settling rate slowed significantly. |
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