| Magnesium carbonate hydrate crystal was selected as target precipitate in extraction of magnesium from brine due to its good filtration properties and excellent dewatering characteristics. In this work, CO2 and MgCl2 were used as raw materials to prepare magnesium carbonates via a novel homogeneous crystal reaction process. This paper adopts a new technology to preparation good filtering performance magnesium carbonate hydrate crystal with brine as raw materials by carbonization under normal pressure. First of all. using magnesium chloride as raw materials, passing carbon dioxide gas into the solution and adding sodium hydroxide into the solution at the same time, regulating pH of the system, explored the reaction temperature, reactant concentration, the system of sodium hydroxide dropping rate, the speed and access time of carbon dioxide, stirring velocity and aging time and other factors on the reaction. The conclusion obtained was applied to simulation the brine, explored the effects of the presence of sodium chloride on the reaction, and analyzed the volume increasing rule in the reaction process. Finally, using bittern as raw material, prepared magnesium carbonate hydrate crystal with good filtering performance.The morphology the filtering performance, particle size, structure and other aspects of products are analyzed by using X ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analyzer. By using the thylenediaminetetraacetic acid disodium salt to determination of magnesium ion concentration in solution, to calculate the purity and yield of the products and reaction speed was analyzed at the same time. Finally, the reaction conditions on the process in different systems were determined and the change rules of products are obtained by analyzing the experimental conditions to preparation excellent products.In the magnesium chloride reaction system. 100mL volume of magnesium chloride was used to carry out the experiments. After testing, we found that temperature had no significant effect on the product filtration performance. However when the reaction temperature is lower than 40℃, the product is acicular magnesium carbonate trihydrate crystal, and when the temperature is higher than 40 ℃, the crystal converted into flake magnesium carbonate. With the decrease of the initial concentration, the filtration of the products performed well, the reaction rate slowed down, crystal surface tends to be smooth, and the yield and purity of the products increased first and then decreased. The slower sodium hydroxide solution droplet acceleration was, the better the performance of the filtration of the products were. And the yield and the purity is higher, the crystal morphology is better. When the carbon dioxide gas pre pass time was 2min, flow rate is higher than that of 1.2L/h, the filtration of the products perform well and the crystal morphology would be perfect. The stirring should be run through the whole process not too fast or too slowly. With the time of aging increase, the crystal size tends to be uniform, and the morphology tends to be ideal.Preparation of magnesium chloride and sodium chloride solution according to a certain proportion as simulation of brine systems to analysis of the effect of the presence of sodium chloride on the yield and product performance of filtration and particle size. Improve the reaction efficiency by improving the concentration of reaction solution and sodium hydroxide solution droplet acceleration in the relatively high temperature. Explore the influence on the system. A preliminary analysis of the reaction was made to get the variation of experimental conditions with the volume increased. The experiment found that the filtering performance and experimental yields of products were not affected by the presence of sodium chloride. At high temperature, the particle size increased with the increasing concentration of sodium chloride. In the high temperature and high concentration, the obtained product filtering performance is not better than low concentration compared with the product, but has been greatly improved. And with the increase of temperature, the filtering performance has a good trend, but the morphology of the product is not the ideal sheet structure. Sodium hydroxide solution under high temperature and high adding speed, the improvement of the filtration performance is not obvious. Amplification experiments by volume 200mL-500mL-1000mL process, the experiment found that proportional amplification method thought is more appropriate the process, the main factors to influence the reaction results are the concentration of reactants.There are large amounts of heavy metal ions in the brine. In order to prevent the influence to the purity of the product and filtration performance, the refined is needed before using. With the simple operation and better effect, neutralization precipitation method is used in the experiment. The alkali is added to the solution for neutralization reaction to make heavy metal ion form water insoluble hydroxide precipitation. Filtrated and separated and the brine would be refined.After the brine refined, the magnesium ion concentration in the brine should be determined by complex ometric titration. According to reaction conditions have been got by the reaction of magnesium carbonate, prepare products under normal temperature and pressure. The magnesium carbonate trihydrate crystal produced, filter performing well, the crystal morphology is acicular, surface is smooth, and the size is uniform. However, with the increase of the volume, reaction yield decreased. |
