Hebei Meixi Biotechnology said that there are three main types of brine: one is the brine by-product after seawater salting, bromine extraction, and potassium extraction;The second is the concentrated brine after salt and potassium extraction from the salt lake;The third is underground brine, which is an aqueous solution with magnesium chloride as the main substance, sometimes containing a certain amount of magnesium sulfate. In some places with sepiolite mines and serpentine mines, the soluble magnesium salts produced by the deep processing of these minerals can also be used to precipitate magnesium hydroxide, such as magnesium chloride aqueous solution produced by acid leaching sepiolite to produce fibrous silica gel. After simple purification, the brine is added with precipitant ammonia or lime (calcium oxide or white cloud ash) to produce magnesium hydroxide precipitation, which is filtered and washed to obtain magnesium hydroxide filter cake. When starting to add ammonia or ammonia or lime milk, basic magnesium chloride is first generated, and then it is converted to magnesium hydroxide when ammonia or lime milk is added.
Seawater, brine is an important raw material for the production of magnesium products in the world today, in the actual production process, if the specific conditions are not followed, the magnesium hydroxide generated by the reaction will become a crystalline fine crystal precipitation, difficult to settle, filter and wash, the product purity is low, and the impurity content is high. Therefore, although the principle of producing magnesium hydroxide is simple, it is not a simple process to produce qualified products.
The main reason is that the control of precipitation process conditions has the greatest impact on the subsequent process and operability. If the precipitation process conditions are not appropriate, it will not only bring difficulties to the subsequent process, but also the purity of the product cannot be guaranteed. For example, when the lime method is used for precipitation, the hydration degree of lime, the amount of addition and other factors have a great impact on the purity of the product and the filtration and washing performance. In the brine monoammonia process, the ammonia flux speed and reaction time seriously affect the filtration and washing effect of magnesium hydroxide.
Hebei Meixi Biotechnology said that the process of preparing magnesium hydroxide from brine (seawater)-ammonia (lime) precipitation method is as follows:
First, the concentrated brine is purified, mainly to remove sediment and organic biological remains, and then prepared into dilute brine with a concentration of about 1mol l of MgCl2 and pumped into the precipitatorThe lime is digested, the slag is removed to obtain lime milk, and the neutralization reaction is carried out by pumping into the precipitator to obtain basic magnesium chloride first, and magnesium hydroxide is obtained by continuing to add lime milk. If you want to obtain basic magnesium chloride, you must control the molar ratio of [OH] [Mg2+] to 0 during the reaction5~0.9. The concentration of brine MgCl2 is 15-3.9mol l, reaction temperature 10 50, reaction time 3 60min.
If digested lime, white cloud ash or ammonia gas is used as a precipitant, the concentration of MgCl2 in the brine should not exceed 15mol l (if ammonia is added, the brine concentration should be greater than 2mol l). When using lime as a precipitant, it is necessary to pay attention to the concentration of lime and the amount added should not be too high, otherwise excessive calcium will be brought in and the purity of magnesium hydroxide will be reduced. Be sure to choose burnt-through, well-digested lime or dolomitic ash. After the reaction is complete, the temperature of the system can be appropriately increased and the aging treatment can be kept for a certain period of time to promote the crystallization of magnesium hydroxide to be more perfect or destroy the magnesium hydroxide sol to achieve the purpose of easy filtration.
The aged system enters the plate and frame filter press for solid-liquid separation, or it can be separated using a suction filter, and depending on the use and transportation, the magnesium hydroxide can be made into powder or paste semi-solid. The magnesium hydroxide content in the paste semi-solid is about 40% 50%, which can be directly used as a material for flue gas desulfurization or wastewater treatment.