Chemical process for the treatment of carnallite-type potash ore (KCl.MgCl2.6H2O) associated with halite (NaCl)

Abstract

The invention concerns a process for extracting high-purity potassium chloride (KCl) from carnallite ore (KCl.MgCl2.6H2O) associated with halite (NaCl). It begins with a selective dissolution, prioritizing KCl and MgCl2, due to the addition of water at room temperature. Two basification steps follow, involving the addition of potassium hydroxide (KOH) to the solution obtained after the dissolution of the ore. The first addition allows the extraction of all Mg2+ ions in the form of magnesium hydroxide (Mg(OH)2), a valuable product. The second addition of KOH aims to convert all the NaCl into potassium chloride (KCl) and sodium hydroxide (NaOH). This second addition of KOH is excessive to promote the formation of the desired products during the two crystallization steps that follow. After the chemical transformations of the mineral solution, a concentration step is undertaken to vaporize the water, thus promoting the crystallization of potassium chloride (KCl). A second concentration is followed by cooling to form solid sodium hydroxide (NaOH). The water vapors generated during the two concentration steps are liquefied by cooling for recycling. The three solid products resulting from the process undergo drying to remove moisture, thus meeting market requirements in terms of purity. The proposed process is distinguished by zero waste management and low water consumption, with more than 90% of water recycled initially, as well as KOH recycling at the end of the process. In addition, it requires little energy, as KOH dissolution is exothermic. The KCl production of this process is high thanks to the regeneration of KCl during chemical transformations, and it is characterized by its flexibility in dealing with different compositions of the starting ore.