Process for obtaining potassium chloride (KCI) from carnalite

Abstract

The process for obtaining potassium chloride (KCI) consists of a sequence of unit stages to obtain a commercial grade product, which is a KCI obtained from low grade sources. The process starts with the salts from the potassium carnallite precipitation pits and the tails from the lithium sulfate process. These then pass through a classification and grinding circuit, then a reverse flotation stage for sodium chloride removal, followed by a leaching stage and finally washing and filtering.

Description

[0001] PROCESS FOR OBTAINING POTASSIUM CHLORIDE (KCI) FROM CARNALITE PREVIOUS ARTWORK

[0002] Currently, the traditional process for producing potassium salts involves the production of two potassium salts in ponds: sylvinite (a mixture of NaCl and KCl) and carnallite (KClMgCl2*6H2O). The sylvinite is processed in a muriate of potassium brine plant (MOP plant) to obtain a 95% KCl salt (KClLA1 Ley).

[0003] Potassium carnallites are leached to produce synthetic sylvinite, with a grade of 25-30% KCl, which had to be transported and used as an intermediate product in obtaining potassium nitrate (KNOs) before having commercial value.

[0004] Document ES 463689 from 1976 describes a process for producing potassium chloride and magnesium chloride hexahydrate from carnallite, and for mixing these chlorides with some balite (sodium chloride). The process involves heating carnallite above 167.5 °C under conditions that prevent water evaporation, to obtain a suspension of potassium chloride in a brine solution containing Mg ions. ++ K + and Cl _ The separation of solid potassium chloride from the aforementioned brine solution. Although this process uses carnallite as a source of KCl, the solution of the invention is carried out at room temperature using flotation to purify and subsequently the reaction of water with the carnallite to obtain the KCl.

[0005] WO2055063625 describes a process for the simultaneous recovery of KCl and KCl-enriched edible salt comprising: (i) desulfation of bitters with CaCl2; (ii) subjecting desulfated bitter water to evaporation; (iii) mixing desulfated bitters from step (ii) with concentrated MgCl2 solution to obtain carnallite; (iv) decomposing carnallite with water to obtain KCl and residual bitters; (v) concentrating the residual bitters to obtain NaCl and KCl in bitters as raw carnallite and decomposed carnallite liquor; (vi) decomposing the raw carnallite from step (v) with water to produce KCl-enriched low-sodium salt, as well as decomposed carnallite liquor; (vii) collecting the decomposed carnallite liquor from steps (v) and (vi) and treating it with lime to generate Mg(OH)2 and filtrate containing CaCl2 and KCl; (viii) recycle the filtrate from step (vii) to step (i), while recovering the KCI lost in the decomposed carnallite liquor;(ix) recycle the final bittering from step (iii) for the production of carnallite and CaCl2; (x) use the excess MgCl2 to recover bromine and obtain MgCl2.6H2O.;

[0006] As in the previous document, a process, albeit a different one, for the production of KCl from carnallite can be observed. However, it does not mention whether the carnallite is a byproduct of a lithium extraction process in any way. Furthermore, it includes a specific step for the separation of NaCl, which is mixed into the obtained KCl. Document US2005 / 0189516 describes a process for producing high-purity lithium from lithium-containing brines. This process involves reducing the amount of magnesium in a lithium-containing brine by adding an aqueous solution of KCl to the brine to precipitate at least some of the magnesium as carnallite salt. Lithium salts prepared using this magnesium removal process are also described.It comprises the amount of magnesium in a brine containing lithium and is adjusted to a lithium content of 4.5 to 6.9% by weight; adding a sufficient amount of a KCl solution to the adjusted brine to precipitate the magnesium as carnallite, and further concentrating the brine to precipitate additional magnesium as additional carnallite.

[0007] Although this document mentions the generation of carnallite as a result of lithium purification, it does not mention that KCl is recovered or produced from the carnallite precipitated in the lithium purification process.

[0008] Document WO2021231597 (equivalent to Chilean patent application 202102989) describes systems and processes that use solar evaporation to pre-concentrate lithium-containing brines to or near lithium saturation, followed by a separation process to separate the lithium from impurities. A separated impurity stream is recycled to a point in the evaporation sequence where conditions are favorable for its precipitation and removal, or it is disposed of in a separate evaporation pond or reinjected underground. Meanwhile, a lower impurity stream is transferred to one or more removal locations, to a later pond in the sequence, or to a lithium plant or concentration facility. Further lithium concentration by evaporation can then take place because the impurities are removed, thus eliminating lithium losses due to co-precipitation and achieving significantly higher lithium concentrations.

[0009] The process includes a sequence of two or more solar evaporation ponds configured to allow brine evaporation to occur in each pond and for the brine to flow from a first pond to one or more ponds in the sequence; a conduit configured to remove at least some of the brine at a brine disposal location and to convey the removed brine to a separator by which one or more impurities are separated from the lithium to form a high-impurity stream and a low-impurity stream;wherein the high-impurity stream is optionally recycled to the evaporation pond sequence at a similar location upstream of the brine extraction site, or disposed of in a separate pond, or reinjected underground, and the low-impurity stream is fed to one or more of the brine removal locations, to a later pond in the sequence, or to a lithium concentration plant or facility; and the brine extraction site is located such that the coprecipitation of lithium together with one or more impurities is reduced compared to the amount of lithium coprecipitation that would occur in the upstream or downstream ponds in the absence of the separation system; wherein the loss of lithium due to coprecipitation is reduced or eliminated.

[0010] The feed to the first pond in the pond sequence is a Chilean-type brine. The stream with a high impurity content is recycled to a pond by precipitating a selected salt from the group consisting of bischofite, calcium borate, anhydrite, gypsum and carnallite or others.

[0011] This document describes the precipitation of carnallite as an impurity when concentrating lithium-containing brines. However, it does not mention that carnallite is treated for the production of potassium chloride (KCl).

[0012] The proposed process substantially improves traditional processes, especially those where KCl has low grade, and takes advantage of lithium sulfate production tailings, where through a sequence of unit steps a commercial quality product is obtained.

[0013] BRIEF DESCRIPTION OF THE FIGURES

[0014] Figure 1: represents a flow diagram of the process for obtaining low-grade KCI from carnallite and lithium sulfate tailings.

[0015] Figure 2: corresponds to a graph showing the impact of the Na law on the equivalent KCl law in the product for a current %Mg. DESCRIPTION OF THE INVENTION

[0016] The process for obtaining potassium chloride (KCl) from carnallite comprises a first stage in which salts from the potassium carnallite precipitation ponds (KClMgCl2*6H2O) and the tailings from the lithium sulfate process (Li2SO4*H2O) are fed into a classification and grinding circuit. After the classification and grinding stage, the resulting product undergoes a reverse flotation stage in which sodium chloride (NaCl) is removed. Following the reverse flotation stage, a leaching stage is performed, and the stream is then subjected to a washing and filtration stage.

[0017] The classification and grinding stage aims to reduce the material size and release the NaCl from the potassium carnallite present in the salts that will subsequently feed the reverse flotation process. Therefore, it includes a sub-stage of crushing, grinding, and regrinding to treat the coarse material. The fines, meanwhile, feed directly to the reverse flotation stage.

[0018] After the classification and grinding stage, the fines are transferred to a reverse flotation stage to extract the sodium from the salt mixture. This process removes the sodium chloride (NaCl) from the final product. Once the sodium chloride is separated from the salt mixture, the now concentrated potassium carnallite is leached with water to dissolve the magnesium, resulting in the chemical conversion to potassium chloride.

[0019] After leaching, the salts are filtered and washed in a belt filter, where the remaining impregnated magnesium is displaced by the wash water. This filter produces a product with 7 to 10% moisture.

[0020] In tests conducted, the results obtained at an industrial scale, considering campaigns up to the present day, yielded a cluster of feed chemicals and the resulting product. The range of data obtained in both the industrial test and subsequent campaigns is presented below.

[0021]

[0022] Table 1. Feed and product obtained in industrial test, section 1.

[0023]

[0024] Table 2. Feed and product obtained in the first campaign.

[0025]

[0026] Table 3. Feed and product obtained in campaign 2.

[0027] The first campaign involving interconnection with the lithium sulfate process tailings began in 2022. These tailings are rich in potassium, low in calcium, and, being a pre-treated stream, have a more homogeneous chemistry and a smaller particle size. The following tables show the feed, interconnection, and product chemistry for the 2022 and 2023 campaigns.

[0028]

[0029] Table 4. Fresh feed, interconnection and product obtained in the 2022 campaign.

[0030]

[0031] Table 5. Fresh feed, interconnection and product obtained during the 2023 campaign.

[0032] The sodium (balite) that was not removed during flotation concentrates in the final product as an impurity due to its lower solubility compared to carnallite in the presence of water. This is shown in Figure 2 during the industrial trial. To obtain a KCl product above 70%, the sodium content in the product cannot exceed 10%. This behavior persisted in subsequent campaigns.

Claims

RECLIN DICATION IS 1. Process for obtaining potassium chloride (KCl) from carnallite, applied to brines where KCl is of low grade, and which takes advantage of the tailings from lithium sulfate production processes, CHARACTERIZED in that it comprises the following stages: a. feed salts from the potassium carnallite precipitation ponds and the lithium sulfate process tailings; b. subject the potassium carnallite together with the lithium sulfate tailings to a stage in a classification and grinding circuit; c. after the classification and grinding stage is completed, the resulting product is subjected to a reverse flotation stage in which the sodium chloride (NaCl) is removed; d. Once the reverse flotation stage is complete, subject the resulting stream to a leaching stage; and e. perform a washing and filtering stage of the stream coming from the leaching stage.

2. Process for obtaining potassium chloride (KCl) from carnallite according to claim 1, CHARACTERIZED in that it comprises, in the classification and grinding stage, releasing sodium chloride from the potassium carnallite to favor the reverse flotation stage.

3. Process for obtaining potassium chloride (KCl) from carnallite according to claim 1, CHARACTERIZED in that the reverse flotation stage comprises extracting sodium from the salt mixture, removing the balite from the final product, concentrating the potassium carnallite.

4. Process for obtaining potassium chloride (KCl) from carnallite according to claim 1, CHARACTERIZED in that the leaching stage is carried out with water, where a chemical conversion of potassium carnallite to potassium chloride is effected, due to the dissolution of magnesium.

5. Process for obtaining potassium chloride (KCl) from carnallite according to claim 1, CHARACTERIZED in that the filtering and washing stage is carried out in a filter belt until reaching 7-10% moisture.

6. Process for obtaining potassium chloride (KCl) from carnallite according to claim 5, CHARACTERIZED in that the filtration and washing stage comprises a washing sub-stage, in which washing water is injected in order to remove the remaining impregnated magnesium.

7. Process for obtaining potassium chloride (KCl) from carnallite according to claim 1, CHARACTERIZED in that the classification and grinding stage comprises a sub-stage of crushing, grinding and subsequent regrinding to treat the flow of coarse material that is fed to the process.

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