Available on line at Association of the Chemical Engineers of Serbia AChE Chemical Industry & Chemical Engineering Quarterly www.ache.org.rs/CICEQ Chem. Ind. Chem. Eng. Q. 24 (3) 239−249 (2018) CI&CEQ J.A. TAVARES CRYSTALLIZATION AND SEPARATION OF L.F. MOURA KCl FROM CARNALLITE ORE: PROCESS A. BERNARDO DEVELOPMENT, SIMULATION AND M. GIULIETTI ECONOMIC FEASIBILITY Chemical Engineering Department, Federal University of São Carlos Article Highlights (UFSCar), Rodovia Washington • Evaluation of alternatives for producing KCl from carnallite by crystallization Luiz, São Carlos, SP, Brazil • Process synthesis for KCl production from KCl-MgCl2-H2O system phase diagram with saturated NaCl SCIENTIFIC PAPER • Feasibility evaluation of a KCl crystallization plant considering capital and operating expenses UDC 553.3/.4(81):546.32’131:66 Abstract Given the increasing demand for potassium in Brazil, the mining and use of carnallite is becoming increasingly important, because the current source of potassium, sylvinite, is being depleted and there is a risk of shortages. Based on theoretical and practical data available in existing literature, this work describes the development, simulation, and economic feasibility of a process for dissolution and crystallization of potassium chloride from carnallite ore. Positive results were obtained following the application of the Hoffman diagram and determination of the corresponding equation. The proposed process pro- vided over 85% potassium chloride crystallization, demonstrating its superior performance, compared to existing procedures. Keywords: carnallite, potassium chloride, crystallization, process syn- thesis, economic assessment. Potassium is the seventh most abundant ele- Evaporite deposits are therefore the most important ment on Earth, accounting for around 2.4% of its crust sources of potassium salts, because the salts present by mass. It is only found in the form of compounds, in these deposits are soluble in water and can be due to its high reactivity and association with other mined and processed more easily. The main evapo- elements, with chlorides and sulfates being most rite deposits of potassium that can be highlighted, common, at levels above 10% in many minerals. The together with their K2O equivalents, are as follows: highest contents of potassium are found in evaporite sylvinite (KCl, 63% K2O); carnallite (KCl⋅MgCl2⋅6H2O, minerals and potassium silicates. Although silicates 17% K2O); kainite (KCl⋅MgSO4⋅3H2O, 19.3% K2O); contain between 10 and 20% of K2O equivalent and langbeinite (K2SO4⋅2MgSO4, 22.7% K2O); polialite are abundant on Earth, they do not represent import- (K2SO4⋅MgSO4⋅2CaSO4⋅2H2O, 15.6% K2O); schoenite ant potassium resources because they are not sol- (K2SO4⋅2MgSO4⋅4H2O, 25.7% K2O); singernite uble in water and their chemical bonds are difficult to (K2SO4⋅CaSO4⋅H2O, 28% K2O) [2]. break, making their mineralization impossible [1]. The utilization of potassium as a plant fertilizer dates from ancient times. There are references to its use since the 3rd century BC, when it was obtained Correspondence: A. Bernardo, Chemical Engineering Depart- from the ashes of wood and salting from marine salts, ment, Federal University of São Carlos (UFSCar), Rodovia Wash- ington Luiz, km 235, São Carlos, SP, Brazil. but a process for potassium salt production from car- E-mail: [email protected] nallite for use as fertilizer was only proposed by Frank Paper received: 19 January, 2017 [3]. Potassium is a key mineral nutrient for plants and Paper revised: 24 August, 2017 Paper accepted: 28 September, 2017 animals, and is the third most abundant mineral ele- https://doi.org/10.2298/CICEQ170119036T ment in our bodies, only exceeded by calcium and 239 J.A. TAVARES et al.: CRYSTALLIZATION AND SEPARATION OF KCl… Chem. Ind. Chem. Eng. Q. 24 (3) 239−249 (2018) phosphorus. Over 85% of the potassium in the human of carnallite, which are transferred to a decanter flask, body is found in key organs, and neither animals nor where an elutriator separates the solutions of pot- plants can live without an adequate potassium intake. assium chloride and sodium chloride. The sodium Belarus (57%), Canada (17%) and Russia (10.4%) chloride solution is transferred to a separation flask, are globally the three largest producers of potassium. where the sodium chloride is removed, and a portion Due to the small domestic production, compared to of this solution is then recycled to the decanter. The the country’s large demand for potassium, Brazil is a potassium chloride separated in the decanter is rem- major importer of potassium fertilizer, and in 2013 oved by centrifugation. The remaining potassium imported 7.6 million t of potassium chloride (KCl) from chloride solution is transferred to a cooling flask, in its main suppliers: Canada (31.59%), Germany which the temperature is reduced to 115.7 °C. This (16.46%), Russia (15.63%), Belarus (14.86%) and cooled solution is transferred to another separation Israel (9.43%). Globally, over 95% of the potassium flask, where carnallite and bischofite are separated. produced is used as fertilizer, with 90% in the form of The bischofite is stored and the carnallite is recycled potassium chloride, and the remainder is consumed to the fusion vessel. by chemical industries [4]. The US3642454 patent [7] describes the crys- Brazilian mineral reserves containing potassium, tallization of potassium chloride from carnallite. This measured as K2O, are estimated to be 16 billion t, process begins with the dissolution of carnallite, according to the Brazilian National Department of preferably with fresh water in order to be able to dis- Mineral Production (DNPM) [4], including the reserves solve all the magnesium chloride, which ranges from of carnallite and sylvinite. The Brazilian regions in one to two and a half times the weight of carnallite. which there are proved reserves of potassium are After this stage, the resulting solution and the Sergipe and Amazonas states. In Sergipe, potassium undissolved salts of potassium chloride and sodium reserves are estimated in 14.4 billion t of carnallite chloride are separated. The separated solid salts are and 480 million t of sylvinite, with about 8.31 and dissolved in the next stage, preferably using fresh 10.40% of K2O, respectively. According to Warren [5], water, generating a solution containing sodium chlo- the Sergipe deposit is composed of stacked cycles of ride and potassium chloride, which goes through a halite, carnallite and sylvite up to 800 m thick. More process of solar evaporation to crystallize the salts than 750,000 t/year of potash ore is extracted by Vale with a high level of potassium chloride (between 66 in its conventional Taquari-Vassouras potash mine. and 76% of the crystals). Finally, the crystallized salts The deposit is small, estimated to be 11 million t of are sent for refining by a washing process, which K2O, and the mine has an operating cost of $174 per t increases the purity of the crystals to 95% potassium and a projected productive life of nine years. In Ama- chloride. zonas, mineral reserves containing potassium are Patent US6022080 [8] developed for producing estimated to be 1 billion t of sylvinite containing about potassium chloride (KCl) from carnallite consists in a 18.47% of K2O equivalent. These deposits are in the process in which water is heated in a pond by solar localities of Fazendinha and Arari, in the Nova Olinda energy up to a value between 60 and 80 °C, and is do Norte region, and there is no project for exploiting sequentially introduced into a cavern to solution mine this area [4]. the carnallite layer and produce the brine. This brine The crystallization and separation operations is pumped up to surface and fed in a natural evapor- aimed to obtain the greatest possible amount of the ator coupled to an exhauster (crystallizer) which cools desired salt. In order to achieve this, there are several the solution to a temperature between 30 and 40 °C, processes described in the literature that can be crystallizing sodium chloride (NaCl) and potassium considered. The process of diluting carnallite is the chloride (KCl) as final products. most widely used method, resulting in a solution that Patent US8282898 [9] presents a crystallization is heated to 105 °C in an evaporator and then cooled process for high purity KCl from carnallite. The des- in a crystallizer to produce the potassium chloride cribed steps are the dissolution of carnallite to form a salt. Several patents have been registered for this solution containing NaCl, magnesium chloride and process. KCl. The concentration of MgCl2 must be controlled According to the US4140747 patent [6], the between 12 and 25% weight to avoid co-precipitation production of potassium chloride and magnesium of NaCl. The patent claims that if the NaCl weight chloride from carnallite is achieved by feeding car- concentration is not greater than 2% in solution, KCl nallite into a fusion vessel that is heated to 167.5 °C. crystals will have high purity. This results in a suspension of sylvinite and a solution 240 J.A. TAVARES et al.: CRYSTALLIZATION AND SEPARATION OF KCl… Chem. Ind. Chem. Eng. Q. 24 (3) 239−249 (2018) Due to increasing demand in Brazil, the exploit- and K2Cl2, were read for each curve (dissolution tem- ation of carnallite is essential in order to supply part of perature) in the original diagram. A linear regression the national demand for this alkali metal, since the was performed to describe each of the curves gen- current main natural source, sylvinite, is becoming erated in Origin and MS Excel. With all the equations depleted, leading to a risk of shortages. obtained for each temperature, another linear regres- The current consumption (production + import- sion was performed, generating a general equation ation–exportation) is around 8.1 million t of KCl, and that could effectively describe the entire diagram. this amount minus the production of 0.49 million t of Simulation of the process KCl results in an internal demand deficit of 7.69 million t of KCl, which is indicative of the potential for The simulation was performed in MS Excel, increased domestic potassium production in Brazil [4].