Lithium recovery from borax dilute solutions

Abstract

An improved method of lithium recovery from borax dilute solution is provided. In this method, boron in the borax dilute solution is removed from the medium as borax decahydrate and while this removal process is carried out, liquid-liquid extraction with organic sedimentary chemicals or ion exchange resins are not used.

Claims

1. A method of recovering lithium from a borax dilute solution, comprising the following steps: reducing the solution containing 200-400 ppm Li.sup.+(dilute solution) to 20-50% of its initial volume by evaporation, filtering the concentrate solution obtained as a result of evaporation and removing the borax decahydrate from a medium by cooling down to below 25° C., after the borax decahydrate is removed from the medium, filtering the impurities in the medium by bringing the pH value of the solution to 10.5-12 level, reheating the solution, from which boron and impurities have been removed to obtain a turbid solution, then filtering the turbid solution, then obtaining lithium carbonate (Li.sub.2CO.sub.3) with a purity of about 70% by reducing it to 4-8% of its initial volume by evaporating the solution for the 2nd time, obtaining Li.sub.2CO.sub.3 with a purity over 99% by dissolving in deionized water (alternatively, alcohol) at a temperature over 90° C., precipitating lithium phosphate (Li.sub.3PO.sub.4) by adding a phosphate source to the medium at a temperature above 80° C. for recovering the lithium remaining in the solution.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) According to the invention, the method of lithium recovery from borax dilute solutions comprises reducing the solution containing 200-400 ppm Li.sup.+ (dilute solution) to 20-50% of its initial volume by evaporation, filtering the concentrate solution obtained as a result of evaporation and removing the borax decahydrate from the medium by cooling down to below 25° C., after the borax decahydrate is removed from the medium, filtering the impurities in the medium by bringing the pH value of the solution to 10.5-12 level, filtering the turbidity containing impurities that is obtained by reheating the solution, from which large amounts of boron and impurities have been removed, then obtaining lithium carbonate (Li.sub.2CO.sub.3) with a purity of about 70% by reducing it to 4-8% of its initial volume by evaporating the solution for the 2nd time, obtaining Li.sub.2CO.sub.3 with a purity over 99% by using deionized water (alternatively, alcohol) over 90° C., precipitating lithium phosphate (Li.sub.3PO.sub.4) by adding phosphate source (sodium phosphate dodecahydrate (Na.sub.3PO.sub.4.12H.sub.2O)) to the medium for recovering a significant amount of lithium remaining in the solution, synthesis of lithium phosphate (Li.sub.3PO.sub.4) with a minimum purity of 70% precipitated at a temperature above 80° C.

(2) The dilute solution used in the method of the invention contains lithium as well as borax. The efficiency will be increased by incorporating the dilute solution to the production of borax decahydrate by taking the borax decahydrate in this solution and keep it in the dams. In addition, a study was carried out to meet the industrial lithium demands with domestic resources by synthesizing lithium chemicals. The lithium compounds to be produced as a result of this study will be usable in all sectors where lithium is used. Further, the amount of water consumed in factory productions where groundwater is used will decrease considerably with the anticipated evaporation and feedback to the system. This is an economical and environmentally friendly approach.

(3) When the production methods of lithium compounds are examined around the world, it is seen that production is made from salt water (brine) or mineral resources such as spodumene. However, when the production methods are examined in detail for economical reasons, brine comes into prominence and is used as raw material in almost all of the production of lithium compounds. The concentration of lithium therein is increased by naturally subjecting the brine to evaporation.

(4) To produce lithium carbonate, the lithium is converted from the chloride form to the carbonate form by adding soda ash (Na.sub.2CO.sub.3). In the method known as the traditional method, the recovery of lithium is around 50%. The production process varies between 8-36 months depending on weather conditions. For this reason, there are bottlenecks in sudden demand increases.

(5) In addition, when the current production processes are examined, no production is observed with the solution with high boron content as we use in our studies. In the said production processes, organic solvents are used to obtain the boron from the medium and boric acid synthesis is carried out as the final product. In the method of the invention, while lithium is obtained, the boron in the medium is removed from the medium as borax decahydrate.

(6) TABLE-US-00001 TABLE 1 The content of the dilute solution used in the method of the invention Li.sup.+ K.sup.+ Mg.sup.+2 Ca.sup.+2 SO.sub.4.sup.−2 B Na.sup.+ (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) (g/L) Mg/Li SO.sub.4/Li Ca/Li B/Li Dilute 200-400 200-1200 10-800 25-150 1.4-3.5 2.9-46.6 4.4-60 0-4 3.5-17.5 0-0.4 7.3-233 Solution

(7) The ratios of Mg/Li and Ca/Li should be low in the production using the traditional method. As these rates increase, the chemical cost required for removing calcium (Ca), lithium (Li) and magnesium (Mg) from the medium increases and the economics of the process disappears. Also, the increase of the ratio of SO.sub.4/Li causes the lithium to be removed from the medium as sulphate salts during the formation of lithium concentrated solution and decreases the lithium recovery efficiency. Therefore, it may be necessary to remove the sulphates in the medium before the lithium compounds are obtained.

(8) In view of the drawbacks of the traditional methods, it is desired to produce lithium from the borax dilute solution in the method of the invention.

(9) When calcium chloride (CaCl.sub.2) or calcium hydroxide (Ca(OH).sub.2) is used for sulphate (SO.sub.4) removal as in traditional methods, economically valuable sodium borates, which are high in the medium, can be converted into less valuable calcium-containing borates.

(10) Lime and soda ash used in the traditional method of removing Mg and Ca from the medium will form less valuable borates with calcium and magnesium content in the borax dilute solution.

(11) If the high boron content in the borax dilute solution is taken with organic solvents as in traditional methods, both the costs will increase and the risk of organic impurities contaminating the borax production process will occur.

(12) With the method of the invention, lithium compounds needed by the industry can be synthesized from domestic sources. In addition to this, boron and water in the solution that are surplus in factories will be returned to the system. With the proposed method, the recovery of lithium can be increased from the 50% level in the traditional method of precipitation to over 85%. Unlike the current methods, sodium borate compounds are also produced in addition to lithium production instead of boric acid.

(13) Accordingly;

(14) Within the scope of this invention, the borax dilute solution is reduced to 20-50% of its initial volume, and is filtered and cooled down to below 25° C. The ratio of 20-50% of the initial volume is important, because the lithium in the medium should not dragged with boron during crystallization. Thus, the borax decahydrate therein is removed from the medium and the buffer effect of the borax in the medium is gradually reduced.

(15) After the borax is removed from the medium, the impurities in the medium are removed by bringing pH value of the solution to 10.5-12 level. Here, the absence of filtration prevents core crystallization of borax in the form of the decahydrate and its precipitation. The high boron content that will be present in the medium due to the non-precipitated decahydrate also prevents crystal nucleation of lithium carbonate, and thus, lithium carbonate cannot be produced.

(16) It has been found that there is no need to add any chemical to the medium when the pH value is within the specified range above. The reason for this is the effect of sodium carbonate in solution, which is used in our borax production process, on pH. When adjusting the pH, if necessary, sodium hydroxide (NaOH) or sodium carbonate (Na.sub.2CO.sub.3) can be used. By adjusting the pH, impurities such as calcium (Ca), magnesium (Mg) and strontium (Sr) in the medium can be substantially removed from the medium as solids.

(17) The turbidity containing impurities occurs by reheating the solution, of which large amounts of boron and impurities have been removed, and then the turbid solution is filtered. Then lithium carbonate (Li.sub.2CO.sub.3) is obtained from the filtrate with a purity of about 70% by evaporating the filtrate to 4-8% of its initial volume. If there is more or less evaporation level, the desired lithium recovery rate and lithium carbonate purity cannot be achieved. Following this, Li.sub.2CO.sub.3 is obtained with a purity over 99% by using deionized water (alternatively, alcohol) over 90° C. The final evaporation level determined is such that the sulfates in the medium will not affect the lithium recovery.

(18) In order to remove the lithium carbonate, which remains soluble in solution and does not precipitate, from the medium, re-evaporation cannot be performed due to other components (SO.sub.4, B, Na, CO.sub.3) in the medium. Thus, lithium phosphate (Li.sub.3PO.sub.4) was precipitated by adding phosphate source (Na.sub.3PO.sub.4.12H.sub.2O) to the medium for recovering a significant amount of lithium remaining in the solution. Li.sub.3PO.sub.4 which was precipitated at a temperature above 80° C. has a minimum purity of 70%.

(19) In this context, at least 85% of the initial lithium content is recovered, which is higher than the recovery percentage achieved with conventional methods (about 50%).

(20) To summarize the benefits to be obtained by the method used in this invention: Economically valuable boron in the dilute solution will be recovered. Thus, the efficiency in the borax factories will increase. Unlike the production methods in the world, lithium compounds with high economic value will be synthesized with a method specific to domestic resources so that external dependence will be reduced. For the first time in our country, the production of industrial scale lithium compounds can be carried out within this scope. The storage area of the dilute solution will be reduced, thereby reducing the expenditure on artificial ponds that incur increasing high costs. The water used in factories will be reused so that the damage to the environment due to excessive water usage will be minimized. At least 85% of the lithium content in the dilute solution was removed from the medium as lithium compounds, thus exceeding the rate (50%) in traditional methods.