Separation of Magnesium and Lithium from Brine Water and Bittern Using Sodium Silicate Precipitation Agent

1. Introduction

The development of lithium batteries for electric vehicles shows a bright prospect for the future. It is related to the higher demand for environmentally friendly transportation technology. As the need for lithium batteries for electric vehicles grows, the consumption of lithium carbonate will increase. Lithium carbonate consumption in 2011 was mainly concentrated in ceramics and glass, with a percentage of 29%, and lithium batteries at 27% [ 1 ]. In 2015 the consumption of lithium carbonate shifted to 35% for lithium batteries [ 2 ]. World lithium production has increased by 6% annually from 2010 to 2017. In 2017, world lithium production was 43,000 metric tons, and it is predicted that in 2025 it will reach 95,000 metric tons [ 3 ].

The natural resources of lithium in the world come from two main sources: primary materials derived from natural resources and secondary materials derived from used battery waste and mining waste slag. Primary materials from natural resources come from extracting lithium from granitic rocks, spodumene, and lithium salts from brine water [ 4 ]. In 2018 the world’s lithium production was around 43,000 metric tons, of which 55% came from brine water. Some lithium carbonate producers from brine water are Chile (32.8%) and Argentina (12.8%), while lithium from rocks comes from Australia (43.5%) and Zimbabwe (2.3%) [ 5 ]. Australia dominated the world’s lithium production before 2015 with a capacity of 15.8 kt Li/Year from rock production. After 2015 Australia’s lithium production declined because it could not compete with lithium production from brine water from South America [ 6 ].

The main problem in producing lithium carbonate from brine water is the low content of lithium ions and high levels of magnesium ions. The magnesium and lithium ions in brine water are present in chloride, sulfate, or carbonate anions solutions. The separation process of magnesium ions and lithium ions in brine water is the key to successfully extracting lithium from brine water which is indicated by a small Mg/Li ratio. The smaller the ratio of Mg/Li in brine, the better the separation of Mg ions and Li ions so that brine water is free from Mg ions which can be used as raw material in the manufacture of high purity lithium carbonate [ 7 ]. Currently, the largest global lithium producer from brine water is in Atacama, Chile, with a magnesium ion level of 9600 ppm and lithium ion of 2100 ppm, with an Mg/Li ratio of 6.4 [ 8 ].

Various research activities have been carried out to separate magnesium and lithium from brine water to obtain brine water with a low magnesium content. The process of separating magnesium ions in brine water includes permeation using membrane [ 3 ], precipitation [ 7 ] and electrolysis [ 8 ]. The precipitation process is the simplest separation process because it does not require expensive chemicals or complicated equipment. Generally, the chemical reagents used for precipitation processes are based on aluminum [ 9 10 ], oxalic acid [ 11 12 ], ammonium phosphate [ 13 ], and sodium metasilicate [ 14 ]. Hai (2018) used sodium silicate to separate lithium and magnesium [ 15 ]. The process was carried out by reacting sodium silicate crystals with brine water vapor at a temperature of 180 °C. The precipitation product was hectorite, which can be directly applied as a lithium-based catalyst [ 15 ].

The potential of natural lithium resources in Indonesia, which comes from brine water, has not yet been used commercially, even though Indonesia is located in the Ring of Fire zone [ 16 ]. In the Ring of the Fire zone, the geothermal sources’ intrusion process brings brine water into the earth’s surface in the form of hot mud sources [ 16 ]. One source of Indonesian brine water that has the potential to be developed is Bledug Kuwu which has a lithium content of 138.64 ppm and magnesium 690.62, with an Mg/Li ratio of 4.99 [ 12 ]. To extract lithium from Indonesian brine water, the brine water must undergo an evaporation process to increase the lithium content and the magnesium separation process.

4 Na2SiO3 + 3 MgCl2 + 2 HCl + m H2O → Si4Mg3O11·n H2O + 8 NaCl + (m−n) H2O

(1)

In this study, magnesium and lithium were separated by precipitation of magnesium ions in brine water and bittern with sodium silicate solution. In the deposition process, a white precipitate of magnesium silicate is formed, which can be separated from the filtrate. The filtrate should be free of magnesium, and lithium not precipitated together with magnesium. The reaction of precipitation of magnesium ions with sodium silicate is as follows (Equation (1)) [ 17 ]:

2 CaCl2 + Na2SiO3 + H2O → 2 CaO·SiO2 + 2 NaCl + 2 HCl

(2)

Generally, in brine water, besides magnesium, there is also an element of calcium that can react with sodium silicate to form calcium silicate deposits. The reaction for the formation of calcium silicate generally forms 2CaO.SiO, the reaction is shown as follows (Equation (2)) [ 18 ]:

Several parameters need to be investigated regarding the effect of the evaporation process in separating magnesium from brine water to produce lithium-rich brine water. Therefore, in this study, we observed the performance of the magnesium ion precipitation process by sodium silicate to separate magnesium in brine water. Brine water in this study had different initial treatments, namely, brine water without the evaporation process and brine water concentrate (bittern) resulting from the evaporation process. Extraction of lithium from brine water commercially starts with increasing the concentration through evaporation by sunlight for 18–24 weeks. The result of the evaporation process in the form of brine water concentrate is then separated from the magnesium ions using a calcium carbonate precipitation process. Then the magnesium-free lithium concentrate is precipitated by the sodium carbonate precipitation process [ 19 ].

This study aims to investigate the precipitation of magnesium from brine water and bittern using sodium silicate as a precipitating agent with the presence of other ions. It also compares the selectivity of magnesium and lithium ions between brine water and bittern.