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3.1.2. Alkaline process In the alkaline process (Table 5), spodumene or lepidolite ore concen- trates are ground and calcined with limestone at 825–1050 °C. The resulting calcine is crushed, milled and treated with water to yield lithi- um hydroxide which can be converted to chloride by reaction with hy- drochloric acid. The recovery in this method is approximately 85–90% (Averill and Olson, 1978). The reaction during calcination of spodumene with limestone can be represented as : Li2O⋅Al2O3⋅4SiO2ðsÞ þ CaCO3→Li2OðsÞ þ CaO⋅Al2O3⋅4SiO2ðsÞ þ CO2ðgÞ: ð4Þ Lepidolite was pre-roasted at 860 °C under water steam atmosphere for defluorination followed by pressure leaching of the defluorinated mass in a lime–milk autoclave at 150 °C. In this process 98.9% lithium was extracted (Yan et al., 2012c). During the roasting with steam forma- tion of phases such as lithium aluminium silicate (beta-eucryptite) and leucite (KAlSi2O6) was noticed (Karstetter, 1971) as per reaction (5) 750 °C, ~98% of the lithium contained in spodumene is converted to its chloride which can be water leached (Zelikman et al., 1996). Vyas et al. (1975) reported a similar process using CaCO3 and CaCl2 to roast Indian lepidolite at 950 °C by which 80% Li was recovered as LiCl. The chlorination process with calcium chloride and/or sodium chloride with lepidolite (M = Li, K, Rb, Cs) may be represented as: 2NaCl þ 6SiO2 þ M2O þ Al2O3→2NaAlSi3O8 þ 2MCl ð8Þ CaCl2 þ SiO2 þ M2O→CaSiO3 þ 2MCl ð9Þ CaCl2 þ 2SiO2 þ Al2O3 þ M2O→CaAlSi2O8 þ 2MCl: ð10Þ Chlorination roasting with a mixture of CaCl2 and NaCl gives a better lithium extraction yield because of its lower melting point than either of the agents, which increases the fluidity of chloride melt. This allows diffusion of the chlorinating agent to the surface of the lepidolite facili- tating the lithium extraction selectively and yielding a pure product. Crocker and Lien (1987) also reported a process for selective chlorina- tion of hectorite (0.3–0.65% Li) in clays with limestone at 750 °C using 20 wt.% HCl. 3.1.4. Other processes Chlorination roasting of ores requires corrosion-resistant equip- ment. To overcome this drawback the autoclave method is used. Chen et al. (2011b) reported a process to treat β-spodumene obtained in the calcination of α-spodumene, by sodium carbonate solution in an au- toclave at a liquid/solid ratio of 4 and Na/Li of 1.25 at 225 °C. During pressure leaching lithium carbonate and analcime slurry are formed according to reaction (11). β−Li2O⋅Al2O3⋅4SiO2 þ Na2CO3 þ nH2O→Li2CO3 þ Na2O⋅Al2O3⋅4SiO2⋅nH2O: ð11Þ The slurry was leached in carbon dioxide to form lithium bicarbonate which on heating produced lithium carbonate of 99.6% purity as per reactions (12) and (13). Li2CO3 þ CO2 þ H2O→2LiHCO3 ð12Þ 2LiHCO3→Li2CO3 þ CO2 þ H2O: ð13Þ Medina and El-Naggar (1984) developed an alternate method of chlorination to treat spodumene with a recovery of ~ 87% Li by roasting at 1150 °C with a mixture of 8:1 (wt.) tachyhydrite:spodumene follow- ed by water leaching. Because the production of lithium carbonate from spodumene is energy intensive and expensive, lithium carbonate is mostly produced from the brines. 3.2. Lithium extraction from brines/sea water/bitterns In order to meet the growing demand of lithium, brines and bitterns have received increasing attention. Tables 7 and 8 elaborate the summa- ry of work carried out recently for the extraction of lithium from sea water/brines/bitterns. Production process for brine-water lithium costs 30% to 50% less than that of the mined ores (Abe, 2010). As mentioned earlier, lithium carbonate is produced from brines by an evaporative con- centration and refining method. Firstly, brine is concentrated by solar evaporation over a year in a pond to crystallize sodium, potassium and magnesium chlorides. During the refining process calcium carbonate is roasted and then added to the solution of LiCl for the removal of 2LiF⋅KF⋅Al2O3⋅3SiO2 þ 4H2O→Li2O⋅Al2O3⋅2SiO2 þ 2KAlSi2O6 þ 4H2 þ 2F2: ð5Þ Extraction of lithium from a zinnwaldite containing waste was inves- tigated by Jandová et al. (2009). The concentrate (1.40% Li) obtained from dry magnetic separation of the waste (0.21% Li) was treated by the gypsum roast method (with CaSO4 and Ca(OH)2). About 96% Li was leached out from the sinter made at 950 °C. Earlier the concentrate prepared from this waste by gravity and dry magnetic separation, was roasted by the gypsum method at 975 °C and water leached to recover ~93% Li (Kondás and Jandová, 2006). In another study Jandová et al. (2010) reported that the roasting of the above concentrate with CaCO3·Li2CO3 with 99.5% purity was separated from the leach liquors by either converting the alkaline liquor to the carbonated solution by CO2 bubbling or by solvent extraction with LIX54 and TOPO as an extractant followed by stripping with diluted H2SO4; the first method provided a higher yield. Siame and Pascoe (2011) obtained recovery of ~84% Li from the roasted zinnwaldite concentrate at 1050 °C with lime- stone, gypsum and sodium sulfate. A similar process was reported by Vu et al. (2013) from zinnwaldite by sintering with CaCO3 powder at 825 °C, followed by water leaching and precipitation. Crocker and Lien (1987) reported the recovery of N 85% Li by roasting montmorillonite type clays (0.3–0.6% Li) with KCl–CaSO4 or CaCO3– CaSO4 followed by water leaching. Lithium silicate in the clay was con- verted to Li2SO4 by roasting a pelletized mixture of clay, limestone and gypsum at 900 °C in a direct gas-fired rotary roaster (Lien, 1985). Formation of lithium sulfate may be represented by reactions (6) and (7) CaSO4 2H2O þ SiO2→CaSiO3 þ SO2 þ 12 O2 ð6Þ Li2Si2O5 þ SO2 þ 12 O2→Li2SO4 þ 2SiO2: ð7Þ The initial product obtained from the alkaline process is lithium hydroxide which can be converted to carbonate or chloride salt. 3.1.3. Chlorination process A less common method is the chlorination process in which the ore is roasted in the temperature range 880–1100 °C in the presence of chlorine gas or HCl depending upon the type of mineral treated (Table 6). For instance chlorination of lepidolite with HCl can be achieved at lower tem- perature (935 °C) while giving a high yield (~100%) of lithium during leaching as compared to the roasting of spodumene (Löf and Lewis, 1942). Lithium in spodumene can be converted to LiCl almost quantita- tively at higher temperature (1100 °C) in 2.5 h with Cl2 gas (Barbosa et al., 2014); the recovery is found to be quite low (58%) at the lower temperature (1000 °C) (Peterson and Gloss, 1959). In the chlorination process, when the ore is sintered with NH4Cl and CaCl2 in a furnace at P. Meshram et al. / Hydrometallurgy 150 (2014) 192–208 197PDF Image | Extraction of lithium from primary and secondary sources
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