Lithium is known as "the new energy metal of the 21st century". Today, the demand for lithium resources is still increasing. Lithium is currently mainly derived from lithium ore. The main lithium-containing minerals in lithium ore are spodumene, lepidolite, lepidolite, lepidolite and lepidolite. Among them, spodumene is an important lithium mineral resource.
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At present, the beneficiation processes of spodumene mainly include: manual separation, magnetic separation, flotation and combined beneficiation. Among them, the flotation separation process is the most frequently used and widely used. In the flotation separation technology, the focus is on the choice of flotation reagents. The commonly used flotation reagents for spodumene are mainly collectors and regulators.
Single collectors are mostly used in laboratory research. Spodumene ore flotation is currently mainly divided into two processes: reverse flotation cationic collector and positive flotation anionic collector. Common reverse flotation cationic collectors are amine collectors, and the most commonly used is dodecylamine. Such agents can reverse flotation of gangue minerals such as quartz and mica in acid slurry. This method is mainly suitable for rough selection operations. But the application is not universal. The anionic collectors of traditional positive flotation spodumene are mostly fatty acid and its soap collectors, such as oleic acid, sodium oleate, naphthenic acid soap, oxidized paraffin soap, etc. The advantages of this type of collector are wide range of use, low price and strong collection ability. Its disadvantages are poor selectivity, sensitivity to temperature, intolerant of hard water, and significant fluctuations in mineral processing indexes.
The use of combined collectors can usually play a synergistic effect of multiple agents, so as to obtain the ideal flotation separation index. A domestic spodumene ore was treated with sodium oleate + oxidized paraffin soap as a combined collector, and a spodumene concentrate with a Li 2 O grade of 6% and an operating recovery rate of 62% was obtained. In the case of using oxidized paraffin soap + oximic acid as the combined collector, the raw ore with a Li2O grade of 1.25% was flotated to obtain a concentrate with a Li2O grade of 6.21% and a recovery rate of 76.30%. The use of combined collectors can significantly improve the mineral flotation separation effect and reduce the dosage of chemicals, thereby significantly improving the economic benefits of the enterprise.
In recent years, new and efficient collectors for spodumene flotation have emerged. Most of the high-efficiency collectors developed for spodumene flotation are chelating collectors. Although it has the characteristics of good selectivity and excellent performance, the price is generally high. In practical production applications, its promotion has certain difficulties.
Spodumene ore flotation regulators are mainly "three alkalis", namely Na2CO3, NaOH, Na2S and CaCl2.
Activation effect of regulator and metal ions: The hydroxyl complexes generated by metal ions under neutral or weak alkaline conditions have high adsorption, which can greatly improve the collection ability of minerals, thereby improving the flotation effect.
The effect of regulators and traditional inhibitors: when calcium chloride, sodium carbonate, sodium hydroxide and other alkaline regulators are added, the sludge composed of silicate minerals in the pulp will react with alkali to form a certain amount of sodium silicate . It is an inorganic inhibitor by itself and has the same effect on flotation as the addition of traditional inhibitors. Therefore, inorganic inhibitors are not deliberately added in flotation practice.
Effects of modifiers and new inhibitors: among the new inhibitors, citric acid and lactic acid have weak selectivity for the inhibition of spodumene and beryl. Tartaric acid and oxalic acid were highly inhibitory to the two minerals, but were not selective. Na2S, sodium hexametaphosphate and disodium EDTA have strong inhibition and selectivity. Among them, the selective inhibition of spodumene by disodium EDTA is better.
Crazing: The condition in which a ceramic glaze shrinks more upon cooling than the body it is fired upon, thus placing the glaze in sufficient tension to crack. Such glaze cracks are referred to as craze lines.
Lepidolite: A naturally occuring mica mineral containing about 4% lithium oxide plus about 9% potassium oxide.
Petalite: A lithium aluminum silicate mineral with a high silica content, more than 4% lithium oxide, and relatively insignificant amounts of other fluxes.
Shiver: The condition in which a ceramic body shrinks more upon cooling that the glaze fired onto it, thus placing the glaze in sufficient compression to rupture its bond with the body and pop pff the surface of the ware.
Spodumene: A lithium-aluminum silicate mineral currently available with well over 7% lithium oxide.
Potash feldspars may contain, in total, more than 14% sodium and potassium oxides by weight. At 7.7% lithium oxide by weight, a familiar commercial spodumene appears to contain much less flux. Such thinking, of course, is entirely wrong.
The most common error made in the formulation of glazes containing lithium in any form is to overlook the critical fact that lithium weighs less per atom than any other flux element on earth. Since fluxing power is due to the number of flux atoms present in a glaze, rather than the weight of those atoms, the challenge of lithium is to avoid adding too much of it.
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To visualize this in action, consider simply replacing a potash feldspar in a glaze recipe with an equal weight of spodumene. What will the result be? First, the new recipe will have more alkali flux than before. Recall that lithium, sodium, and potassium are all alkali flux elements.
The recipe will also have more alumina and less silica than before. To bring the glaze recipe back close to what it was originally requires adding silica (sometimes called flint) and reducing alumina by using less clay.
However, of possibly greater importance, the coefficient of thermal expansion (CTE) of the glaze will be sharply lower. As a result, the glaze may shiver off rims and other sharp edges of ware after firing.
The point, of course, is that like many other glaze ingredients, spodumene cannot simply be substituted for another feldspar in a glaze recipe on a weight-for-weight basis without changing the fired result.
In the case of spodumene, careful use of glaze calculation software is the most efficient way to bring lithium into the glaze recipe without producing undesirable changes to the fired glaze.
Some spodumene sources produce a relatively coarse product. Ideally all glaze ingredients would pass through a 200-mesh sieve. It is wise to at least dry sieve a sample of a new batch of spodumene through an 80-mesh sieve. Any spodumene that will not pass through that sieve would settle out quickly in the glaze bucket, so it should be either discarded or set aside to be ground fine enough to use.
A number of other sources of lithium have been used in glazes and clay bodies including frits, petalite, lepidolite, and lithium carbonate. However, spodumene is easily the most affordable lithium source available.
In a studio situation where a mixed glaze may remain in a tightly closed bucket for a long period of time, lithium carbonate may present serious problems if one is twice-firing. The first firing, of course, burns organics out of the body, drives off water, and strengthens the ware while commonly leaving it sufficiently porous to absorb water from the applied glaze.
The problem with lithium carbonate is it is somewhat soluble in cold water. Left to sit long enough in the glaze slurry, some lithium carbonate will dissolve. The lithium in solution then migrates, in the evaporating water from the glaze slurry, to the surface of the ware as it dries (see diagram at left).
That creates a local concentration of lithium at the glaze surface, which can be high enough to cause shivering at that point. In extreme cases of lithium carbonate dissolving in a glaze, both crazing and shivering have been reported on the same fired piece!
The fact that lithium lowers the CTE of a fired glaze can be an advantage, however, as long as the lithium remains undissolved. Small amounts of spodumene, which contains lithium in a less soluble form than lithium carbonate, are frequently added to glaze recipes to lower glaze expansion and reduce or eliminate glaze crazing.
Glazes that have been designed to fit stoneware clay bodies will typically craze on porcelain clay bodies fired to the same temperature. Likewise, glazes that do not craze on porcelain clay bodies will typically shiver on edges of ware made from stoneware clay bodies fired to the same temperature. Small replacements of the potash feldspar in a glaze recipe with spodumene on a one for one basis have a significant effect on glaze fit. The following calculations illustrate this.
The glaze has a calculated SiO2:Al2O3 ratio of ~9.38 and a CTE of 7.29. A direct substitution of spodumene for the potash feldspar in the recipe (40% spodumene) produces a calculated SiO 2:Al2O3 ratio of ~7.06 and a CTE of 5.53. The silica to alumina ratios are in a range where both glazes will be glossy and any fired difference will not be visible. The spodumene version, however, with its very dramatically smaller CTE, may shiver seriously off any sharp edge.
I’ve used quite a bit at cone 10. When using it with porcelain, I have substituted talc for some of the whiting as well as adding a small amount (5%) of spodumene to reduce the CTE. The CTE of porcelain bodies has a wide range, affected both by the amount of silica in the recipe and the firing temperature (degree of vitrification). The point of the tests is not to show that spodumene causes shivering, because it doesn’t unless one uses an excess of it, but rather that from this extreme example it is clear spodumene has a significant effect on lowering glaze expansion and in small, calculated additions can improve the glaze fit of an otherwise crazing glaze.
Subjecting the test tiles to several consecutive cycles of cooling in a freezer for a half hour or so followed by being gently placed directly into boiling water should prove that point. This will be more apparent in glazes with dark colorants fired onto a light stoneware body.
the author Dave Finkelnburg is a studio potter and practicing engineer. He earned his master’s degree in ceramic engineering from Alfred University.