Inhibitor – Sodium Carboxymethyl Cellulose (CMC)
Sodium Carboxymethyl cellulose, whose industrial products are light yellow floccules, has relatively stable chemical properties and is soluble in water.
Sodium Carboxymethyl cellulose is a potent inhibitor of silicate minerals containing magnesium such as pyroxene, serpentine, hornblende, kaolin and chlorite, and also has inhibiting effects on quartz, carbonaceous gangue and shale gangue (weathering products of silicate minerals). For the nickel ore flotation, the use of Sodium Carboxymethyl Cellulose to inhibit pyroxene and hornblende can achieve better results than that of water glass.
Sodium Carboxymethyl Cellulose is widely used to inhibit calcium silicate minerals, carbonaceous gangue and shale gangue. The inhibitory effect of cellulose is because after the reaction with mineral particles, it can combine with water by such polar groups as —O—, —OH, and—COOH, and the mineral particles by its effect then become hydrophilic.
Mechanism of Sodium Carboxymethyl Cellulose Inhibiting Gangue Minerals
1. Establishment of Sodium Carboxymethyl Cellulose Absorption Model
(1). The metal ions on the mineral surface (ca2, M, Fe2, Fe3 ) can produce absorption with the polar groups of Sodium Carboxymethyl Cellulose (一OH, 一COOH) by electrostatic forces.
(2). The metal ions on the mineral surface can generate a chemical reaction with the carboxyl groups of inhibitor to form strong chemical bonds.
(3). The carboxyl and hydroxyl groups in the Sodium Carboxymethyl Cellulose molecules can provide with protons, while the oxygen in the silicate and phosphate, the carboxyl group on the surface of carbonate minerals, and the fluorine on the surface of fluorite minerals can accept minerals. Then by means of the generation of hydrogen bonds, part of the polar groups in Sodium Carboxymethyl Cellulose will be absorbed on the mineral surface, while many other hydroxyl groups will associate with water by hydrogen bonds to make the mineral surface hydrophilic.
(4). The unavoidable ions adsorbed on the surface of silicate in the slurry can produce the secondary adsorption by the carboxyl groups provided by inhibitors to generate chemical bonds, thereby reducing the unavoidable ions in the slurry and achieving the purpose of preventing activation. From the perspective of the Sodium Carboxymethyl Cellulose molecular structure, the metal ions on the mineral surface can produce adsorption with the polar groups by the electrostatic force. However, the electrostatic force is generally small, this kind of adsorption does not play a major role.
In addition, the metal ions on the mineral surface may produce chemisorption with carboxyl groups. However, since the inhibitor belongs to the macromolecular compound, the collecting agent and the metal ions on the mineral surface produce the competitive adsorption. Therefore, this kind of adsorption also does not play a major role. And it is only the third way that really works. Hydrogen bonds are formed by numerous 一OH and 一COOH in the molecules and the anionic active particles on the surface of such minerals as carbonates, phosphates, silicates and fluorite, while other carboxyl and hydroxyl groups will be associated with water, making the mineral surface hydrophilic and achieving the inhibiting purpose.
Test results also show that Sodium Carboxymethyl Cellulose as the inhibitor of gangue minerals has removed the vast majority of carbonate and phosphate minerals such as dolomite, calcite, barite, monazite, apatite, quartz, feldspar, and most of fluorite; removed most of the silicate minerals such as achmatite achmite (amphibole) and biotite.
The reason why the ability of Sodium Carboxymethyl Cellulose to inhibit the iron-containing silicate is weaker than that of carbonate, phosphate and fluorite minerals may be that alkyl hydroximic acid salts and Sodium Carboxymethyl Cellulose simultaneously produce the competitive adsorption on the iron ions on the surface of silicate minerals, and alkyl hydroximic acid salts have formed stable chelates with iron ions, thus reducing the inhibiting ability of inhibitor and making part of silicates become foam products. However, the chelates generated by the calcium ions on the surface of carbonate and alkyl hydroximic acid salts are very unstable and prone to decomposition. Therefore, in the presence of Sodium Carboxymethyl Cellulose, the collecting agent on the surface of carbonate will be continually desorbed, while the inhibitor reacts with the mineral surface, so that the gangue minerals containing calcium ions are well inhibited.
(1). In the sorting of niobium minerals, the carboxyl hydroxyl groups in the Sodium Carboxymethyl Cellulose molecules are not only fixed on the surface of the inhibited minerals, but also function as the hydrophilic groups. The carboxyl and hydroxyl groups in its molecules, by providing protons, can combine with the oxygen in the silicate and phosphate, the carboxyl group on the surface of carbonate minerals, and the fluorine on the surface of fluorite minerals to form the hydrogen bonds, so that part of the polar groups in Sodium Carboxymethyl Cellulose will be absorbed on the mineral surface, while many other hydroxyl groups will associate with water by hydrogen bonds to make the mineral surface hydrophilic.
(2). Sodium Carboxymethyl Cellulose is the effective inhibitor of such gangue minerals as carbonate, fluorite and phosphate minerals in the sorting of niobium minerals.
(3). In order to remove the vast majority of iron-containing silicate minerals, the combined use of Sodium Carboxymethyl Cellulose and other inhibitors should be considered.
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