Carboxymethyl cellulose (CMC) is a commonly used flotation depressant. The following briefly introduces the mechanism of action of CMC in the flotation of talc and pentlandite.
1. Talc
The inhibitory effect of carboxymethyl cellulose (CMC) on talc is inseparable from the adsorption of CMC on the surface of talc and the change of the dynamic potential on the surface of metal sulfide ores caused by CMC. Studies have shown that as the number of washings increases, the desorption amount of CMC increases, and the flotation recovery rate of talc slowly increases, which indicates that the desorption is slow. At the same time, calcium ions play an important role in the adsorption process of CMC on the surface of talc. It may change the configuration of the polymer in the solution and may also act as a linker. CMC adsorption of talc is physically adsorbed through hydrophobic bonding and hydrogen bonding. Some scholars also believe that the carboxyl group in CMC reacts chemically with the cations on the surface of talc. The effect of CMC on minerals may also include bonding or complexation between the cations on the surface of minerals and polymers.
CMC can significantly enhance the wettability of the talc particle layer and end surface and make them consistent, thereby better inhibiting the talc that floats due to surface hydrophobicity and realizing the flotation separation of sulfide ore and talc. However, CMC cannot prevent a small amount of talc from floating due to foam entrainment.
CMC can enhance the negative charge of the talc surface and make the talc more dispersed in water, but this is not beneficial to its inhibition of talc. On the contrary, the aggregation between particles that can cause the surface area to decrease is conducive to the inhibition of talc.
CMC is adsorbed on the layer and end surface of talc through the dual effects of hydroxyl and carboxyl groups.
The inhibitory effect of CMC on talc is also closely related to the degree of polymerization of CMC, the pH value of the solution, the concentration of metal ions, etc. The degree of polymerization not only determines the molecular weight of CMC, but also affects the strength of the negative charge of CMC; low pH value and high metal ion concentration are conducive to promoting the inhibition of CMC on talc.
2. Pentlandite
CMC has two strong polar groups, namely -OH and -COOH. In water, -COOH dissociates into –COO-, which is a negative point for CMC. When the pH value of serpentine in flotation pulp is less than 9, the surface of serpentine has a positive point. Therefore, CMC is adsorbed on the surface of serpentine through electrostatic adsorption. The -OH group of CMC adsorbed on the surface of serpentine forms hydrogen bonds with water molecules, forming a layer of water film on the surface of serpentine ore mud, which inhibits serpentine ore. In addition, CMC can also chemically adsorb with metal ions on the surface of serpentine, thereby inhibiting serpentine ore mud.
