Cassiterite chemical formula SnO2, tetragonal crystal structure, symmetry L44L25PC, with a rutile structure, oxygen ions approximately hexagonal closest packing, tin ions located in the octahedral oxygen ions consisting of six, And constitute SnO6 octahedral coordination. SnO6 octahedrons are arranged in a straight column along the c-axis direction, and each SnO6 octahedron has two ridges adjacent to two adjacent SnO6 octahedrons. The variation in the size of the cassiterite cell is related to the replacement of the isomorphism of the impurity in the crystal lattice. After the cassiterite crystal is broken, the surface is lined with O2– ions and Sn4+ ions. From the beginning of grinding, the cassiterite particles react with water to form a hydrate on the surface of the particles. The zero point of the surface of the cassiterite is due to the inclusion of various impurities in the crystal lattice. These impurity atoms are close to the radius of the cassiterite atom, and the tin atom in the cassite lattice is often replaced by the isomorphic form so that the pH of the zero point is Change within a certain range.

2 Dissolution characteristics of tin minerals

Pure cassiterite has almost no chemical reaction and its solubility is very low, and the concentration of ions formed in the solution is negligible. With the change of temperature and time, the cassiterite has a hydroxylation process in the aqueous medium. At a temperature of 25 ° C, the dissolution of tin dioxide in the range of pH 2-11 is not dependent on pH, but forms a soluble medium. Sex molecules, according to the distribution of the composition of the cassiterite solution at different pH, Sn(OH)4 is dominant in the case of solution pH>1.2. The relationship between tin (IV) hydroxide ligand and pH is regular. When the H+ concentration in the aqueous solution is high, the surface of the cassiterite is positively charged, and when the OH-concentration in the aqueous solution is high, the surface of the cassiterite is negatively charged. Under acidic conditions, the cassiterite in the solution mainly exists in the state of Sn4+, Sn(OH)3+, Sn(OH)22+, Sn(OH)3+. Under alkaline conditions, it is mainly in the form of Sn(OH)5-, Sn(OH)62-.

3 The role of metal ions in the cassiterite flotation system

Benzohydroxamic acid is a good collector of cassiterite. Under the appropriate concentration, temperature, pH and stirring force, the recovery rate can reach 80%. It has poor ability to collect calcite . The recovery rate is only 20%. %, but there is no capture effect on quartz . In the benzyl hydroxamic acid flotation system, among the four metal ions Cu2+, Fe3+, Ca2+ and Pb2+, Pb2+ is the only metal ion that can activate cassiterite, which can increase the recovery rate of cassiterite by 5%, and the other three ions are all It has a certain degree of inhibition on cassiterite. The inhibition strength is Cu2+, Fe3+, and Ca2+. Pb2+ can also effectively activate calcite. The recovery rate after activation can be increased from 20% to 80%. The other three metal ions are calcite. The effect is not large; there is no significant change in the flotation behavior of quartz after interaction with four ions. Infrared spectroscopy indicated that chemisorption occurred between benzyl hydroxamic acid and cassiterite. The addition of Pb2+, Fe3+ and Cu2+ changed the interaction between the cassiterite and the agent, resulting in a corresponding change in the recovery rate. The adsorption amount measurement found that Pb2+ increased the amount of drug adsorption, while the other three ions reduced the adsorption amount. Actual tests show ore, iron ore and a magnetic metal sulfide ore cassiterite flotation can be suppressed, so that a suitable iron removal rate and desulfurization rate is one of the key factors cassiterite recovered, the conditions at 0.36% of the tin-containing ore, can The result of closed circuit test is 30.18% of the tin concentrate and 62.44% recovery rate.

4 Mechanism of flotation process of cassiterite carrier

The physico-chemical basis of the flocculating of the cassiterite carrier is that the surface of the carrier cassiterite and the fine cassiterite is selectively hydrophobic by the benzoic acid, and then close to each other, collide and adhere to form coarse granules by high-speed stirring. Agglomerates with fine particles, thereby increasing the possibility of adhesion of fine-grained cassiterite to bubbles. Hydrophobic cassiterite is more likely to agglomerate than hydrophilic cassiterite; in the presence of coarse cassiterite, the agglomeration is more obvious than in the absence of coarse granules, and only when the particle size of cassiterite is constant, fine particles can be adhered. Xi Shi. The carrier effect is most pronounced when a particle size particle having hydrophobicity is present. The electrostatic interaction between the cassiterite particles is only related to the charge of the particles themselves, and the hydrophobic interaction force of the fine intergranular cassiterite is much larger than the van der Waals force between the particles. Therefore, it can be judged that the main force of the particle cassite flocculation is the hydrophobic force between the particles, that is, the hydrophobic force in the carrier flotation will play a decisive role.

5 Effect of particle bubble interaction on the flotation of cassiterite

The factors affecting the recovery rate of fine-grained cassiterite flotation are mainly particle size, bubble size, bubble volume, pH value, and stirring strength. There is an optimal matching range between the cassiterite and the bubble, the pharmacy system is different, and the matching range is different. The results show that the hydroxamic acid and salicylic acid, tributyl phosphate system, -10μm, -20 + 10μm, -38 + 20μm three size fractions were cassiterite particles and 45-59μm, 59 m, bubble size about 69μm match . In the MOS system, the bubble sizes matched by the four particle sizes of -10 μm, -20 + 10 μm, -38 + 20 μm, and -74 + 38 μm are 69 μm, 69 μm, 45 - 59 μm, and 69 μm, respectively. Both the increase in collector and electrolyte concentration can cause agglomeration between the particles and the bubbles, thereby increasing the apparent particle size of the particles - bubbles. The average bubble size of the 38 μm, 50 μm, 74 μm, 150 μm, 250 μm, 420 μm, and 1000 μm cathode aperture cuts were: 20.2 μm, 29.5 μm, 44.6 μm, 59.2 μm, 68.7 μm, 78.5 μm, and 88.8 μm, respectively. The amount of bubbles, size, velocity, and bridging between bubbles are greatly affected by current, electrolysis time, and electrolyte concentration. When the pH is about 4.5 and the MOS dosage is 100 mg/L, the flotation of the cassiterite mineral is better.

Collision adhesion mechanism in 6 fine-grained cassiterite flotation system

The probability of sticking of cassiterite-bubble depends mainly on the collision efficiency of cassiterite-bubble. Once the colloidal gangue collides with the bubble, the probability of adhesion between the two is great. The sillimanite-free change of free energy before and after contact and adhesion between the bubbles ΔG is more negative, and the cassite is more likely to adhere to the bubbles. The high-speed camera was used to track the cassiterite-bubble collision-adhesion-desorption process. The results show that the sillimanite-bubble collision-adhesion-desorption mode and the probability of occurrence are very different under different conditions. The agglomeration between bubbles of different sizes is different due to the rising speed and the amount of cassiterite particles carried. The probability of adhesion after collision is different. The larger size of the bubble surface carries more cassiterite particles, the load is larger, and the rising speed The probability of adhesion to the cassiterite particles carried by the small bubbles is low. Bubbles of substantially the same size and rate of rise – the cassiterite agglomerates are more likely to adhere to form larger agglomerates and eventually reach the purpose of floating.

The collision, adhesion, and capture models were used to calculate the collision, adhesion, separation, and capture probability. The results showed that the collision probability decreased significantly with the decrease of particle size and the increase of bubble size (<150μm). An effective collision facilitates an increase in the probability of adhesion, thereby contributing to an increase in flotation recovery.

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