Why should use defoamer for Phosphoric acid? How to use defoamer in the Phosphoric acid?

In the production of wet-process phosphoric acid, when the content of carbonate and organic matter in the phosphate rock powder is high, a large amount of CO₂ gas is generated by chemical reaction with the acid. With the fierce progress of the acid hydrolysis process, CO₂ is continuously dispersed in the reaction liquid containing organic components, forming a stable foam layer on the surface of the slurry, and its volume can usually reach 5% to 10% of the volume of the reaction liquid.

Production brings many adverse effects: first, it affects the dispersion and acid hydrolysis reaction of phosphate ore pulp, which reduces the production capacity; second, the foam layer not only reduces the equipment utilization rate, but also makes it difficult to observe the material level; third, it hinders the reaction process The evaporation of middle water and the removal of heat cause the reaction temperature of the extraction tank to rise. In severe cases, the foam will be taken to the exhaust gas absorption system and even to the diffuser tank, causing loss of P₂O₅ and environmental pollution.

Reaction which occurs during phosphoric acid production without defoamer

 Analysis of foaming factors in wet-process phosphoric acid production

In the process of wet phosphoric acid production, there are many factors that affect foaming, and it is simply summarized as follows:

Ø  Carbonate and organic content in phosphate rock. This is an important index that affects the foaming performance.When the content of carbonates and organics is small, the CO2 gas produced by acid hydrolysis is very small, and the foam formed is very thin and unstable, that is, the foamability of the phosphate rock. weak.

Ø  Stirring intensity. The process of foam generation and disappearance is also different when the stirring intensity is different. If the stirring intensity is large, the foam generation time is prolonged and the disappearance time is shortened.

Ø  Thickness of phosphate rock. The finer the phosphate rock, that is, the larger the specific surface area, the more intense the foaming phenomenon, and the resulting foam layer is both high and stable.

Ø  Reaction temperature. The reaction temperature has a significant effect on the swelling of the foam, because the liquid viscosity and surface tension are related to temperature. The reaction temperature is too high or too low, which is conducive to suppress foaming.

Ø  MgO impurity content and liquid phase P2O5 content in the phosphoric acid slurry. The higher the content of MgO impurities and liquid P2O5, the greater the viscosity of phosphoric acid and the more stable the foam. And the higher the sulfuric acid content, the greater the amount, the better the stability of the foam.

 Analysis of the reasons for the overstability of foam in wet-process phosphoric acid production

China is rich in phosphate rock resources, and its reserves rank fourth in the world, but more than 70% are low-grade siliceous calcareous phosphate rock ore (ie colloidal phosphate rock).

These low and medium grade phosphate ore usually need flotation to meet the requirements of wet process phosphoric acid production. The organic matter remaining in the phosphate rock during the flotation process, such as pulp waste liquid, has the dual functions of collection and foaming.The effective ingredients are fatty acids and soaps (w = 16.42%) and resin acids and soaps (w = 17.67). %).

Fatty acids are mainly linear unsaturated acids, such as oleic acid, linoleic acid, and  linolenic acid. Resin acids are mainly deoxyabietic acid and dihydroabietic acid. The surface tension of these surface-active substance solutions is very low. When they exist in the system, the surface free energy of the foam system will be greatly reduced; on the other hand, when the liquid film of the foam is impacted, the surface area will increase at the local thinning point. The density of the adsorbed surface active molecules decreases and the surface tension increases, which causes the nearby surface active molecules to try to migrate to a thinner place, so that the surface adsorbed molecules are restored to the original density and the surface tension is reduced to the original level. During the migration process, the active molecules move with the adjacent solution together, so that the thinned liquid film increases to its original thickness and maintains the stability of the foam. This surface tension repair effect is the pulp waste liquid surfactants to maintain the foam stability. Factor. Due to the existence of the repair effect, the liquid film has a certain elasticity. In addition, fatty acid soaps, which are anionic surfactants, are enriched on both sides of the foam liquid film due to adsorption, making both surfaces of the liquid film negatively charged, and counterions are dispersed in the liquid film solution to form a surface electric double layer. When the liquid film becomes thin, the electrical repulsion between the two surfaces prevents it from further thinning. This electrical repulsion is another factor that keeps the foam stable from pulp waste liquid surfactants. From the perspective of the strength of the adsorption membrane, pure ionic surfactants are adsorbed at the gas-liquid interface. Due to the repulsion of polar group charges, they cannot be approached. They are loosely arranged at the gas-liquid interface, and the formed adsorption membrane has a lower viscosity. Weakness. Among the active ingredients of pulp waste liquid, there are both ionic fatty acid soaps and molecular fatty acids. They co-adsorb at the air-liquid interface, and molecular fatty acids are interposed between fatty acid root ions to form a complex. Tight, the strength of the formed adsorption film is large, which leads to the increase of the foam life. This is one of the factors that maintain the foam stability of the pulp waste liquid surfactants. It is also a more important factor..

Wet Method Phosphoric Acid Production

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