Common Chemical Inhibitors

Common inhibitors [1]: sodium sulfide, zinc sulfate, sodium cyanide, potassium dichromate, sodium silicate, lime, xanthate, tannin, starch (dextrin), carboxymethyl cellulose, etc.

Sodium sulfide

Sodium sulfide is the activator of nonferrous metal oxide ore, and it is also the inhibitor of sulfide ore when the added amount is large enough. The preparation of sodium sulfide is to reduce sodium sulfate (Na2SO4) with coal, wood carbon and other combustion as reducing gas. The reaction formula is: Na2SO4+2C=Na2S+2CO2 ↑

Sodium sulfide is used as a depressant of sulphide ore in flotation operation, sodium sulfide is used to inhibit pyrite in the production practice of molybdenum separation, kerosene is used as the collector to float molybdenite. Because the natural floatability of molybdenite is not restrained by sodium sulfide, sodium sulfide suppresses pyrite, and qualified molybdenum concentrate is obtained after several times of cleaning [2].

When sodium sulfide is added to the pulp, the pulp becomes alkaline, which makes the surface of the sulfide mineral generate a hydrophilic hydrogen oxide film and become hydrophilic, thus inhibiting the sulfide mineral.

zinc sulfate

Zinc sulfate is prepared by the reaction of zinc scraps from metal processing plants with dilute sulfuric acid. Zinc sulfate is an inhibitor of sphalerite, and its effect is not very obvious when used alone. When used with alkali, sodium cyanide, sodium sulfite, etc., the inhibition effect is strong. The higher the pH value of pulp, the better the inhibition effect.

Pure zinc sulfate will not turn yellow after being stored in air for a long time, and will become white powder after being put in dry air and losing water [2]. There are various hydrates: the stable hydrate in equilibrium with water in the range of 0-39 ℃ is zinc sulfate heptahydrate, zinc sulfate hexahydrate in the range of 39-60 ℃, and zinc sulfate monohydrate in the range of 60-100 ℃. When heated to 280 ℃, various hydrates completely lose crystal water, decompose into zinc oxysulfate at 680 ℃, further decompose above 750 ℃, and finally decompose into zinc oxide and sulfur trioxide at about 930 ℃. ZnSO4 · 7H2O and MSO4 · 7H2O (M=Mg, Fe, Mn, Co, Ni) form mixed crystals within a certain range. It reacts with alkali to generate zinc hydroxide precipitation, and reacts with barium salt to generate barium sulfate precipitation

Function of zinc sulfate: it is the main raw material for making lithopone and zinc salt, as well as a printing and dyeing mordant, a preservative for wood and leather, and an important auxiliary raw material for producing viscose fiber and vinylon fiber. In addition, it is also used in electroplating and electrolysis industries, and can also be used to manufacture cables. Zinc sulfate inhibits sphalerite.

Cooling water in industry is the largest water consumption. The cooling water in the closed circulating cooling system cannot corrode and scale the metal, so it needs to be treated. This process is called water quality stabilization. Zinc sulfate is used here as a water quality stabilizer.

Sodium cyanide (potassium)

When the preferential flotation process is adopted for the polymetallic ore deposit, sodium cyanide is used to inhibit pyrite, sphalerite, chalcopyrite and other sulfide minerals. The mixed use of sodium cyanide and zinc sulfate has a very good inhibitory effect on sphalerite. When the amount of sodium cyanide is small, it can inhibit pyrite, when the amount of sodium cyanide is small, it can inhibit sphalerite, and when the amount of sodium cyanide is large, it can inhibit various copper sulfide minerals [2].

In production practice, due to the toxicity of sodium cyanide, sulfur dioxide or sodium sulfite is often used to replace it. The inhibition effect of sulfur dioxide and sodium sulfite is weaker than that of sodium cyanide. However, due to their low toxicity and easy oxidation by air, wastewater treatment is often used. The other advantage is that minerals inhibited by sulfur dioxide and sodium sulfite are easier to be activated by copper sulfate, while minerals inhibited by sodium cyanide are more difficult to be activated.

lime

Inhibition of lime on pyrite: Lime inhibits pyrite by forming hydrate films of calcium sulfate, calcium carbonate and calcium oxide on its surface.

To activate pyrite inhibited by lime, sodium carbonate and copper sulfate can be used, or sulfuric acid can be added to reduce the pulp pH to 6-7, and butyl xanthate can be added to flotation pyrite. [2] 

Quicklime is a natural rock mainly containing calcium carbonate, which is calcined at high temperature. Its main component is calcium oxide (CaO). During calcination, due to uneven fire or temperature control, under fire lime or over fire lime is often contained. Underfire lime has small slurry yield, poor quality and low utilization rate, which will not bring harm. The hydration rate of over burnt lime is greatly reduced, and it reacts with water only after hardening, resulting in large volume expansion, resulting in local bulges, cracks and other phenomena on the hardened lime surface, which is called "ash blasting" in engineering. "Ash explosion" is one of the common problems of construction quality.

The process of quick lime and water acting on quick mature lime (Ca (OH) 2) is called slaking. In the project, add a lot of water (2-3 times of the quality of quicklime) to the quicklime to ripen it into lime milk, and then flow it through the screen into the ash storage tank and "age" for at least two weeks to eliminate the harm of burnt lime. The paste obtained by precipitation to remove excess water is called lime paste. The quicklime blocks with a height of half a meter can also be sprinkled with appropriate water (60%~80% of the quicklime amount), and the powder obtained through curing is called hydrated lime powder. The amount of water added should be slightly wet with hydrated lime powder but not clustered.

Function of lime: lime has good water retention and plasticity, and is often used to improve the water retention of mortar in engineering to overcome the shortcomings of poor water retention of cement mortar. Lime inhibits pyrite. Lime has slow setting and hardening speed, low strength and poor water resistance. The drying shrinkage of lime is large, so it should not be used alone except for painting.

Phonox

Phonox is prepared from phosphorus pentasulfide and sodium hydroxide [2]. Prepare 10% aqueous solution of sodium hydroxide, and then add phosphorus pentasulfide. After stirring for 20 minutes, dilute the prepared solution to 0.5%~1%, and then put it into use. The ratio of sodium hydroxide to phosphorus pentasulfide is 1 ∶ 1.

water glass

Water glass is an inorganic colloid, which is the most commonly used inhibitor in flotation operation. Water glass has a good inhibitory effect on quartz, silicate minerals and aluminosilicate minerals (such as mica, feldspar, garnet, etc.), and is widely used as a gangue inhibitor [2].

Water glass is made by heating and melting quartz sand and sodium carbonate to form a sintered block of water glass, which dissolves in water to form a paste colloid. Its composition is complex, including sodium metasilicate Na2SiO3, sodium orthosilicate Na2SiO4, sodium disilicate Na2SiO5 and SiO2 colloidal particles. It is usually represented by Na2SiO3.

Quartz and sodium carbonate are used for firing water glass. The properties of water glass are somewhat different due to different proportions of applied materials. Generally, the ratio of Na2O to SiO2 is used to represent the composition of water glass. The ratio of mNa2O · nSiO2, n/m, is called the modulus of water glass. For water glass used for flotation, the modulus, n/m, is 2.0~3.0. The standard modulus of water glass quality is 2.2. The water glass with small modulus is strongly alkaline, while the water glass with large modulus is difficult to dissolve and has strong inhibition effect.

The inhibition effect of water glass is mainly HSiO3 - and H2SiO3. The silicic acid molecule H2SiO3 and the silicic acid ion HSiO3 - have strong hydration and are a kind of colloidal particles and ions with strong hydrophilicity. HSiO3 - and H2SiO3 have the same acid radical as silicate minerals, which are easy to adsorb on the surface of quartz and silicate minerals, forming a hydrophilic film, increasing the hydrophilicity of mineral surface, and making it restrained.