In the family of mineral processing agents, there is a type of natural polymer agent derived from crops——starchIt is not only a staple food source on the dining table, but also an efficient and environmentally friendly inhibitor in fields such as iron ore reverse flotation and phosphate ore flotation. Compared with traditional chemical inhibitors, starch has outstanding advantages such as wide source, low cost, non-toxic and harmless, and good selectivity, and is known as a model of "green mineral processing agents". This article will provide you with a comprehensive introduction to this natural mineral processing aid.

1、 What is starch?

Starch is a natural high molecular weight polysaccharide composed of glucose units connected by glycosidic bonds, with the chemical formula (C ₆ H ₁ ₀ O ₅) ₙ. It is widely found in crops such as corn, potatoes, cassava, and wheat. It appears as a white powder and is insoluble in cold water, but can gelatinize and form a viscous solution in hot water.

Role in Mineral ProcessingMainly used forinhibitorSelective inhibition of iron minerals (such as hematite, magnetite), carbonate minerals (such as calcite, dolomite), etc., to prevent them from floating during flotation, thereby achieving separation from useful minerals.

Common sources：

• corn starchMost commonly used, low price, wide source

• cassava starchHigh viscosity, strong inhibitory ability

• potato starchMedium viscosity, low gelatinization temperature

• wheat starchContains protein impurities, slightly less effective

The most commonly used in mineral processing plants iscorn starchandcassava starch。

2、 Why do we need starch?

The core challenge of iron ore reverse flotation

In iron ore flotation, the goal is to float vein minerals such as quartz (SiO ₂), while iron minerals (hematite, magnetite) remain in the bottom stream to become concentrates. This requires aStrong inhibition of iron minerals, but little inhibition of quartzThe potion.

Conventional inorganic inhibitors (such as water glass and sodium hexametaphosphate) have limited selective inhibitory ability on iron minerals. Starch, due to its abundant hydroxyl groups (- OH) in its molecules, can selectively undergo chemical adsorption or hydrogen bonding with iron ions on the surface of iron minerals, thereby strongly inhibiting iron minerals and having almost no effect on quartz.

Simple metaphorStarch is like a "net" that "wraps" iron mineral particles, preventing them from adhering to bubbles, while quartz is not affected and can float normally.

3、 The core characteristics of starch

1. Excellent selectivity

Starch has a strong inhibitory effect on iron minerals such as hematite and magnetite, while its inhibitory effect on vein minerals such as quartz and silicate is extremely weak. It is a key agent for achieving efficient separation of iron minerals and quartz.

2. Green and environmentally friendly

Starch is a natural organic polymer that is non-toxic, biodegradable, and does not cause persistent pollution to the environment, meeting the requirements for the development of green mines.

3. Wide source and low cost

Starch comes from crops such as corn and cassava, with abundant resources and low prices (about 3000-5000 yuan/ton), and controllable mineral processing costs.

4. Easy to use

Starch can be prepared into a solution through gelatinization or alkaline dissolution, making it easy to add and use.

4、 The main application scenarios of starch

The most classic applicationRed iron ore reverse flotation. The vast majority of hematite beneficiation plants worldwide use the reverse flotation process of "starch+lime+fatty acids", where starch inhibits hematite and fatty acids capture quartz to obtain high-quality iron concentrate.

5、 The mechanism of action of starch

The inhibitory effect of starch on iron minerals is based on the following mechanism:

1. chemisorptionThe hydroxyl group (- OH) in starch molecules forms chemical or hydrogen bonds with iron ions on the surface of iron minerals, firmly adsorbing.

2. Hydrophilic membrane coverageThe starch molecular chains adsorbed on the surface of iron minerals form a hydrophilic film, which prevents the adsorption of fatty acids and other collectors.

3. steric hindranceLong chain starch molecules form a three-dimensional barrier on the mineral surface, preventing collectors from approaching.

Simple understandingStarch is like a layer of "water film" wrapped around the surface of iron minerals, making it difficult for collectors to recognize them and only able to capture quartz.

6、 How to use starch

1. Preparation (gelatinization)

Dry starch is insoluble in cold water and must pass throughgelatinizationorAlkali solubleProcessing is necessary to prepare a solution:

Method 1: Heating gelatinization (most commonly used)

• Mix starch with water in a ratio of 1:10-1:20 and stir

• Heat to 80-95 ℃ and hold for 20-40 minutes until the solution becomes transparent and viscous

• Cooling backup

• The preparation concentration is usually 2% -5%

Method 2: Alkali dissolution method (at room temperature)

• Mix starch with a small amount of water to make a paste

• Add sodium hydroxide (NaOH, approximately 5% -10% of starch content)

• Stir for 10-20 minutes, starch dissolves into a viscous liquid

• Dilute with water to the desired concentration

• Suitable for occasions where heating is not appropriate

attention：

• Gelatinization must be sufficient, otherwise undissolved starch granules will precipitate and become ineffective

• The viscosity of the gelatinized starch solution is high, and it should be diluted to 1% -2% before adding

• Starch solution is prone to spoilage (microbial growth), it is recommended to prepare and use it on the same day

2. Add points

• Generally joinedball millorMixing tankIn the middle.

• Require thorough mixing with the slurry for 3-5 minutes.

• Usually, starch is added first to suppress iron minerals, followed by pH adjusters and collectors.

3. Order of addition (hematite reverse flotation)

Typical sequence:

1. starch(Inhibiting hematite)

2. lime(Adjust pH to 10-11)

3. fatty acid(Capture quartz)

4. foaming agent(Pine alcohol oil, etc.)

4. Typical dosage

(Note: The specific dosage needs to be determined through flotation tests)

5. Precautions

• Accurate control of dosageInsufficient starch leads to incomplete inhibition of iron minerals and low grade of iron concentrate; Excess starch may cause slurry stickiness and foam abnormalities, and increase costs.

• Fully gelatinizedUngelatinized starch granules will settle at the bottom of pipelines and tanks, which not only wastes chemicals but may also cause blockages.

• Preventing corruptionDuring high temperatures in summer, starch solutions are prone to spoilage (such as sourness and odor). Therefore, it is recommended to reduce the preparation amount, shorten the storage time, or add a small amount of preservatives (such as formaldehyde).

• Water quality impactCalcium and magnesium ions in hard water may form precipitates with starch, reducing the effect. The dosage can be appropriately increased.

7、 Factors affecting the effectiveness of starch

8、 Comparison between Starch and Other Inhibitors

Selection suggestion：

• Inhibition of iron minerals (hematite, magnetite): Starch is preferred

• Inhibit quartz and silicates: choose water glass

• Inhibition of Calcite and Dolomite: Selecting Sodium Hexametaphosphate

• Inhibition of talc and graphite: choose CMC

9、 Substitution and combination of starch

Alternative drugs

use in combination

• Starch+water glassStarch inhibits iron minerals, while water glass inhibits silicate gangue (used for iron ores containing multiple types of gangue)

• Starch+Sodium HexametaphosphateInhibition of iron minerals+carbonate gangue

• Starch+LimeStarch inhibits iron minerals, lime adjusts pH and inhibits pyrite

10、 Safety and Environmental Protection of Starch

1. Security

• toxicityStarch is non-toxic, with LD50 (oral administration to rats)>5000 mg/kg, and is considered a practically non-toxic substance.

• dustDry starch dust may cause dust explosion when it reaches a certain concentration in the air, and ventilation and explosion prevention should be taken into account.

• protectionWear a dust mask during operation.

2. Environmental friendliness

• biodegradationStarch can be completely degraded by microorganisms, and the final products are CO ₂ and H ₂ O, which are environmentally friendly.

• Tailings waterThe tail water containing starch is non-toxic and can be directly discharged or reused.

3. Storage and transportation

• Store in a cool, dry, and ventilated warehouse, moisture-proof and rainproof (moisture is prone to mold and clumping).

• Avoid mixing with strong oxidants.

• Seal the packaging and secure the bag tightly after use.

• The shelf life is usually 1-2 years, but attention should be paid to insect and rodent prevention.

11、 Common Problems and Solutions

12、 Quality inspection of starch

The beneficiation plant should conduct quality inspection on the incoming starch:

Conclusion

Starch, a natural polymer derived from farmland, plays an irreplaceable role in fields such as iron ore reverse flotation. It selectively inhibits iron minerals, allowing quartz to float smoothly, providing green and efficient chemical support for the production of high-grade iron concentrate.

Unlike many chemical synthetic agents, starch is non-toxic, biodegradable, and has renewable sources, making it an outstanding representative of the "green mineral processing" concept. With the increasing demand for environmental protection, the application of starch and its modified products in the field of mineral processing will become more widespread.

Starch - the green guardian of iron ore reverse flotation and the model of natural polymer beneficiation.