In the fields of Mineral processing and geological analysis, the correct use of Flotation reagents is crucial for accurately detecting mineral compositions. Flotation is a widely applied physicochemical process for mineral separation and enrichment, relying on differences in the physicochemical properties of mineral surfaces. By adding reagents, the hydrophilicity or hydrophobicity of mineral surfaces can be adjusted, enabling the separation of target minerals from gangue.
This article will introduce a series of practical operational tips to help laboratory technicians and mining engineers optimize the flotation process, improving the accuracy and repeatability of test results.
First, let's start with the basic types of flotation reagents—Collectors, Frothers, and Modifiers. Each reagent plays a unique role in the flotation process. Collectors enhance the hydrophobicity of minerals, promoting their attachment to air bubbles; frothers help stabilize the foam layer, allowing enriched minerals to be easily separated from the slurry; modifiers are used to adjust the pH or ionic strength of the slurry, creating optimal conditions for mineral flotation.
With continuous technological advancements, the types and applications of flotation reagents are also expanding. The correct selection and use of these reagents can not only improve Mineral recovery rates and grades but also bring significant benefits in terms of environmental protection and cost control.
How to Use Flotation Reagents Correctly?
Types of Reagents
The types of reagents used in flotation plants depend on factors such as ore properties, process flow, and the number of desired mineral products. Generally, they are determined through ore selectivity tests or semi-industrial tests.
Reagents can be broadly categorized into three main types based on their functions:
Frothers: Organic surfactants that distribute at the water-air interface. They are used to generate a froth layer that can float the minerals. Common frothers include pine oil, cresylic acid, and alcohols.
Collectors: Their function is to capture target minerals, altering the hydrophobicity of mineral surfaces to allow floating mineral particles to adhere to air bubbles. Based on their nature, collectors can be divided into non-polar collectors, anionic collectors, and cationic collectors. Commonly used collectors include black medicine, yellow medicine, white medicine, fatty acids, fatty amines, and mineral oils.
Modifiers: Modifiers include activators and inhibitors, which change the properties of mineral surfaces, influencing the interaction between minerals and collectors. Modifiers also include agents used to alter the chemical or electrochemical properties of the aqueous medium, such as pH adjusters and the state of collectors. Types of modifiers include:
pH Adjusters: Lime, sodium carbonate, sulfuric acid, sulfur dioxide.
Activators: Copper sulfate, sodium sulfide.
Inhibitors: Lime, yellow blood salt, sodium sulfide, sulfur dioxide, sodium cyanide, zinc sulfate, potassium dichromate, water glass, tannin, soluble colloids, starch, synthetic polymers, etc.
Others: Wetting agents, flotation agents, solubilizers, etc.
Reagent Dosage
The dosage of reagents during flotation must be precise; insufficient or excessive amounts can affect mineral processing indicators. Excessive usage may also increase processing costs.
Relationship Between Reagent Dosage and Flotation Indicators:
Insufficient collector dosage can lead to inadequate hydrophobicity of the minerals, reducing recovery rates. Conversely, excessive amounts may lower the quality of the concentrate and complicate separation flotation.
Insufficient frother dosage can lead to poor foam stability, while excessive amounts may cause "overflow" phenomena.
Too little activator dosage can lead to poor activation, while too much may disrupt the selectivity of the flotation process.
Insufficient inhibitor dosage can lower the grade of the concentrate, while excessive amounts may suppress the minerals that should float, decreasing recovery rates.
Reagent Preparation
Solid reagents are diluted into liquids for easy addition. Water-insoluble reagents such as yellow medicine, amine black medicine, water glass, sodium carbonate, copper sulfate, and sodium sulfide should be prepared as aqueous solutions with concentrations ranging from 2% to 10%. Water-insoluble reagents need to be dissolved in a solvent before being prepared as an aqueous solution for addition, such as some amine collectors that can be directly added, like No. 2 oil, No. 31 black medicine, and oleic acid. For highly soluble reagents that require significant quantities, preparation concentrations typically range from 10% to 20%, such as sodium sulfide, which is prepared at 15% during use. For poorly soluble reagents, organic solvents can be used to dissolve them before preparing them as low-concentration solutions.
The choice of Reagent preparation method primarily depends on the properties of the reagents, the addition method, and their functions. The same reagent can have significant differences in dosage and effects due to different preparation methods. Generally, common preparation methods include:
Preparing a 2% to 10% aqueous solution: Most water-soluble reagents are prepared this way (e.g., yellow medicine, copper sulfate, water glass).
Dissolving in a solvent: Some water-insoluble reagents can be dissolved in special solvents. For example, white medicine is not water-soluble but can be dissolved in a 10% to 20% aniline solution, and must be used after preparing an aniline mixed solution. Similarly, aniline black medicine is not water-soluble but can dissolve in a sodium hydroxide alkaline solution, so an alkaline sodium hydroxide solution must be prepared first before adding the reagent to create an aniline black medicine solution for flotation.
Preparing as a suspension or emulsion: For some poorly soluble solid reagents, they can be prepared as emulsions for use. For example, lime has very low solubility in water, so it can be finely ground into powder and mixed with water to create a milky suspension (e.g., lime milk), or it can be directly added in dry powder form into the ball mill or stirring tank.
Saponification: For fatty acid collectors, saponification is the most common method. For example, when selecting hematite, saponified soap of paraffin and tar oil is used as a collector. To saponify tar oil, about 10% sodium carbonate should be added when preparing the reagent, and heated to create a hot soap solution for addition.
Emulsification: Emulsification can be achieved using ultrasonic emulsification or mechanical stirring. After emulsification, fatty acids and diesel can enhance their dispersion in the slurry, improving the effectiveness of the reagents. Adding some emulsifying agents can further enhance the effectiveness.
Acidification: When using cationic collectors, due to their poor solubility, they must be pre-treated with hydrochloric acid or acetic acid before they can dissolve in water for flotation.
Aerosol method: This is a new preparation method that enhances the action of reagents. It involves using a special spraying device to aerosolize the reagents in an air medium before directly adding them to the flotation tank, hence also referred to as "aerosol flotation method." This method not only improves the floatability of useful minerals but also significantly reduces reagent usage. For instance, the dosage of collectors can be only one-third to one-fourth of the usual amount, while frother dosage can be only one-fifth.
Electrochemical treatment of reagents: Direct current is passed through the solution to chemically treat flotation reagents, which can alter the reagent's state, pH value, and redox potential, thereby increasing the concentration of the most activating reagent components, raising the critical concentration for forming colloids, and improving the dispersion of poorly soluble reagents in water.
Generally, collectors and frothers are stirred for 1-2 minutes, while some reagents, like potassium dichromate used to suppress lead in copper-lead separation, may require longer stirring.
Reagent Addition Location
To maximize the effectiveness of flotation reagents, the general practice is to add adjusting agents, inhibitors, and some collectors (e.g., kerosene) in the ball mill to create a suitable flotation environment as early as possible. Collectors and frothers are mostly added in the first stirring tank of the flotation process. If there are two stirring tanks, the activator should be added in the first tank, while the collector and frother should be added in the second tank. The addition points vary based on the roles of the reagents in the flotation machine. For example, copper sulfate, yellow medicine, and pine oil are generally added in the following order: copper sulfate is added in the center of the first stirring tank, yellow medicine in the center of the second tank, and pine oil at the outlet of the second stirring tank. In general, flotation plants first add pH adjusters to bring the slurry to an appropriate pH before allowing the collector and inhibitor to work more effectively. When adding reagents, it is essential to be aware of the issue of certain harmful ions causing reagent inefficiency. For example, copper ions reacting with hydride ions can lead to the inefficiency of hydrides. In copper-sulfur separation, if there are many copper ions in the stirring tank, cyanide should not be added to the stirring tank but should be directly added during the separation flotation process.
Reagent Addition Order
The typical order of reagent addition in flotation plants is as follows: for the flotation of raw ores, it should be pH adjusters, inhibitors or activators, frothers, and collectors; for minerals that have been inhibited during flotation, the order is activators, collectors, and frothers.
Reagent Addition Methods
There are generally two methods for adding reagents: centralized addition and dispersed addition. The choice of addition method should consider both the reagent types and the reagents’ actions.
1. Centralized Addition: Most reagents are added centrally; for example, collectors, activators, and inhibitors are added to the stirring tanks.
2. Dispersed Addition: Some reagents can be added directly into the flotation tank, which is often applied to reagents that are volatile or sensitive to other reagents. For example, if the flotation reagents cause detrimental effects on one another (e.g., the negative influence of excess sodium sulfide on activated flotation), reagents can be directly added into the flotation machine.
Conclusion
Through the correct selection, preparation, dosage, and addition of flotation reagents, mineral processing and geological analysis can be optimized, enhancing the accuracy and efficiency of tests and analyses. These operational tips aim to aid laboratory technicians and mining engineers in better utilizing flotation reagents, leading to improved operational efficiency and more reliable results.
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