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Adjustment of Flotation Slurry: Water Quality

Published time:06 January 2022

The adjustment of flotation pulp includes pulp depth, PH value, and so on. The temperature and water quality of the flotation slurry have obvious effects on the separation. Before the ore pulp enters the flotation machine, if it is reasonably adjusted, the flotation machine can fully play its role and get a better flotation effect. Today we will discuss the water quality during the flotation.

Water Quality

Flotation must be carried out in an aqueous medium. The water contains various gases, ions, and some organic flotation reagents, all of which can affect the flotation process. The composition of water in different regions is very different. Therefore, the water quality must be adequately adjusted so that the flotation process can be properly adjusted.

Water Quality Standard

Both industrial water and domestic water have hard water and soft water. The hardness of water reflects the content of calcium and magnesium ions in the water. The greater the hardness of water, the more calcium and magnesium ions are contained.

Different countries have different hardness calculation standards, such as German hardness, American hardness, French hardness, British hardness, etc., and the use of millimeter equivalent hardness, 1-milligram equivalent hardness is equivalent to 20 mg of calcium ions in 1L of water, or 12.16 mg of magnesium ion. After changing the film, 1-milligram equivalent hardness = 2.804 German hardness = 50.045 American hardness = 5 French hardness. See the table below for the soft stem grade of water

 

Type of WaterHardness
Milligram Equivalent(/L)German Hardness
Very Soft Water<1.5<4.2
Soft Water1.5-3.04.2-8.4
Mouth Hardness3.0-6.08.4-16.8
Hard Water6.0-9.016.8-25
Very Hard Water>9.0>25.2

 

The hardness of water has an obvious influence on the flotation index, especially when using fatty acid collectors for flotation, its influence must be eliminated before flotation.

The problem of various ions, molecules, and compounds contained in the water is called the total mineralization of water, also known as the degree of salinity, expressed in [g/L]. The degree of salinity indicates the degree of mineralization of water, that is, the amount of salt in the water. The higher the degree of salinity of water, the higher the salt content in the water and the more polyvalent metal ions. Some of these ions are beneficial to flotation, and some are harmful; they have different effects on different minerals. Therefore, the ingredients used in flotation should be fully understood to facilitate the adjustment of the flotation process and improve the flotation effect.

 

coal floatation

The Water of Rivers and Lakes

The water of rivers and lakes is one of the most used waters for flotation. Most of them are soft water with low salinity. Except for the Great Salt Lake, for example, Lake Laurent is only 0.3048g/L and Lake Baikal is 0.069g/L. Naxi Lake 0.1511g/L. The salt content is low, and the polyvalent metal ions are relatively small. In flotation, the water factor has the least influence on the separation effect, and it is easy to perform and adjust.

Groundwater

Groundwater is also one of the most used waters in flotation. Water in different regions has great changes in water quality, and there are great differences in hardness and salinity. Soft water with low salinity and less hardness, like water in rivers and lakes, has little effect on flotation and is easy to operate and control in flotation.

As the degree of salinity increases, the hardness increases, and the content of various ions in the water increases, and the impact on the flotation effect is also significantly increased. , Magnesium plasma not only increases the consumption of collectors, but also often destroys the selectivity of the flotation process. For example, during the flotation of iron ore, calcium ions will activate quartz and silicate gangue; iron ions have an inhibitory effect on the flotation of sulfide minerals; copper ions can have an activating effect, and alkali metal ions generally have no effect on flotation.

Since the ions in the water have a significant impact on the flotation index, the harmful effects must be eliminated before flotation. Elimination methods include chemical and physical methods. The chemical method adopts the addition of certain agents to cause insoluble precipitation of harmful metals, such as sodium carbonate, reversible sodium, and other agents, which can be used. The Donganshan Concentrator adds 1.5-2.0kg/t of sodium carbonate to the grinding back to reduce the hardness of the water from the original 12 degrees to 7-8 degrees. The ion exchange method can also be used, which is more adaptable and can be used. According to needs, choose different types of exchange resins to achieve the required purpose.

Physical methods can use ultrasonic, electromagnetic treatment, etc. to achieve the purpose of eliminating harmful ions.

Saltwater

Seawater and some lake waters have higher salinity, so the salinity is also higher. For example, the Epekun Lagoon (seawater) is 375.1g/L, which is salty water. The use of saltwater for flotation is of great significance for coastal mines or salty lake areas. Flotation tests have been carried out on some minerals in salty water, and their effects are different. For example, a coal mine water contains Na+1789.6mg/L, Cl-2141.3mg/L, Mg2+28.4mg/L, SO42- 131.6mg/L, used for flotation of slime, can get a very solitary index without adding flotation agent, and the flotation speed is 60% higher than ordinary freshwater.

The use of seawater for flotation of a lead-zinc ore has a certain impact, increasing the amount of lime, copper sulfate, and other reagents, and also improving the floatablity of the gangue. In flotation, it is necessary to add water glass to suppress the gangue. The grade and recovery rate of zinc concentrate is slightly lower than the flotation index of freshwater. Because of the high salt content of saltwater, it has a certain corrosive effect on the equipment, so protection should be paid attention to.

Backwater

The backwater is the water that is returned to reuse after the tailings of the beneficiation plant is treated, and is called circulating water in the coal preparation plant. Due to the serious shortage of water resources and the requirements of environmental protection, it is necessary to return the wastewater from the orderly plant to use, and it has received more and more attention. Flotation backwater has two characteristics:

(1) Containing a lot of flotation reagents, the composition is more complicated. The reagents in the backwater are sometimes 50-100 times higher than the freshwater. When using them, you must consider their impact on the flotation process. Improper use can affect the sorting. Effect; used properly, can save medicine. The practice has proved that in the flotation of single metal ore, there are few types of reagents and single effect, so the use of backwater is relatively simple, and all backwater can be used. For example, in the flotation of copper, nickel, and sulfur, the collector xanthate is reduced by 23% and the amount of sodium hydroxide is reduced by 17% in the water.

When sorting polymetallic ore, there are many kinds of chemicals used, inhibition, activation, etc., and the recycling of backwater is compared, and the process of mixed flotation and mixed concentrate re-separation can make the use of backwater easier. For example, in lead-zinc mixed flotation, the mixed concentrate stream and mineral water can be returned to the front of the process for use. When the situation is more complicated, in principle, it is more appropriate for the wastewater discharged from the same circuit to return to the same circuit, but the pipeline and process are more complicated. Under this kind of sentiment, the plan and proportion of the use of backwater recycling should be determined through experiments.

(2) Containing a lot of solid matter, especially fine mud, solid matter in the backwater, with fine particle size, low grade or high ash content, it is easy to cover the surface of the coarse-grained concentrate when it is recycled, and the flotation effect is serious. Generally, the solid content in the still water of beneficiation should not exceed 0.2-0.3g/L. Eliminate the solid matter in the backwater, use natural clarification or add a coagulant to make it drop. Coagulants include lime, lime, and ferrous sulfate or aluminum sulfate. In order to eliminate calcium ions, aluminum sulfate can also be used as a coagulant. Polyacrylamide is often added to flocculate solid particles in the treatment of coal preparation plant tailings.

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