Lime is a low-price goods, widely used in gold processing plant. It systematically expounds its related properties and its role and application in flotation, cyanidation, amalgamation and other operations for reference.
1 related properties of lime
Lime, also known as lime or white ash, has an active ingredient of CaO and is composed of limestone CaCO3 at 900~1200 °C.
It is obtained by calcination. The reaction formula is:
CaCO3→CaO + CO2↑
Lime has strong water absorption and acts as calcium hydroxide (Ca(OH)2), commonly known as slaked lime or slaked lime. It has little solubility in aqueous solution, but it can further ionize calcium ions (Ca2+) and hydroxides in aqueous solution.
The ion (OH-) makes the solution alkaline, and the reaction formula is:
CaO + H2O = Ca(OH)2 + heat
Ca(OH)2= Ca2+ + 2OH-
The slaked lime reacts with CO2 to form CaCO3. The reaction formula is:
Ca(OH)2+ CO2→ CaCO3↑ + H2O
This property is the basic reason for the formation of calcium in the bottom of mechanical equipment or in the pipeline when lime is used on site.
2 Lime in flotation and its application
Lime in the flotation process may be used to increase the pH of the slurry; thio compounds adjustment collector and other certain inhibitors (e.g., cyanide) to effect activity; useful for inhibiting flotation of iron sulfide minerals, natural gold particles Heavy metal ions that are harmful to flotation in sedimentary pulp; have the effect of agglomerating into larger aggregates.
2. 1 Adjust the pH of the slurry
Lime is cheap and easy to obtain and has a strong alkalinity. In the process of flotation of sulfide minerals, when it is necessary to increase the pH value of the slurry or need to be carried out under alkaline or weakly alkaline conditions, it is usually used as the pH value. Conditioner. In general, its role is as follows:
(1) Adjust the concentration of heavy metal ions in the slurry to form poorly soluble compounds. This is to eliminate the weight of some harmful ions
To adjust the method. For example, the addition of OH-ions can cause many metal cations to form insoluble hydroxides. The most common soluble hydroxides in flotation are: Al(OH)3, Cu(OH)2, Fe(OH)2, Fe(OH)3, Pb(OH)2, Zn(OH)2, etc. .
(2) Adjust the ion concentration of the collector. The presence of a collector in a molecular or ionic state in water is closely related to the pH of the medium. Adjusting the pH adjusts the proportion of the collector in the molecular or ionic state of the water, and actually adjusts the dissociation of the collector.
(3) Adjust the interaction between the collector and the mineral. The effect between the collector ion and the mineral surface is closely related to the pH of the slurry. The collector anion and OH- can compete on the mineral surface. The higher the pH, the greater the concentration of OH- ions. It can repel the action of the collector anion.
(4) Adjust the concentration of the inhibitor. Some inhibitors are salts composed of strong bases and weak acids. For example, the commonly used inhibitor water glass (also known as sodium silicate, whose chemical composition is NaO2SiO2) is that it can be hydrolyzed in water to make the pulp alkaline, pH value. The level directly affects its degree of hydrolysis. When pH < 9, the silicate (H2SiO3) molecule dominates; when pH = 9~13, HSiO-3 dominates; when pH > 13, SiO-3 dominates.
(5) Adjust the foaming ability of the foaming agent. The pH has an effect on the foaming ability of the foaming agent. For example, the foaming capacity of pine oil (2# oil) increases as the pH of the medium increases.
(6) Adjust the dispersion and agglomeration of the slime. The pH adjusting agent used in practice is often a dispersing agent or agglomerating agent for the slime, which acts to disperse the pulp or agglomerate the pulp. For example, Ca2+ in lime can weaken the negative charge of the quartz surface and reduce the electrostatic repulsion, which is beneficial to the adsorption of the ionic flocculant.
Gold flotation, in the treatment of ore containing simple metal sulfide ore with less cyanide harmful substances (such as most mines in Shandong), generally control the flotation pH = 7~9 with lime.
2. 2 inhibiting the flotation of iron sulfide minerals and natural gold particles
When the yellow drug-based collector is used to float various non-ferrous metal sulfide minerals (for example, flotation of copper , lead , zinc and other sulfide minerals from ore), the ore usually contains a certain amount of iron sulfide minerals, such as yellow iron. The use of lime to inhibit iron sulfide minerals is one of the main methods commonly used in production practice, such as ore, pyrite, pyrrhotite or sulfur- arsenic ore.
In the treatment of gold-containing polymetallic sulfide mineral ores with high content of valuable heavy metals (such as gold-containing polymetallic sulphide ores containing copper, copper, zinc, lead, zinc , antimony, arsenic, etc.), since these ores contain In order to eliminate unfavorable factors, in the actual production process, the flotation process combining mixed flotation and separation flotation is usually adopted, and lime is commonly used to adjust the pH value, generally controlling the mixing flotation pH=7~ 8. Allow most of the useful sulfide minerals to float up, and then use the separation flotation process to control pH = 10~12 to inhibit the separation of pyrite and achieve the purpose of separation.
Furthermore, natural gold particles are susceptible to inhibition by Ca2+. When a certain amount of lime is present in the slurry, Ca2+ reacts with CO2 in the air entering the slurry to form a CaCO3 precipitate, which inhibits the flotation of natural gold particles.
The addition of lime in the flotation operation is usually carried out by adding lime powder to the ore belt of the ball mill or adding lime milk or lime powder to the agitating tank before the flotation.
The role of lime in the flotation process is most apparently the effect on the properties of the flotation foam. When the amount of lime is appropriate, the foam formed is relatively stable and has a suitable viscosity; when the amount is large, the foam is too stable, the foam is sticky, and even causes a "running" phenomenon, making the production process difficult to operate and control. At the same time, due to the aggravation of cohesive slime, this cohesion often lacks selectivity, resulting in a large amount of ore fines in the foam concentrate, which affects the quality of the concentrate. Therefore, the amount of lime added should be strictly controlled in the flotation production of gold mines, and it should be fully recognized.
2. 3 Other functions and applications
Since lime is an inorganic electrolyte, the dissociated Ca2+ ions are adsorbed on the surface of the slime, reducing or neutralizing the negative charge on the surface of the slime, causing the fine particles to agglomerate into larger agglomerates under the action of van der Waals force, so that the actual production process Many mines use it to add to the flotation concentrate concentration thickener, accelerate the sedimentation speed of the slurry, optimize the concentration and filtration operation, and prevent the running of the concentrate.
3 The role and application of lime in cyanidation
In the cyanidation process, lime can be used as a de-agent, used in the thickening machine of the gold concentrate cyanide plant before immersion, to remove harmful substances in the cyanidation process, prevent the occurrence of gold concentrate running, and reduce unnecessary losses; As a pre-alkali dipping agent, it is used to eliminate the unfavorable factors of the leaching reaction before the leaching operation; it can be used as a protective base for the leaching process; it can be used as a regulator, used in the zinc powder replacement process, and the like.
3. 1 before cyanide leaching and its application
The role of lime before cyanide leaching comes down to three aspects. On the one hand, for gold concentrate cyanide plants, it is commonly used as a de-agent for pre-impregnation grinding classification or thickeners. By adjusting the pH value of the pulp, that is, the pH, the anion properties of the flotation reagents (such as collectors, foaming agents) are changed, and they are defeated by competition to achieve the purpose of falling off from the mineral surface. On the other hand, since it is a weak inorganic coagulant, it is used in a pre-dip thickener to eliminate the charge on the surface of the mineral, compress the electric double layer, and form fine aggregates in the slurry to form a clot and accelerate precipitation. Prevent thickeners from running and reduce unnecessary metal loss. Furthermore, by pre-dip alkali leaching (lime CaO leaching) treatment, the concentration of anion and cation in the slurry is adjusted, the leaching reaction conditions are improved, and unfavorable factors are eliminated.
In the production process, some cyanide plants use lime powder in the ball mill grading system; some add lime milk or lime powder to the sand pump box of the thickener before entering the leaching; some cyanide plants add one or two alkalis separately. The dip tank is pre-impregnated. The basic alkalinity process before the cyanidation process controls the alkalinity between 4 and 8/10,000 (calculated as CaO).
During the production process, excessive addition of lime will accelerate the sedimentation and concentration rate of the ore particles, which is not conducive to normal operation (such as thickener operation), and at the same time, CaCO3 precipitates will be blocked to block the pipeline; on the contrary, the amount of addition is insufficient, which affects both The effect of the drug does not reach the purpose of pre-alkali soaking. In short, the amount of addition is not suitable, which is not conducive to the normal cyanidation operation. Therefore, many cyanide plants do not add lime in the leaching and replacement operations without special circumstances.
3. 2 The role and application of leaching and washing operations
In order to maintain the stability of the cyanide solution and reduce the chemical loss of cyanide, an appropriate amount of alkali must be added to the cyanide solution to maintain a certain alkalinity (referred to as a protective base). Lime is usually used as this because of the nature of the lime itself. In the process of cyanide leaching and washing, the addition of lime creates favorable conditions for gold leaching and washing environment. The general effect is as follows:
(1) Prevent the hydrolysis of sodium cyanide (NaCN), reduce the concentration of HCN in the solution, and prevent the volatilization of HCN gas;
(2) Under certain conditions, the consumption of sodium cyanide by impurities can be prevented. Such as soluble copper, iron, zinc and other metal vulcanization
The leaching consumption of the material; and the combination of sulfur ions and cyanide (CN-) ions in the sulfide slurry;
(3) Neutralize the acid formed by the oxidation of CO2 and sulfide ore dissolved in water to prevent decomposition of sodium cyanide by these acids.
(4) The precipitation of the ore pellets can be accelerated during the washing process, which is beneficial to the washing operation. In the cyanide production process, especially for ores containing more sulfide components, it is usually necessary to control the concentration of lime in the leaching operation. For gold concentrate cyanide plants, the CaO concentration of the general control leaching process is between 2 and 5/10,000.
In actual production, the amount of lime should be strictly controlled. When the amount of lime is too much, the viscosity of the slurry may increase due to its flocculation, thereby increasing the resistance of solvent diffusion, causing the content of impurities in the solution to increase accordingly, forming a film of calcium peroxide on the surface of the gold particles, hindering the action of gold and sodium cyanide and oxygen. , to reduce the leaching effect; when the amount of lime is insufficient, on the one hand will increase the consumption of sodium cyanide, affecting the leaching index; on the other hand, increase the turbidity of the noble liquid, causing the washing thickener to run, affecting the subsequent zinc powder replacement operation smoothly Wait.
In the process of cyanide production, the control of lime is not emphasized, and there are many mines that cause losses. For example, in a mine in Inner Mongolia, the leaching rate of gold is reduced by 5% to 10% due to the excessive addition of lime. In another case, a certain amount of lime is added in a certain period in Shandong, and the consumption of sodium cyanide is multiplied by 4. 82kg/t. Increase to 9. 20kg / t and so on.
3. 3 The role and application of zinc powder replacement operation
In the zinc powder replacement process of the cyanide plant, it is also important to maintain the alkalinity (CaO amount) of the gold-containing liquid, ie, the precious liquid. The appropriate lime concentration can enhance the clarity of the noble liquid and improve the ion composition of the noble liquid. , changing the order of displacement reaction, affecting the rate of displacement reaction and zinc powder consumption, and thus affecting the gold substitution rate. In the replacement operation, the role of lime comes down to the following aspects:
(1) Enhance the clarity of the precious liquid and improve the quality of the gold mud. It is beneficial to the replacement operation and is beneficial to the subsequent gold smelting operation;
(2) By controlling the pH value, avoiding the formation of Zn(OH)2 and covering the zinc surface hinders the precipitation of gold. At the same time, hydrogen can be avoided in the alkaline solution to reduce the consumption of zinc powder;
(3) Change the impurity ions and their reaction state and sequence during the displacement reaction, prolong the service life of the replacement "golden cabinet" (filter press), and improve the replacement rate.
It is generally believed that when the concentration of CaO is low, impurities in the noble liquid are mainly formed by active ions, and the replacement process is mainly chemical reaction. During the high temperature season, the activity of impurity ions (such as Cu2+ ions) is enhanced, the displacement reaction is accelerated, and the product blocks the filter cloth, resulting in a decrease in the processing capacity of the "golden cabinet" and a decrease in the life. When the concentration of CaO is high, the impurities in the noble liquid are mainly in the form of compounds (such as hydroxides) and flocs (such as silica mud), and the replacement process is mainly based on physical changes. That is, when the precious liquid passes through the filter cloth of the filter press, the compound, the floc or the like forms a "film" on the surface of the filter cloth, which weakens the water permeability of the filter cloth, causes the processing capacity of the filter press to decrease, and the life of the "golden cabinet" decreases. When the CaO concentration is appropriate, the impurities in the noble solution coexist in the form of active ions and compounds. At this time, the chemical and physical changes coexist in the replacement process, and the chemical changes at this time follow the order of elemental activity.
In the production process, due to the inattention to the control of the CaO concentration in the precious liquid, the life of the "golden cabinet" is reduced, which increases the cost and enhances the labor intensity of the workers. In this respect, a mine in Shandong has a painful lesson. The mine has been released 46 times in August and September of 1989, and it has been released three times in 24 hours.
Generally speaking, for the gold concentrate zinc powder replacement cyanide plant, the CaO concentration in the noble liquid is controlled between 3 and 8/10,000 in actual production, which can meet the service life of the replacement "golden cabinet" and guarantee Zinc powder consumption and gold replacement rate ensure the quality of gold mud products. In the production process, if the amount of lime is too much, in the presence of suspended SiO2 particles and excess Pb(AC)2, colloidal calcium silicate and calcium lead chlorate will form on the zinc surface, which will deteriorate the gold. Precipitation effect. On the other hand, if the amount of lime is small, the turbidity of the noble liquid is large, which affects the quality of the gold mud. At the same time, due to the small alkalinity, zinc easily reacts to generate hydrogen to increase the consumption of zinc powder. Therefore, it is necessary to strengthen the control of lime in the zinc powder replacement operation.
4 The role and application of lime in amalgamation
(1) The effect of amalgamation is affected by adjusting the pH value. The pH of the slurry has a great influence on the effect of the mercury mixing operation. In acidic media, the surface of the base metal attached to the surface of mercury is clean and promotes the wettability of mercury to gold. However, in acidic media, the slime cannot be agglomerated. On the contrary, the contamination of gold by the slime hinders the mercury to gold. Wetting. Therefore, lime is usually used to increase the pH value of the slurry, to agglomerate the slime, and to consume the unfavorable factors that hinder the wetting of gold by the contamination of the gold particles by the slime. Usually, the pH of the amalgamation operation is 8. 0~ 8. 5.
(2) Inhibit the activity of sulfides in the slurry and prevent the mercury plate from "getting sick". Outer amalgamation operations, sometimes with sulfur or mercury sulfide powder action can mercury, to produce a black spot plate mercury, mercury loss of sheet metal capture capability, this phenomenon is particularly arsenic sulfide contained in the ore, antimony sulfide, and In particular, severe bismuth sulfide. Once this phenomenon occurs, the production of lime can be increased by increasing the amount of lime, increasing the pH of the slurry and inhibiting the activity of the sulfide.
(3) Prevent metal sulfide from adhering to the mercury plate and deteriorate the amalgamation operation. When the ore is treated with gold-containing polymetallic sulfides, metal sulfides often adhere to the mercury plate, which deteriorates the process of amalgamation. To eliminate this phenomenon, the amount of lime is often used in production, and sometimes the pH must be 12 or more. Can be solved.
(4) Elimination of magnetic amalgam in internal amalgamation operations. In the non-alkaline medium, the internal amalgamation operation sometimes produces a magnetic mercury paste, which causes the iron mineral to be mixed into the mercury paste, so that the internal mixed mercury is mostly carried out in an alkaline medium. Lime is generally used to adjust the alkalinity of the slurry, which is used in an amount of 2% to 4% of the charge.
5 other applications
Since lime absorbs mature lime Ca( OH) 2 and has a strong alkaline effect, lime has the following applications in the gold selection plant:
(1) Substituting sodium hydroxide (NaOH) as an absorbent for HCN gas in the acidification recovery process of cyanide wastewater. However, its use has great limitations, and there is no precedent in the country. It reported: Canada Flynn furlongs beneficiation plant with milk of lime, which by means of special mist of the HCN gas and the absorbent Ca (OH) 2 react to form calcium cyanide reused.
(2) Neutralization of tailings slurry or sewage acidity to prevent corrosion of equipment, pipelines, etc.
6 Conclusion
Based on a large amount of data, this paper summarizes the role and control of lime in flotation, cyanidation and amalgamation of gold mines based on the system of years of production experience. Due to the limited level, there are inevitably many shortcomings, and many criticisms and exchanges are expected. Its purpose is to inspire and attract experience.
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