Mineral flotation method by adding sodium sulfide

Abstract

The invention discloses a flotation method for minerals added with sodium sulfide, and belongs to the technical field of mineral processing. According to the method, before and in the flotation operation of adding sodium sulfide, the pH value of ore pulp is controlled to be 9-12, the temperature of the ore pulp is controlled to be 20-45 DEG C, the concentration of the ore pulp is controlled to be 25-35% of the solid weight concentration, and the mineral granularity reaches the target mineral monomer dissociation degree of 85% or above; in the flotation operation section, inert gas is filled into the flotation machine to reduce the content of oxygen in the flotation area, a low-oxygen and stable operation environment is created, invalid consumption of sodium sulfide is reduced fundamentally, the effective utilization rate of sodium sulfide is remarkably increased, and therefore on the premise that the same inhibition or vulcanization effect is achieved, the use amount of sodium sulfide can be stably reduced by 20%-40%; the method is suitable for various flotation processes using sodium sulfide, and the cost reduction, efficiency improvement and environmental protection significance are remarkable.

Description

Technical Field

[0001] This invention relates to the field of mineral processing technology, and in particular to a mineral flotation method using sodium sulfide. Background Technology

[0002] Sodium sulfide (Na₂S) is an important modifier in flotation processes, widely used in two aspects: first, as a depressant in the separation of polymetallic sulfide ores (such as sphalerite and pyrite); and second, as an activator or sulfiding agent in the flotation of oxide or secondary sulfide ores, forming a sulfide film on their surface, thus enabling them to be collected by xanthate collectors. However, sodium sulfide is chemically reactive, resulting in significant ineffective consumption in flotation systems, leading to its often very high dosage, increasing beneficiation costs and environmental impact.

[0003] The main reasons for excessive sodium sulfide consumption include: oxidative decomposition, where the oxygen in the air introduced into the flotation machine oxidizes the sodium sulfide, producing ineffective components such as sodium thiosulfate and sodium sulfate. This process consumes a large amount of sodium sulfide that would otherwise be used for its intended purpose. "Quenching" reaction: certain ions in the pulp (such as Cu) 2+ Fe 3+ ) or minerals will be associated with S 2- A reaction occurs, forming a sparingly soluble sulfide precipitate, causing sodium sulfide to be "quenched" and rendered ineffective. Hydrolysis and pH fluctuations: Sodium sulfide is a strong base-weak acid salt, and its hydrolysis is significantly affected by pH (S0). 2- +H2O HS - + OH - ;HS - + H2O H2S + OH - An unsuitable pH value can alter its hydrolysis products (HS). - S 2- The pH ratio (H2S) affects the efficiency and selectivity of sodium sulfide in the inhibition or sulfidation process; excessively low pH can lead to the generation of highly toxic and volatile H2S gas, causing efficacy loss and safety issues. Temperature and slurry properties also play a role: excessively low temperatures slow down the reaction rate between sodium sulfide and the mineral surface; excessively high temperatures accelerate its oxidation and decomposition. Inappropriate slurry concentration and fineness can affect the uniformity of sodium sulfide dispersion and its contact efficiency with the mineral surface.

[0004] Currently, methods for reducing sodium sulfide usage in flotation processes mostly involve staged addition or combination with other reagents. For example, patent CN107626441B, "Method for Beneficiating Copper from Copper Smelting Slag and Beneficiation Reagents," discloses beneficiation reagents based on Na2S or NaHS, with modifiers added to improve the stability and activity of Na2S or NaHS. Patent CN107486338B, "A High-Efficiency Flotation Process for Recovering Complex Copper Oxides," discloses a flotation process for recovering complex copper oxide ores where all cleaning and scavenging processes employ staged reagent addition and rapid flotation, which can reduce the impact of slime, prevent sodium sulfide from becoming inactive, and maximize the recovery of copper oxide ores. However, these methods fail to fundamentally solve the high consumption problem caused by sodium sulfide's inherent chemical instability. Therefore, there is an urgent need for a method that can systematically protect sodium sulfide and extend its effective action time. Summary of the Invention

[0005] This invention addresses the problem of low efficacy of sodium sulfide reagents in mineral flotation processes in existing technologies by proposing a mineral flotation method that adds sodium sulfide. Before and during the flotation operation, the physicochemical parameters of the flotation environment and pulp are optimized to reduce the ineffective decomposition of sodium sulfide and thus reduce the amount of sodium sulfide used.

[0006] To achieve the above-mentioned objectives, the following technical solution is provided: This invention provides a mineral flotation method with added sodium sulfide. Before and during the flotation operation with added sodium sulfide, the pH of the flotation pulp is controlled to be 9-12, the pulp temperature to be 20-45°C, the pulp concentration to be 25-35% by weight of solids, and the mineral particle size to achieve a liberation degree of more than 85% for the target mineral. In the flotation operation section with added sodium sulfide, inert gas is introduced into the aeration device of the flotation machine to replace the air in the gas phase medium in the flotation machine with inert gas, or the inert gas is mixed with air to reduce the oxygen content in the flotation zone and achieve mineral flotation.

[0007] Furthermore, by adding lime to the slurry as a pH adjuster, the pH value is controlled at 10-12 when sodium sulfide is added before and during the flotation operation as an inhibitor; and at 9-10.5 when sodium sulfide is used as a sulfiding agent.

[0008] Furthermore, in the cold season, the slurry is preheated to above 20°C by steam heating or by utilizing the residual heat from previous operations; in the hot season, the slurry temperature is controlled below 45°C by adding cold water.

[0009] Furthermore, the concentration and fineness of the slurry are adjusted by regulating the grinding and classification operations and the amount of water added, thereby controlling the concentration and particle size composition of the slurry entering the flotation operation; the concentration is controlled by the linkage between the flow meter and the concentration meter, and the fineness is guided by periodic particle size detection to guide the grinding operation.

[0010] Furthermore, when inert gas is introduced into the flotation machine and mixed with air, the volume of inert gas accounts for no less than 80% of the gas phase composition in the flotation machine; the inert gas is either nitrogen or argon.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The mineral flotation method with added sodium sulfide proposed in this invention reduces the oxygen content in the flotation zone by introducing inert gas into the aeration device of the flotation machine, fundamentally preventing the oxidation and decomposition of sodium sulfide, thus allowing the added sodium sulfide to remain as sodium for a longer period of time. 2- or HS - The effective form exists in the slurry, giving it more opportunities to act on the surface of the target mineral, reducing its oxidation, and thus greatly improving its utilization rate.

[0012] 2. Controlling the pH, temperature, and concentration of the pulp before and during flotation effectively inhibits the ineffective decomposition of sodium sulfide. Maintaining the pulp pH between 9 and 12 ensures that sodium sulfide primarily decomposes into H₂S. - or S 2- The sodium sulfide exists in a specific form, and a high pH value can effectively inhibit the generation of highly toxic H2S gas, reducing reagent volatilization and ensuring operational safety. The temperature of the slurry, between 20 and 45°C, represents the equilibrium point for reaction kinetics and chemical stability. Temperatures above 20°C ensure the diffusion rate of sodium sulfide molecules and ions, as well as their chemical reaction rate with the mineral surface, avoiding slow reactions and delayed efficacy due to excessively low temperatures. Temperatures below 45°C effectively inhibit the rate of thermally induced decomposition and oxidation side reactions of sodium sulfide, preventing rapid deterioration at high temperatures. The slurry concentration should be controlled at 25-35% solids by weight, and the target mineral particle size should meet the requirement of a monomer dissociation degree of over 85%. This ensures that sodium sulfide can fully and uniformly contact the mineral particles. Appropriate concentration avoids uneven reagent dispersion due to excessively thin slurry or hindered reagent delivery due to excessively concentrated slurry. Appropriate fineness ensures full exposure of the target mineral surface, reducing reagent loss due to ineffective adsorption by slime or inclusions.

[0013] 3. The mineral flotation method with added sodium sulfide proposed in this invention optimizes the flotation process from three levels: "inhibiting decomposition," "optimizing morphology," and "promoting reaction," by controlling the pH, temperature, and concentration of the pulp before and during flotation, and by reducing the oxygen content in the flotation zone. This enhances the efficacy of sodium sulfide and reduces its dosage. Industrial practice shows that, under the premise of achieving the same technical indicators (inhibition effect or sulfidation effect), the flotation method proposed in this invention can stably reduce the dosage of sodium sulfide by 20-40%, resulting in significant economic and environmental benefits. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0015] Unless otherwise specified, all raw materials used in the following examples were purchased commercially.

[0016] Unless otherwise specified, the methods used in the following embodiments are conventional operating methods in the art.

[0017] In this embodiment of the invention, the step of introducing inert gas is to introduce nitrogen gas after liquid nitrogen vaporization or bottled argon gas into the gas charging device of the flotation machine, and to replace the gaseous medium in the flotation machine with inert gas by adjusting the valve, or to mix inert gas with air according to the proportion of inert gas exceeding 80%.

[0018] In this embodiment of the invention, before and during the flotation operation with added sodium sulfide, the pH value, temperature, concentration and fineness of the slurry are monitored and precisely adjusted in real time by online detection instruments and DCS automatic control system. Example 1 This embodiment describes copper ore flotation, using sodium sulfide as an activator. The minerals are a mixture of oxidized copper ore and secondary copper sulfide ore, with malachite and chalcocite being the main copper minerals. Sodium sulfide is used to sulfide the minerals, forming a thin film of copper sulfide on their surface, which can then be collected using xanthate to achieve mineral flotation. The specific method is as follows: The minerals are ground to -200 mesh using a ball mill to achieve a particle size of 90%. During slurry preparation, lime is added through an automatic lime addition system to stabilize the pH value of the feed slurry at 9.0±0.5. Water is added to the mixing tank to make the concentration of the feed slurry 30%. Nitrogen gas is introduced into the sodium sulfide mixing tank and flotation machine to replace 90% of the air, reducing the oxygen content in the flotation zone. A steam coil preheating device is added to the mixing tank to maintain the slurry temperature stably at 30±2℃. Sodium sulfide is added during roughing and scavenging for activation to achieve mineral flotation.

[0019] In this embodiment, the amount of sodium sulfide used is reduced to 180 g / t of raw ore, the copper flotation recovery rate is steadily increased to over 87%, and the fluctuation index is reduced. Due to the stable pH and temperature, the amount of H2S gas escaping is reduced, and the safety of the working environment is improved.

[0020] Example 2 This embodiment describes the separation of copper-molybdenum mixed concentrates. A combination of reagents, including sodium sulfide, is used to suppress sulfide minerals such as chalcopyrite and pyrite, allowing molybdenite (which has good natural floatability) to float and thus achieve copper-molybdenum separation. The specific method is as follows: The minerals were ground to -200 mesh using a ball mill, achieving a particle size of 90%. During slurry preparation, lime or sodium hydroxide was added via an automatic addition system to stabilize the pH of the feed slurry at 11.0±0.5. Water was added to the mixing tank to achieve a slurry concentration of 25%. Nitrogen was introduced into the sulfidation mixing tank to replace all air, and a steam coil preheating device was added to the mixing tank to lower and stabilize the slurry temperature at 40±2℃. Argon was introduced into the flotation machine, filling the entire copper-molybdenum separation circuit with argon. Sodium sulfide was added at each stage of flotation. The introduction of inert gas and the reduction of slurry temperature in the flotation section effectively suppressed the high-temperature rapid decomposition and thermal decomposition process of sodium sulfide. In this embodiment, the molybdenum recovery rate increased due to the improved separation selectivity. With the improvement of molybdenum concentrate grade, the sodium sulfide dosage was reduced from 8000g / t to 5500g / t.

[0021] Example 3 In this embodiment of lead-zinc ore flotation, sodium sulfide is used as a depressant. After flotation of galena, the zinc-sulfur mixed concentrate is separated, pyrite is suppressed, and zinc concentrate is flotated. The specific method is as follows: The minerals are ground to -200 mesh (88%) using a ball mill. Before and during flotation, the pH of the feed slurry is stably controlled at 11.2±0.2 using an automatic lime addition system. Water is added to the mixing tank to make the feed slurry concentration 28%. Nitrogen is introduced into the zinc roughing and cleaning flotation machines to replace 85% of the air. Sodium sulfide is added during the zinc flotation stage. In winter, when the temperature is too low, the feed temperature is raised using a slurry heater to maintain it at 22±2℃. In summer, when the temperature is too high, cold water is added to control the slurry temperature below 28℃, thus achieving mineral flotation.

[0022] In this embodiment, the inert gas is introduced during the flotation process to protect sodium sulfide from oxidation. The dosage is stable throughout the year, and no additional reagents are needed in winter. The average annual dosage of sodium sulfide is reduced to 1400 g / t. The grade and recovery rate of zinc concentrate are improved due to the more stable inhibition process.

[0023] Comparative Example 1 The difference between this embodiment and the flotation method in Embodiment 1 is that air is introduced into the flotation machine, sodium sulfide is added in stages, and lime is added before and during the flotation operation of adding sodium sulfide to roughly control the pH value of the pulp at 8.5-9.5. The pulp temperature varies with the environment (15-35℃) to achieve mineral flotation.

[0024] In this embodiment, the total amount of sodium sulfide used is 500g / t of raw ore, and the copper recovery rate fluctuates in the range of 80-85%.

[0025] Comparative Example 2 The difference between this embodiment and Embodiment 2 is that the flotation process in this embodiment is carried out under air, the pH value of the pulp is controlled at 11-12, and steam is used to heat the pulp to above 50°C to "enhance" the inhibition effect and achieve mineral flotation.

[0026] In this embodiment, the amount of sodium sulfide used reached 8000g / t of mixed concentrate, and the high temperature caused equipment corrosion and a harsh workshop environment.

[0027] Comparative Example 3 The difference between this embodiment and the flotation method in Embodiment 3 is that air is introduced into the flotation operation section; copper sulfate is used to activate sphalerite; lime is added to control the pH value of the pulp at around 11; the pulp temperature is the natural temperature (about 10°C in winter and about 25°C in summer); in winter, an additional amount of sodium sulfide is needed to ensure the inhibition effect; the average annual usage is about 2000 g / t of raw ore.

[0028] Compared with the mineral flotation methods of Comparative Examples 1-3, the amount of sodium sulfide used in the mineral flotation methods of Examples 1-3 of the present invention is significantly reduced, as shown in the table below, the amount of sodium sulfide used is reduced by 20-40%.

[0029]

[0030] The above-described embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above-described embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present patent shall be considered equivalent substitutions and shall be included within the protection scope of the present patent.

Claims

1. A mineral flotation method with added sodium sulfide, characterized in that: Before and during the flotation operation with added sodium sulfide, the pH of the flotation pulp is controlled at 9-12, the pulp temperature at 20-45℃, the pulp concentration at 25-35% solids weight concentration, and the mineral particle size reaches a liberation degree of over 85% for the target mineral. In the flotation section with added sodium sulfide, inert gas is introduced into the aeration device of the flotation machine to replace the air in the gas phase medium in the flotation machine with inert gas, or the inert gas is mixed with air to reduce the oxygen content in the flotation zone and achieve mineral flotation.

2. The mineral flotation method with added sodium sulfide as described in claim 1, characterized in that: The pH of the slurry is controlled at 10-12 when lime is added to the slurry as a pH adjuster, and when sodium sulfide is added before and during the flotation operation as an inhibitor; when sodium sulfide is added as a sulfiding agent, the pH of the slurry is controlled at 9-10.

5.

3. The mineral flotation method with added sodium sulfide as described in claim 1, characterized in that: In cold seasons, the slurry is preheated to above 20°C by steam heating or by utilizing the residual heat from previous operations; in hot seasons, the slurry temperature is controlled below 45°C by adding cold water.

4. The mineral flotation method with added sodium sulfide as described in claim 1, characterized in that: By adjusting the amount of water added during flotation as a pre-grinding and classification process, the concentration and particle size distribution of the pulp entering the flotation stage can be controlled.

5. The mineral flotation method with added sodium sulfide as described in claim 1, characterized in that: When an inert gas is mixed with air and filled into the flotation machine, the volume of the inert gas shall account for no less than 80% of the gas phase composition in the flotation machine; the inert gas shall be either nitrogen or argon.

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