Molybdenum lead ore multi-metal step-by-step leaching and extraction recovery process

Abstract

This invention relates to the field of hydrometallurgical technology and discloses a multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore. It aims to solve the problems of secondary precipitation of lead and molybdenum leading to metal loss, and severe emulsification caused by the co-leaching of impurities in existing mixed total dissolution processes. This invention mechanically activates the raw ore by introducing a grinding aid, sequentially implementing primary acidic potentiometric leaching and secondary alkaline oxidative synergistic leaching. Utilizing a specific coordination system and dual pH and potential control, it inhibits impurity dissolution and prevents lead-molybdenum interprecipitation. Subsequently, the molybdenum-rich mother liquor is acidified through a multi-stage pH gradient, combined with an amine system containing alcohol modifiers for stepwise extraction and back-extraction crystallization. This achieves highly selective sequential separation of lead and molybdenum, eliminates the third-phase emulsification phenomenon during extraction, ensures oil-water phase stability, and improves the single-metal leaching rate and product purity.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical and chemical extraction technology, and in particular to a multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore. Background Technology

[0002] Molybdenum-lead ore, as a typical polymetallic symbiotic mineral resource, possesses extremely high industrial development potential due to its rich content of high-value-added metals such as lead and molybdenum. Currently, the industry generally employs hydrometallurgical processes for the extraction of such complex symbiotic ores. Conventional existing technologies typically involve a one-step mixing and complete leaching of the crushed ore using a high-concentration strong acid or strong alkali system, followed by separation methods such as chemical precipitation or solvent extraction to attempt to individually extract different metal elements from the highly mixed and complex solution.

[0003] However, existing conventional leaching processes often face a substantial technical bottleneck: the selective separation of multiple metals is extremely difficult. Due to the significant differences in the chemical properties of lead and molybdenum, under indiscriminate and highly stimulating total dissolution conditions, the original ore structure is instantly destroyed. The large amount of released lead ions and molybdate ions readily undergo uncontrollable side reactions in the same solution system, recombine to form highly insoluble secondary precipitates such as lead molybdate, resulting in the loss of a large amount of valuable metals with the tailings. Simultaneously, this violent, non-selective reaction also promotes the co-leaching of large quantities of associated impurities such as iron, copper, and silicates from the ore. This impurity overload not only significantly reduces the extraction rate of the main metal but also greatly interferes with subsequent solvent extraction processes, easily triggering severe organic phase emulsification, causing production line shutdowns and high reagent consumption. Therefore, how to achieve efficient and highly selective sequential separation of lead and molybdenum from complex ore phase compositions, and effectively suppress the leaching of associated impurities from the source, has always been a common technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0004] Therefore, in order to solve the problems of difficulty in selective separation of multiple metals, easy side reactions of lead and molybdenum to generate secondary precipitation leading to loss of valuable metals, and serious emulsification of the organic phase in subsequent extraction caused by the co-leaching of a large amount of associated impurities in the existing conventional mixed total leaching process, this invention provides a multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] This invention provides a multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore. The raw materials include molybdenum-lead ore powder, hydrochloric acid, sodium chloride, sodium hydroxide, hydrogen peroxide, an extractant, and a diluent. The process is characterized by the following steps:

[0007] S1 ore sample pretreatment and mechanical activation: Molybdenum-lead ore is crushed, ground and mechanically activated to obtain activated ore powder;

[0008] S2 First-level acidic controlled potential selective leaching: Under acidic conditions, by controlling the redox potential and pH value, the lead element in the mineral powder is preferentially converted into complex ions and enters the liquid phase, thereby achieving selective extraction of lead;

[0009] S3 Secondary pH Gradient Adjustment and Molybdenum Oxidative Leaching: The primary leaching residue is placed in an alkaline system, and hydrogen peroxide oxidation is used in conjunction with pH gradient adjustment to dissolve molybdenum and achieve separation of molybdenum from gangue minerals.

[0010] S4 multi-stage pH gradient controlled stepwise extraction: By utilizing the difference in affinity of the extraction system under different pH conditions, the pH value of the aqueous phase is adjusted stepwise to achieve impurity removal, selective extraction of molybdenum, and recovery of residual lead in sequence.

[0011] S5 Solvent Regeneration and Product Recovery: The extracted organic phase is washed and back-extracted to obtain molybdenum and lead salt products, and the solvent and process water are recycled in a closed loop.

[0012] As a preferred embodiment of the multimetallic stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, the following raw materials are prepared in parts by weight:

[0013] 100 parts of molybdenum lead ore powder;

[0014] 15-35 parts sodium chloride;

[0015] 20-40 parts of 31wt% hydrochloric acid;

[0016] 10-25 parts sodium hydroxide;

[0017] 5-12 parts of 27.5wt% hydrogen peroxide;

[0018] Extractant P204, 2-8 parts;

[0019] Extractant N235, 5-15 parts;

[0020] Extractant: 5-15 parts of naphthenic acid or neodecanoic acid;

[0021] 0.5-2 parts of tert-decyl alcohol;

[0022] 60-120 parts of sulfonated kerosene.

[0023] As a preferred embodiment of the multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, the molybdenum-lead ore is subjected to crushing, grinding, and mechanical activation treatment to obtain activated mineral powder. The specific steps are as follows:

[0024] The particle size D90 of the molybdenum lead ore powder is ≤74μm; the mechanical activation is achieved by adding 2-5% sodium chloride by weight of the ore powder as a grinding aid in a planetary ball mill for 30-60 minutes.

[0025] As a preferred embodiment of the multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, in an acidic system, by controlling the redox potential and pH value, the lead element in the ore powder is preferentially converted into complex ions and enters the liquid phase, thereby achieving selective extraction of lead. The specific steps are as follows:

[0026] The mineral powder is mixed with a mixed acid solution consisting of hydrochloric acid and sodium chloride at a liquid-solid ratio of 4:1-6:1. The reaction temperature is controlled at 80-95℃, the pH of the system is adjusted and maintained at 1.0-1.5, and the oxidation-reduction potential is controlled at 450-500mV using a potentiometer. After reacting for 2-3 hours, the mixture is filtered while hot.

[0027] As a preferred embodiment of the multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, the primary leaching residue is placed in an alkaline system, and hydrogen peroxide oxidation combined with pH gradient adjustment is used to dissolve molybdenum, thereby achieving the separation of molybdenum from gangue minerals. The specific steps are as follows:

[0028] The primary leaching residue is added to pure water for pulping, and the liquid-solid ratio is controlled at 3:1-5:1. Hydrogen peroxide is slowly added dropwise from the high-level tank, while sodium hydroxide solution is added dropwise using an alkali feedback pump. The pH is monitored in real time using a precision pH meter, and the pH value of the system is adjusted to be constant between 9.0 and 11.0 using the alkali feedback pump. The reaction temperature is 60-80℃.

[0029] As a preferred embodiment of the multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, the process utilizes the difference in affinity of the extraction system under different pH conditions. By adjusting the pH value of the aqueous phase stepwise, impurity removal, selective extraction of molybdenum, and recovery of residual lead are achieved sequentially. The specific steps are as follows:

[0030] First-stage impurity removal extraction: Using an organic phase containing P2O4, the pH of the aqueous phase is controlled at 2.0-2.5 to extract and remove iron, copper, and zinc impurity ions;

[0031] Second-stage molybdenum extraction: Using an organic phase containing N235 and tert-decyl alcohol, the pH of the aqueous phase is adjusted to 4.5-5.5 by adding sodium hydroxide solution dropwise, so that molybdenum is extracted into the organic phase in the form of polyanions;

[0032] Third-stage lead recovery: Using macromolecular carboxylic acid extractants, the pH of the aqueous phase is adjusted to 6.0-7.0 to deeply enrich the residual lead in the remaining liquid.

[0033] In the second-stage molybdenum extraction, the organic phase consists of 10-15 vol% N235, 5-10 vol% tert-decyl alcohol and 75-85 vol% sulfonated kerosene; the volume ratio of the organic phase to the aqueous phase is controlled at 1:2-1:4.

[0034] As a preferred embodiment of the multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore described in this invention, the organic phase after extraction is washed and back-extracted to obtain molybdenum salt and lead salt products, and the solvent and process water are subjected to closed-loop circulation treatment. The specific steps are as follows:

[0035] The molybdenum-loaded organic phase was back-extracted using 10%-15wt% ammonia water. The back-extracted solution was then crystallized at a low temperature of 1-5℃ to obtain ammonium molybdate. The empty organic phase after back-extraction was washed with 1.0mol / L sulfuric acid solution and then returned to step S4 for recycling.

[0036] The pH gradient control employs a precision metering pump linked with an online pH sensor to control the pH fluctuation range ΔpH ≤ 0.2 at each stage. The secondary leaching mother liquor generated throughout the process undergoes alkali recovery via a nanofiltration membrane module, while the primary leaching mother liquor is subjected to freeze crystallization to recover sodium chloride.

[0037] The beneficial effects of this invention are:

[0038] This invention introduces a grinding aid to mechanically activate the raw ore, reducing the activation energy of the reaction. Subsequently, it sequentially performs primary acidic potentiometric leaching and secondary alkaline oxidative synergistic leaching. Utilizing a specific acid-base coordination system combined with precise pH and redox potential control, it avoids mutual interference and precipitation of lead and molybdenum from the source and effectively inhibits the excessive dissolution of impurities such as iron, copper, and silicates. After obtaining a pure molybdenum-rich mother liquor, it further employs multi-stage pH gradient precision acidification, combined with an amine extraction system containing long-chain alcohol modifiers, for stepwise impurity removal, main extraction, and back-extraction crystallization. This achieves efficient and highly selective sequential separation of lead and molybdenum, eliminates the third-phase emulsification phenomenon during extraction, ensures clear and continuous stable oil-water stratification, and improves the individual leaching rates of lead and molybdenum metals as well as the chemical purity of the final product, ammonium paramolybdate. It provides an industrially applicable closed-loop recovery technology solution. Furthermore, this invention creatively utilizes sodium chloride to achieve a synergistic effect of dual action: in the pretreatment stage, a small amount of solid sodium chloride acts as a lattice grinding aid, inducing lattice defects in molybdenum-lead ore during mechanical grinding and reducing the reaction activation energy; in the subsequent leaching stage, this portion of sodium chloride dissolves directly and, together with the sodium chloride added to the system, acts as a strong coordinating agent, providing a high concentration of chloride ions to form stable lead chloride complex ions with lead, fundamentally blocking the precipitation path of lead salts. This ingenious reagent design significantly reduces reagent consumption and simplifies the process flow. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a general flow chart of the multi-metal selective leaching and stepwise extraction and recovery process of the present invention;

[0041] Figure 2 This is a three-dimensional response surface methodology diagram illustrating the effect of pH value and ORP potential on lead leaching rate during the primary acid leaching process of this invention.

[0042] Figure 3 This is a contour plot showing the effect of the pH value of the aqueous phase and the volume ratio of the organic phase to the aqueous phase on the molybdenum extraction rate in the second-stage molybdenum extraction of this invention. Detailed Implementation

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0044] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0045] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0046] The following embodiments and comparative examples of the present invention provide a stepwise leaching and extraction recovery process for polymetallic molybdenum-lead ore, as shown below:

[0047] Example 1

[0048] Reference Figures 1-3 This is the first embodiment of the present invention, which provides a multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore, including the following steps:

[0049] Step 1: Mineral Sample Pretreatment and Mechanical Activation: Accurately weigh 1000g of dried molybdenum-lead ore powder and add 30g of industrial-grade sodium chloride powder as a grinding aid. Load the mixture into the zirconia ball mill jar of a planetary ball mill, adding zirconia grinding balls at a ball-to-material mass ratio of 4:1. Set the ball mill speed to 350 rpm and continuously mill for 45 minutes. After milling, sieve the material through a standard test sieve to ensure that the particle size distribution of the collected activated mineral powder meets the requirement of D90≤74μm. This step utilizes mechanical stress to create defects in the mineral lattice, reducing the activation energy of subsequent reactions.

[0050] Step 2, Primary Acid Potentially Controlled Selective Leaching (Main Lead Leaching): In a reactor equipped with a PTFE liner and a stirrer, prepare 5000 mL of a mixed acid leaching solution with a liquid-to-solid ratio of 5:1. The concentration of hydrochloric acid in this leaching solution is 2.0 mol / L, and the concentration of sodium chloride is 1.5 mol / L. Start the stirrer and set the speed to 400 rpm. Slowly and evenly add the activated mineral powder obtained in Step 1 into the reactor. Turn on the water bath heating and raise the temperature of the reaction system to 85°C. During the reaction, both potential and pH were controlled. Specifically, an online ORP monitoring electrode was inserted into the reaction solution, and the target potential was set to 480 mV. If the potential was too high, a very small amount of 0.1 mol / L sodium sulfite solution was automatically added; if the potential was too low, air was introduced at a rate of 0.5 L / min to ensure potential stability. Simultaneously, an online pH meter was used in conjunction with a dosing pump to strictly maintain the pH of the system at 1.2 by adding 5.0 mol / L concentrated hydrochloric acid, with fluctuations controlled within ±0.05. After 2.5 hours of constant temperature and constant potential reaction, hot filtration was immediately performed using a heat-insulating vacuum filtration device to prevent lead chloride crystallization due to cooling. The filter cake was then washed with a small amount of hot acid water at 85°C and pH 1.5, and the wash water was added to the filtrate, ultimately yielding a lead-containing leachate rich in coordinated lead ions and a primary leaching residue.

[0051] Step 3: Secondary pH Gradient Adjustment and Molybdenum Oxidation Leaching: Transfer the primary leaching residue (approximately 420g) to another reactor. Add 1680mL of pure water and slurry, maintaining a liquid-to-solid ratio of approximately 4:1. Start stirring at 300rpm and heat to 70℃. Using a metering pump, add 40mL of 27.5% hydrogen peroxide (by mass) dropwise at a flow rate of 5mL / min to oxidize and break up the low-valence encapsulations. Maintain a constant pH gradient during oxidation. Prepare a 3.0mol / L sodium hydroxide solution in a high-level tank. Set the target pH to 10.0 using a PID automatic control system. As hydrogen peroxide is added and the reaction proceeds, the PID system automatically controls the start and stop of the alkali pump to ensure that the pH fluctuation ΔpH ≤ 0.1 throughout the reaction. After 2.0 hours of reaction, filter the solution. Wash the tailings with a small amount of warm water. Combine the filtrates to obtain a molybdenum-rich solution mainly containing sodium molybdate.

[0052] Step 4, Stepwise Extraction with Multi-Stage pH Gradient Control: This step is carried out in a standard box-type mixing and clarification tank. First, a first-stage extraction is performed to remove iron and copper. After cooling the molybdenum-rich solution to room temperature, 10wt% dilute sulfuric acid is slowly added dropwise to adjust the pH of the aqueous phase to 2.2. An organic phase containing 20% ​​P2O4 and 80% sulfonated kerosene by volume is prepared and mixed at a volume ratio of 1:1 between the organic phase and the aqueous phase. The mixture is stirred vigorously for 10 minutes and allowed to stand for clarification for 15 minutes to separate the impurity-laden organic phase, yielding a pure molybdenum-containing aqueous phase. The second stage of molybdenum extraction was then performed. Sodium hydroxide solution was added dropwise to the molybdenum-containing aqueous phase to adjust its pH to 5.0, converting molybdenum into polymolybdate ions that are easily extracted by amines. A molybdenum extraction organic phase was prepared, consisting of 15% N235, 5% tert-decyl alcohol, and 80% sulfonated kerosene by volume. This organic phase was added to the aqueous phase at a volume ratio of 1:3, and the mixture was extracted for 15 minutes, followed by a 20-minute settling period to separate the phases. After separating the aqueous phase, a molybdenum-loaded organic phase was obtained. Finally, the third stage of lead recovery was performed. Sodium hydroxide solution was added dropwise to the remaining liquid to adjust the pH of the aqueous phase to 6.5. A macromolecular carboxylic acid extractant was used to deeply enrich the residual lead. The macromolecular carboxylic acid extractant was preferably naphthenic acid or neodecanoic acid, and the corresponding extraction organic phase composition was: 15% naphthenic acid or neodecanoic acid by volume, and 85% sulfonated kerosene diluent. The volume ratio of the organic phase to the aqueous phase was controlled at 1:2 during extraction.

[0053] Step 5, Post-processing and Product Crystallization: Add 12% ammonia solution to the molybdenum-loaded organic phase, maintaining a 2:1 volume ratio of organic to aqueous phase. Mix and shake for 20 minutes to transfer all molybdenum from the organic phase to the ammonia solution. After phase separation, a high-concentration ammonium molybdate solution and a washed empty organic phase are obtained and can be recycled back to Step 4. The resulting ammonium molybdate solution is concentrated to one-third of its original volume using a rotary evaporator, and then placed in a crystallizer at 2°C for 12 hours. Finally, the precipitated white crystals are filtered and dried in a vacuum oven at 60°C for 4 hours to obtain the final product. Simultaneously, the lead-loaded organic phase separated in Step 4 is back-extracted using a 1.5 mol / L dilute acid (such as hydrochloric acid or sulfuric acid). The resulting lead-rich back-extraction solution is sent to the preceding lead recovery section for crystallization to obtain the lead salt product. The empty organic phase after back-extraction is washed and returned to the third-stage extraction cycle for reuse.

[0054] Performance testing: Chemical titration and ICP-OES analysis showed that the lead leaching rate in this embodiment reached 98.8%, and the molybdenum leaching rate reached 99.2%. During each extraction stage in step four, the settling time was less than 30 seconds, the oil-water interface was clear and sharp, and no flocculent emulsification occurred. The final crystalline product was identified by XRD diffraction as high-purity ammonium paramolybdate, with a chemical purity of 99.95%, meeting the analytical purity requirements of relevant chemical industry standards.

[0055] Example 2 (Changing process parameter limits)

[0056] A multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore is disclosed. The preparation method is essentially the same as in Example 1, with the only difference being the adjustment of some process parameters. Specifically, in the first-stage acidic leaching of step two, a mixed acid leaching solution is prepared to adjust the liquid-to-solid ratio to 4:1, the heating temperature of the reaction system is reduced to 80°C, and the pH of the system is strictly maintained at 1.0 using an online pH meter during dual-control regulation. In the second-stage pH gradient regulation of step three, the target pH is set and controlled at 9.0 using a PID automatic control system. In the second-stage molybdenum main extraction of step four, sodium hydroxide solution is added dropwise to adjust the pH of the molybdenum-containing aqueous phase to 4.5, and the molybdenum extraction organic phase is added at a volume ratio of organic phase to aqueous phase of 1:2. All other raw material types, ratios, and specific operating steps remain completely consistent with Example 1.

[0057] Performance Testing: Testing in this embodiment verified the stability of the process when operating at the lower parameter limits. Although the reaction rate slowed slightly due to the reduced temperature and liquid-to-solid ratio, the final lead leaching rate still reached 97.5%, and the molybdenum leaching rate reached 98.1%. The oil-water phase remained clear during the extraction process, and the purity of the final product met the requirements.

[0058] Example 3 (Changing process parameter limits)

[0059] A multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore is disclosed. The preparation method is essentially the same as in Example 1, with the only difference being the adjustment of some process parameters. Specifically, in the first-stage acidic leaching of step two, a mixed acid leaching solution is prepared to increase the liquid-to-solid ratio to 6:1, the heating temperature of the reaction system is increased to 95°C, and the pH of the system is maintained at 1.5. In the second-stage pH gradient adjustment of step three, the target pH is set and controlled at 11.0 using a PID automatic control system. In the second-stage molybdenum main extraction of step four, sodium hydroxide solution is added dropwise to adjust the pH of the molybdenum-containing aqueous phase to 5.5, and the molybdenum extraction organic phase is added at a volume ratio of organic phase to aqueous phase of 1:4. All other raw material types, ratios, and specific operating steps remain completely consistent with Example 1.

[0060] Performance Testing: Testing in this embodiment verified the applicability of the process when operating at the upper limit of parameters. Increasing the liquid-to-solid ratio and temperature significantly improved material flowability and reaction kinetics, ultimately achieving a lead leaching rate of 98.5% and a molybdenum leaching rate of 99.0%. Simultaneously, the reduction in the organic-to-aqueous phase volume ratio to 1:4 during the extraction stage decreased the consumption of expensive organic reagents, demonstrating the extremely high industrial economic benefits of this process.

[0061] Comparative Example 1 (Changing the pH value of the first-stage leaching)

[0062] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as that in Example 1, except that in the first-stage acid leaching of step two, the pH value of the system is controlled to be increased to 3.0 when adding acid. All other operating conditions and parameters are completely consistent with those in Example 1.

[0063] Performance testing revealed that the pH of the primary leaching system was too high (3.0), falling outside the core control range of this invention. This caused the dissolved lead ions to readily hydrolyze in the solution, regenerating secondary precipitates of lead chloride or lead hydroxide. Ultimately, the lead leaching rate plummeted to 62.4%, with a large amount of unleached lead remaining in the residue, interfering with the alkaline extraction process of molybdenum in the subsequent step three.

[0064] Comparative Example 2 (ORP not controlled)

[0065] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as in Example 1, except that in the first-stage acid leaching of step two, an online ORP monitoring electrode and a dosing system are not introduced, i.e., no potential control is performed, and the system is allowed to drift naturally to a high potential state above 600mV under the influence of hydrogen peroxide and air. All other operations are consistent with those in Example 1.

[0066] Performance testing revealed that, due to the lack of suppression of the redox potential, a large amount of iron, copper, and other impurity minerals associated with the ore were excessively oxidized and dissolved into the primary leaching solution. This not only resulted in extremely high impurity levels in the lead-containing filtrate and a sharp decline in the purity of subsequent lead products, but also caused the large-scale dissolution of iron ions to overburden subsequent extraction and impurity removal processes, significantly increasing solvent consumption.

[0067] Comparative Example 3 (Inadequate pH control / excessive fluctuations in secondary leaching pH)

[0068] A leaching and recovery process for polymetallic molybdenum-lead ore is prepared in a manner that is basically the same as in Example 1. The difference is that in the secondary leaching step three, the scheme of using a high-level tank and a PID system for precise constant control is abandoned. Instead, a large amount of sodium hydroxide solution is added at once after pulping, so that the initial pH of the system instantly reaches 13.5, and the pH is allowed to drop naturally without maintenance during the subsequent 2-hour reaction process.

[0069] Performance testing revealed that the initially excessively alkaline environment caused significant erosion and dissolution of silicates and aluminates in the mineral residue. When this batch of molybdenum-rich solution entered the extraction stage in step four and sulfuric acid was added for acid adjustment, a large amount of dissolved silica underwent a condensation reaction to form a silica gel network, triggering emulsification (i.e., the formation of a third phase). This resulted in the aqueous and organic phases adhering to a paste-like consistency, making separation by settling impossible. The final molybdenum recovery rate plummeted to only 71.3%, forcing the entire extraction line to be shut down for cleaning.

[0070] Comparative Example 4 (mechanical activation without the addition of grinding aids)

[0071] A leaching and recovery process for polymetallic molybdenum-lead ore is provided. The preparation method is basically the same as that in Example 1. The difference is that in the ore sample pretreatment in step one, only 1000g of raw ore powder is subjected to conventional dry ball milling without adding sodium chloride powder as a grinding aid, thus failing to achieve effective mechanical activation.

[0072] Performance testing: The results showed that the lack of sodium chloride particles inducing mineral lattice breakage and surface defects during ball milling failed to effectively reduce the ore's activation energy (i.e., poor mineral reactivity). Under the same leaching time and temperature conditions, the lead leaching rate in step two was only 81.5%, and the molybdenum leaching rate in step three was 84.2%, demonstrating the irreplaceable role of the specific mechanical activation step in improving the overall multi-metal leaching efficiency.

[0073] Comparative Example 5 (Changing the pH of the aqueous phase in the extraction section)

[0074] A leaching and recovery process for polymetallic molybdenum-lead ore is prepared in a manner that is basically the same as in Example 1. The only difference is that in the second-stage molybdenum main extraction operation in step four, the purified aqueous phase is directly added to the extraction tank without adding sodium hydroxide solution to adjust the target pH. The aqueous phase is directly mixed with the organic phase in a slightly alkaline state with a pH of 8.0 for extraction.

[0075] Performance testing: Tests showed that under slightly alkaline conditions (pH 8.0), molybdenum in the solution mainly existed in the free form of monomolybdate ions, and the amine extractant (N235) used could not achieve effective protonation at this pH. This resulted in the organic phase being unable to adsorb molybdenum ions from the aqueous phase via anion exchange, and the actual molybdenum extraction rate decreased to less than 15%, verifying the crucial role of precisely controlling the pH of the aqueous phase within a specific acidic range for amine extraction systems.

[0076] Comparative Example 6 (Traditional Mixed Total Dissolution Method)

[0077] This comparative example aims to simulate the industry's traditional one-step strong acid complete dissolution process. The specific procedure is as follows: 1000g of conventionally pulverized molybdenum-lead ore powder is directly added to a reaction vessel, followed by the addition of a high-concentration mixture of hydrochloric acid and hydrogen peroxide. The mixture is then vigorously stirred and reacted at 90°C for 3 hours. After the reaction, the mixture is filtered while still hot, attempting to extract lead and molybdenum simultaneously.

[0078] Performance Testing: Testing revealed that under these strong acid and strong oxidizing conditions without any potential or pH gradient control, the mineral structure was rapidly destroyed, and lead and molybdenum were released simultaneously into the same solution. Due to the loss of the protective barrier of different pH ranges, high concentrations of lead ions and molybdate ions underwent uncontrollable side reactions in the solution, recombineing to form extremely insoluble lead molybdate secondary precipitate that entered the tailings. Final testing showed that the extraction rate of lead under this traditional process was only 55%, and the extraction rate of molybdenum was only 48%, and the leachate was filled with impurities such as iron and copper, making it impossible to achieve the efficient and selective separation of multiple metals as described in this invention.

[0079] Comparative Example 7 (Changing the acid system of the primary leaching)

[0080] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is essentially the same as in Example 1, except that in the primary acid leaching step two, the mixed acid leaching solution of 2.0 mol / L hydrochloric acid and 1.5 mol / L sodium chloride is replaced with a 1.0 mol / L sulfuric acid solution with an equivalent hydrogen ion concentration, meaning the system contains no chloride ions. All other operating conditions and parameters remain completely consistent with those in Example 1.

[0081] Performance testing revealed that, due to the lack of chloride ion coordination in the sulfuric acid system, lead ions dissolved by the acid combined with sulfate ions in the solution, forming a highly insoluble lead sulfate precipitate that was then reintroduced into the leaching residue. This resulted in a precipitate drop in the lead leaching rate to less than 5%, with almost no lead extraction. Simultaneously, the large amount of lead sulfate-coated slag hindered the contact between the alkali solution and the internal molybdenum elements during the alkaline leaching process in step three, causing the molybdenum extraction rate to also drop significantly to 63.5%. This comparative example demonstrates the irreplaceable role of a specific coordination system (HCl + NaCl).

[0082] Comparative Example 8 (modifier for changing the organic phase of the extract)

[0083] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as in Example 1, except that in the second-stage molybdenum main extraction in step four, the ratio of the organic phase is changed, and the long-chain alcohol modifier, tert-decyl alcohol, is removed. Only an organic phase composed of 15% N235 and 85% sulfonated kerosene by volume is used for extraction. All other operations are consistent with those in Example 1.

[0084] Performance testing revealed that during the mixed extraction process, the extractant formed by the combination of amine extractant (N235) and polymolybdate had extremely poor solubility in pure kerosene diluent. Furthermore, the lack of tert-decyl alcohol as a phase modifier to improve interfacial tension led to the rapid formation of a large amount of viscous, flocculent third phase (i.e., an emulsion layer) at the interface between the aqueous and organic phases. This resulted in severe entrainment between the oil and water phases, making complete separation by settling impossible. The effective extraction rate of molybdenum was only 42.1%, forcing the entire continuous extraction line to be interrupted for cleaning.

[0085] Comparative Example 9 (Oxidizing agent removed in secondary leaching)

[0086] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as in Example 1, except that in the secondary leaching step three, sodium hydroxide solution is added dropwise in a high-level tank to adjust and maintain the pH of the system at 10.0, and no hydrogen peroxide is added for oxidation synergy throughout the process. All other operations are consistent with those in Example 1.

[0087] Performance testing revealed that, due to the lack of deep oxidation by hydrogen peroxide, some molybdenum elements tightly bound in low-valence or isomorphous states within the minerals could not be effectively oxidized to high-valence molybdate ions and dissolved. Under the same constant temperature and pH alkaline leaching time, the final molybdenum leaching rate reached only 68.2%, demonstrating that alkaline leaching alone cannot achieve efficient extraction of bound molybdenum; synergistic alkaline leaching and deep oxidation are indispensable key steps.

[0088] Comparative Example 10 (changing the type of stripping agent)

[0089] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as that in Example 1, except that in the post-treatment step five, the stripping agent is replaced with an equivalent amount of sodium hydroxide solution instead of 12% ammonia water. All other back-extraction, evaporation, crystallization, and drying operations are completely consistent with those in Example 1.

[0090] Performance testing: While sodium hydroxide can effectively back-extract molybdenum from the organic phase, the resulting product is sodium molybdate. Due to the extremely high solubility of sodium molybdate, it is very difficult to precipitate during the subsequent 2°C freeze-crystallization process, resulting in a large amount of unrecovered molybdenum remaining in the crystallization mother liquor, with a single crystallization yield of only 45%. Furthermore, the precipitated sodium molybdate crystals readily trap impurity ions from the aqueous phase, resulting in a product chemical purity of only 92.5%, far below the 99.95% analytical purity requirement of ammonium paramolybdate in the examples, thus losing its high-value-added economic attributes.

[0091] Comparative Example 11 (Changing the physical parameters of the preprocessing)

[0092] A leaching and recovery process for polymetallic molybdenum-lead ore is disclosed. The preparation method is basically the same as in Example 1, except that the ball milling time of the planetary ball mill is shortened in the ore sample pretreatment step one, so that the particle size distribution of the activated ore powder collected by sieving is controlled only within D90≤150μm (about twice as coarse as in Example 1). The remaining chemical reagents, ratios, and leaching parameters are consistent with those in Example 1.

[0093] Performance testing revealed that the excessively large particle size of the feed mineral powder significantly reduced the specific surface area of ​​the mineral particles, resulting in insufficient effective contact area for the solid-liquid reaction. Limited by the unreacted nucleus model, the leachate struggled to penetrate deep into the particles. Within the same 2.5-hour primary leaching time and 2.0-hour secondary leaching time, the leaching rate of lead was only 73.4%, and that of molybdenum was only 76.8%. This comparative example demonstrates the importance of specific fine particle size limits for ensuring efficient multi-metal leaching reaction kinetics.

[0094] Performance Testing and Overall Evaluation

[0095] To more intuitively illustrate the technical effects of the present invention, the technical indicators obtained from Examples 1-3 and Comparative Examples 1-11 are summarized and compared.

[0096] (1) Leaching rate test: The leaching rate is calculated based on the mass conservation of lead and molybdenum elements in the raw ore and slag, combined with the detection of liquid phase metal concentration by ICP-OES spectrometer;

[0097] (2) Extraction layering state: After standing in the mixing and clarifying tank for 20 minutes, observe the clarity of the interface between the organic phase and the aqueous phase with the naked eye and assess whether a third phase (emulsion layer) is generated.

[0098] (3) Purity of final product: The chemical purity of the final precipitated ammonium molybdate crystals was determined by XRD qualitative analysis and chemical titration.

[0099] Table 1: Comparison of Comprehensive Performance Test Results of Each Embodiment and Comparative Example

[0100] Test Project Lead leaching rate (%) Molybdenum leaching rate (%) Extraction layering state Final molybdenum product purity (%) Core Defect / Notes Analysis Example 1 98.8 99.2 Clear and sharp layering 99.95 Optimal process parameters, best overall performance Example 2 97.5 98.1 Clear layering 99.91 The lower limit of the parameters indicates a slightly slower response, but the performance meets the standards. Example 3 98.5 99.0 Clear layering 99.93 High parameter limits, low drug consumption, and excellent economic efficiency. Comparative Example 1 62.4 65.2 Clear layering - The pH of the primary leaching was too high, resulting in severe lead hydrolysis and precipitation. Comparative Example 2 96.5 97.2 Clear layering ＜90.0 Uncontrolled potential led to the extensive leaching of impurities, resulting in extremely low purity. Comparative Example 3 98.8 99.2 Severe emulsification Unable to be purified Alkaline leaching caused pH loss, leading to silica gel precipitation and the collapse of the extraction system. Comparative Example 4 81.5 84.2 Clear layering 99.50 Without grinding aid activation, mineral reaction kinetics are limited. Comparative Example 5 98.8 99.2 Clear layering (Extraction rate < 15%) Without acid adjustment during extraction, amine reagents cannot adsorb molybdenum. Comparative Example 6 55.0 48.0 - - Traditional miscibility methods result in secondary precipitation of lead and molybdenum. Comparative Example 7 ＜5.0 63.5 - - By switching to a sulfuric acid system, the lead completely precipitates without the coordination of chloride. Comparative Example 8 98.8 99.2 Severe emulsification (Extraction rate 45%) The lack of alcohol modifiers leads to poor solubility of the organic phase and the formation of a third phase. Comparative Example 9 98.8 68.2 Clear layering 99.85 Without hydrogen peroxide synergy, encapsulated low-valence molybdenum cannot dissolve. Comparative Example 10 98.8 99.2 Clear layering 92.50 The products from alkaline back-extraction have high solubility but low crystallization rate / purity. Comparative Example 11 73.4 76.8 Clear layering 99.88 Excessively large particle size and insufficient specific surface area result in low leaching rate.

[0101] Comprehensive analysis and determination of the final optimal solution

[0102] Based on the above embodiments and comparative experiments, the present invention will now conduct a comprehensive analysis and weighing of all experimental results, and finally determine the preferred technical solution of the present invention.

[0103] I. Comprehensive Analysis

[0104] The core of this invention lies in solving the technical bottlenecks of difficult lead-molybdenum separation, high impurity leaching rate, and easy emulsification of organic phase in traditional molybdenum-lead ore processing by precisely controlling multi-level pH gradients, introducing specific coordination and oxidation systems, and optimizing solvent extraction formulations.

[0105] 1. Synergistic effect analysis of leaching system and parameters:

[0106] Primary acidic coordination leaching (Comparative Examples 1, 2, and 7): Data confirms that using a specific HCl-NaCl mixed acid system (Comparative Example 7 demonstrates that a sulfuric acid system leads to complete lead precipitation), controlling the system pH at 1.0-1.5 (Comparative Example 1 demonstrates that excessively high pH leads to lead hydrolysis), and simultaneously controlling the redox potential at 450-500mV (Comparative Example 2 demonstrates that uncontrolled potential leads to the dissolution of large amounts of impurities such as iron and copper), is a necessary prerequisite for achieving highly selective lead separation and avoiding impurity overload in subsequent processes.

[0107] Secondary alkaline oxidative leaching (Comparative Examples 3 and 9): The results showed that simultaneous addition of hydrogen peroxide for oxidation during alkaline leaching (Comparative Example 9 confirmed that the absence of oxidant would prevent the encapsulated molybdenum from dissolving) and precise control of pH between 9.0 and 11.0 using PID linkage is the optimal technical window to ensure efficient extraction of molybdenum and effectively inhibit silicate dissolution (Comparative Example 3 confirmed that excessively high pH would induce severe subsequent emulsification).

[0108] Mechanical activation kinetics (Comparative Examples 4 and 11): Experiments show that adding grinding aids and conducting high-energy mechanical activation at a particle size critical value of D90≤74μm can reduce the reaction activation energy, which is a key physical factor to ensure a high leaching rate of over 98% in a short time.

[0109] 2. Analysis of the decisive role of extraction and crystallization processes:

[0110] Multi-stage pH gradient extraction (Comparative Examples 5 and 6): The "one-step" total dissolution process in Comparative Example 6 resulted in mutual interference between lead and molybdenum, proving that the "stepwise leaching followed by stepwise extraction" method in this process can avoid mutual interference in the extraction of valuable metals. Meanwhile, Comparative Example 5 shows that the pH of the aqueous phase must be precisely adjusted to a specific acidic range (4.5-5.5) using sodium hydroxide solution to trigger the efficient adsorption of polymolybdate by the amine extractant (N235). A slightly alkaline environment will cause the extraction system to completely fail.

[0111] Organic phase ratio and back-extraction selection (Comparative Examples 8 and 10): Data confirms that adding long-chain alcohols (such as tert-decyl alcohol) as phase modifiers to the organic phase is the core technical guarantee for eliminating the third phase and avoiding extraction emulsification (Comparative Example 8); while using ammonia instead of sodium hydroxide in the back-extraction process (Comparative Example 10) is the decisive step in finally obtaining a high crystallization yield and high value-added analytical grade product (ammonium molybdate).

[0112] II. Determination of the Optimal Solution

[0113] Based on the above analysis, a preferred technical solution (i.e., the best implementation method) of the present invention is as follows:

[0114] 1. Optimize key process parameters:

[0115] Pretreatment: The particle size of the mineral powder is D90≤74μm; add 3% NaCl by weight of the mineral powder for mechanical activation.

[0116] First-stage lead immersion: liquid-to-solid ratio 5:1, temperature 85℃, reaction time 2.5 hours; system pH is kept constant at 1.2, and ORP potential is kept constant at 480mV.

[0117] Secondary molybdenum immersion: liquid-to-solid ratio 4:1, temperature 70℃, hydrogen peroxide added dropwise for 2.0 hours; system pH is controlled at 10.0 by PID control.

[0118] Optimal extraction system: 15 vol% N235 + 5 vol% tert-decyl alcohol + 80 vol% sulfonated kerosene was used as the organic phase for molybdenum extraction; the pH of the aqueous phase was controlled at 5.0, and the volume ratio of the organic phase to the aqueous phase was 1:3.

[0119] 2. Optimal Process Flow Summary:

[0120] The activated mineral powder is first subjected to primary acid leaching under constant low pH and controlled potential to achieve selective extraction of lead; the resulting leaching residue is subjected to secondary alkaline leaching under precise high pH and synergistic oxidation to achieve efficient release of molybdenum; after the molybdenum-rich mother liquor is acidified and impurities removed, it is subjected to primary extraction using an amine organic phase with a specific pH gradient; finally, ammonium molybdate product is obtained by ammonia back-extraction and low-temperature crystallization.

[0121] The extraction process operated by this preferred scheme (i.e. Example 1) has achieved excellent overall performance in terms of lead / molybdenum leaching rate (both > 98.5%), extraction layering stability (completely non-emulsified), and final product purity (99.95% ammonium molybdate), overcoming the inherent problems of traditional processes.

[0122] In summary, this invention reduces the activation energy of the reaction by introducing a grinding aid to mechanically activate the raw ore. Subsequently, it sequentially performs primary acidic potentiometric leaching and secondary alkaline oxidative synergistic leaching. Utilizing a specific acid-base coordination system combined with precise pH and redox potential control, it avoids mutual interference and precipitation between lead and molybdenum from the source and effectively inhibits the excessive dissolution of impurities such as iron, copper, and silicates. After obtaining a pure molybdenum-rich mother liquor, it further employs multi-stage pH gradient precision acidification, combined with an amine extraction system containing long-chain alcohol modifiers, to perform stepwise impurity removal, main extraction, and back-extraction crystallization. This achieves efficient and highly selective sequential separation of lead and molybdenum, eliminates the third-phase emulsification phenomenon during extraction, ensures clear and continuous stable oil-water stratification, and improves the individual leaching rates of lead and molybdenum metals as well as the chemical purity of the final product, ammonium paramolybdate. It provides an industrially applicable closed-loop recovery technology solution.

[0123] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore, the raw materials of which include molybdenum-lead ore powder, hydrochloric acid, sodium chloride, sodium hydroxide, hydrogen peroxide, extractant, and diluent, characterized in that, Includes the following steps: S1 ore sample pretreatment and mechanical activation: Molybdenum-lead ore is crushed, ground and mechanically activated to obtain activated ore powder; S2 First-level acidic controlled potential selective leaching: Under acidic conditions, by controlling the redox potential and pH value, the lead element in the mineral powder is preferentially converted into complex ions and enters the liquid phase, thereby achieving selective extraction of lead; S3 Secondary pH Gradient Adjustment and Molybdenum Oxidative Leaching: The primary leaching residue is placed in an alkaline system, and hydrogen peroxide oxidation is used in conjunction with pH gradient adjustment to dissolve molybdenum and achieve separation of molybdenum from gangue minerals. S4 multi-stage pH gradient controlled stepwise extraction: By utilizing the difference in affinity of the extraction system under different pH conditions, the pH value of the aqueous phase is adjusted stepwise to achieve impurity removal, selective extraction of molybdenum, and recovery of residual lead in sequence. S5 Solvent Regeneration and Product Recovery: The extracted organic phase is washed and back-extracted to obtain molybdenum and lead salt products, and the solvent and process water are recycled in a closed loop.

2. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, Prepare the following raw materials by weight: 100 parts of molybdenum lead ore powder; 15-35 parts sodium chloride; 20-40 parts of 31wt% hydrochloric acid; 10-25 parts sodium hydroxide; 5-12 parts of 27.5wt% hydrogen peroxide; Extractant P204, 2-8 parts; Extractant N235, 5-15 parts; Extractant: 5-15 parts of naphthenic acid or neodecanoic acid; 0.5-2 parts of tert-decyl alcohol; 60-120 parts of sulfonated kerosene.

3. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, In step S1, the particle size D90 of the molybdenum lead ore powder is ≤74μm; the mechanical activation involves adding sodium chloride at 2-5% of the weight of the ore powder as a grinding aid in a planetary ball mill for 30-60 minutes.

4. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, Step S2 specifically includes: mixing mineral powder with a mixed acid solution composed of hydrochloric acid and sodium chloride at a liquid-solid ratio of 4:1-6:1, controlling the reaction temperature at 80-95℃, adjusting and maintaining the pH of the system at 1.0-1.5, and simultaneously using a potentiometer to control the oxidation-reduction potential at 450-500mV, and filtering while hot after reacting for 2-3 hours.

5. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, Step S3 specifically includes: adding the primary leaching residue to pure water for pulping, controlling the liquid-solid ratio to be 3:1-5:1, slowly adding hydrogen peroxide by turning on the high-level tank, and simultaneously adding sodium hydroxide solution by using an alkali feedback pump. The pH value of the system is monitored in real time by a precision pH meter and adjusted to be constant between 9.0 and 11.0 by using the alkali feedback pump. The reaction temperature is 60-80℃.

6. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, The multi-level process in step S4 The specific process parameters for gradient-controlled stepwise extraction are as follows: First-stage impurity removal extraction: Using an organic phase containing P2O4, the pH of the aqueous phase is controlled at 2.0-2.5 to extract and remove iron, copper, and zinc impurity ions; Second-stage molybdenum extraction: An organic phase containing N235 and tert-decyl alcohol is used, and the aqueous phase is adjusted by adding sodium hydroxide solution dropwise. At a temperature of 4.5-5.5, molybdenum is extracted into the organic phase in the form of polyanions; Third-stage lead recovery: Using macromolecular carboxylic acid extractants, the pH of the aqueous phase is adjusted to 6.0-7.0 to deeply enrich the residual lead in the remaining liquid.

7. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 6, characterized in that, In the second stage of molybdenum extraction, the organic phase consists of 10-15 vol% N235, 5-10 vol% tert-decyl alcohol and 75-85 vol% sulfonated kerosene; the volume ratio of the organic phase to the aqueous phase is controlled at 1:2-1:

4.

8. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, In step S5: the molybdenum-loaded organic phase is back-extracted using 10%-15wt% ammonia water, and the back-extract is crystallized at a low temperature of 1-5℃ to obtain ammonium molybdate; the empty organic phase after back-extraction is washed with 1.0mol / L sulfuric acid solution and then returned to step S4 for recycling.

9. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, The pH gradient control employs a precision meter pump linked with an online pH sensor to control the pH fluctuation range ΔpH≤0.2 at each stage.

10. The multi-metal stepwise leaching and extraction recovery process for molybdenum-lead ore as described in claim 1, characterized in that, The secondary leaching mother liquor generated in the entire process is subjected to alkali recovery via nanofiltration membrane module, and the primary leaching mother liquor is subjected to freeze crystallization to recover sodium chloride.

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