Novel environment-friendly gold extraction agent and preparation method thereof

Abstract

The invention relates to the technical field of mineral processing and environment-friendly chemical agents, in particular to a novel environment-friendly gold extraction agent and a preparation method thereof. The method aims at solving the problems that in existing gold hydrometallurgy, a traditional cyanide gold extraction agent is highly toxic and pollutes the environment, and the environment-friendly gold extraction agent is insufficient in the aspects of leaching efficiency, preparation and application convenience, energy consumption and universality. The method is characterized by comprising the following steps: mixing a bio-based organic complexing agent aqueous solution with the weight-average molecular weight of 500-2000 with an oxidizing agent, adjusting the pH value, adding an inorganic salt auxiliary agent, heating for reaction, and finally carrying out spray drying to obtain the powdery gold extraction agent. By the adoption of the technical scheme, the effects of being environmentally friendly, low in toxicity, high in leaching efficiency, high in universality to complex ore, low in preparation energy consumption, rapid in product dissolution, convenient and fast to apply and the like can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing and environmentally friendly chemical reagents technology, specifically a novel environmentally friendly gold extraction agent and its preparation method. Background Technology

[0002] As a vital strategic resource and precious metal, gold extraction technologies, particularly efficient, economical, and environmentally friendly ones, have long been a focus of research in the field of hydrometallurgy. For a long time, cyanide gold extraction processes have dominated due to their superior leaching efficiency and mature industrial application systems. However, the inherent high toxicity of cyanide poses a serious threat to the ecological environment and human health. The resulting environmental pollution incidents and increasingly stringent environmental regulations have made the industry's need for developing low-toxicity and non-toxic alternative gold extraction agents particularly urgent, driving the widespread exploration and development of non-cyanide gold extraction technologies globally. Against this backdrop, developing novel gold extraction agents that combine high leaching rates, low toxicity, ease of operation, and cost-effectiveness has become a core technological challenge in the current gold hydrometallurgical field.

[0003] To address the aforementioned challenges, existing technologies have proposed various environmentally friendly gold extraction agent solutions. For example, Chinese Patent Publication No. CN109957664B discloses an environmentally friendly gold extraction agent and its preparation method. This gold extraction agent mainly consists of sodium humate, soda ash, urea, and a gold leaching activator. Its core technical idea lies in utilizing sodium humate to form complex ions with gold under high-temperature conditions, thereby achieving the dissolution of gold. The advantage of this solution is that its components have low toxicity, and the raw material cost is relatively controllable, providing an alternative to cyanide gold extraction processes to some extent. Correspondingly, another Chinese Patent Publication No. CN112981130B proposes an environmentally friendly gold extraction agent and its preparation method. The gold extraction agent formula disclosed in this patent is more complex, containing a variety of conventional low-toxicity or non-toxic chemical raw materials such as sodium cyanate, sodium hydroxide, sodium chloride, potassium chloride, barium chloride, ferric chloride, aminosulfonic acid, disodium hydrogen phosphate, and trisodium citrate. This technical approach aims to ensure the avoidance of the generation of highly toxic substances during production and application through the synergistic effect of multiple components, and to expand its applicability to a variety of complex gold mines, including low-arsenic and low-sulfur ores, reflecting its efforts in environmental protection and ore adaptability.

[0004] However, with the continuous development of related technologies and the increasingly stringent requirements for performance indicators in application scenarios, some inherent characteristics of the above-mentioned technical solutions at the principle level have gradually revealed their limitations in dealing with new challenges.

[0005] Specifically, regarding the gold extraction agent based on sodium humate disclosed in CN109957664B, although it has the advantages of low cost and low toxicity, its leaching efficiency is relatively insufficient, especially when processing complex ores, its adaptability often fails to meet the needs of industrial production. The underlying reason is that sodium humate, as a natural macromolecular organic compound, has a complex and highly heterogeneous structure. This limits its efficiency in forming stable complexes with gold ions, as it is constrained by the number and spatial accessibility of specific active sites in its molecular structure, and the reaction kinetics may be slow. Furthermore, this preparation process relies on high-temperature complexation reactions, which not only significantly increases energy consumption, contradicting the requirements of modern industry for green and low-carbon production, but also results in solid block or granular products requiring long dissolution times in practical applications. This directly affects production efficiency and operational convenience, revealing an inherent contradiction between conversion efficiency and ease of application.

[0006] Meanwhile, the gold extraction agent disclosed in CN112981130B, while striving to improve overall performance by integrating multiple low-toxic or non-toxic components, presents new challenges due to the complexity of its formulation. Involving the precise proportioning of up to nine or more chemical raw materials significantly increases the difficulty of quality control in industrial production, not only substantially increasing production costs but also significantly increasing the complexity and instability of the process in actual operation. More importantly, even with such a complex formulation design, the leaching efficiency and selectivity of this gold extraction agent still have room for further optimization when treating some difficult-to-process ores. While the introduction of this complex system theoretically provides multiple mechanisms of action, in practice it may lead to potential side reactions between components, mutual inhibition of activity, or poor synergistic effects under non-ideal operating conditions, thus failing to fundamentally solve the problem of efficient and stable leaching of complex ores. Neither of these two existing technological approaches—whether seeking low cost and high environmental friendliness through a single macromolecular component system or pursuing broad-spectrum adaptability through a multi-component complex system—has been able to effectively balance multiple key indicators such as gold extraction efficiency, ease of preparation and application, and cost-effectiveness. Their inherent defects are becoming increasingly prominent under the increasingly stringent requirements of industrial production.

[0007] The above analysis shows that existing environmentally friendly gold extraction agents, while reducing toxicity, still generally suffer from a series of interconnected technical bottlenecks, including low leaching efficiency, complex preparation processes or high energy consumption, slow product dissolution rates, and insufficient applicability to various complex ores. Therefore, how to simplify the preparation process of gold extraction agents, reduce energy consumption, and significantly improve their leaching efficiency, dissolution rate, and applicability to various complex ores while taking into account environmental characteristics, and construct a gold extraction technology that is both efficient, economical, and environmentally friendly, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0008] This invention provides a novel environmentally friendly gold extraction agent and its preparation method, aiming to solve the inherent high toxicity and environmental pollution problems of traditional gold extraction agents, represented by cyanide, in the field of existing gold hydrometallurgy, as well as the limitations and technical bottlenecks of existing environmentally friendly gold extraction agents in terms of leaching efficiency, ease of preparation and application, energy consumption control, and universality to complex ores.

[0009] To achieve the above-mentioned objectives, this invention provides a novel environmentally friendly gold extraction agent preparation method. This method, through the synergistic application of multiple reaction mechanisms and refined process control, yields a gold extraction agent product with high leaching efficiency, rapid solubility, low toxicity, and good ore adaptability. Specifically, the preparation method includes the following steps:

[0010] Step S10: Dissolve the organic complexing agent in water to obtain an aqueous solution of the organic complexing agent. The organic complexing agent is a bio-based compound whose molecular structure contains abundant carboxyl and hydroxyl functional groups, and whose weight-average molecular weight (Mw) is strictly controlled within the range of 500 to 2000. In a preferred embodiment of the present invention, the bio-based compound may be an oligosaccharide acid or its derivative obtained by controlled degradation methods such as enzymatic hydrolysis, acid hydrolysis, or alkaline hydrolysis from natural biomass (e.g., plant cellulose, hemicellulose, pectin, or lignin), for example, carboxymethyl oligodextrin, oxidized maltodextrin, or modified lignin sulfonates within a specific molecular weight range. The purity of the organic complexing agent is not less than 95% to ensure the specificity of subsequent reactions and the activity of the product. To achieve complete dissolution of the organic complexing agent, the dissolution process can be carried out at a temperature range of 20°C to 40°C, supplemented by continuous stirring at a stirring rate of 100 rpm to 300 rpm for 30 to 90 minutes, until a clear, transparent, or slightly turbid homogeneous solution is formed. The conductivity of the water should be below 50 μS / cm to avoid introducing impurity ions that may affect subsequent reactions. The initial concentration of the organic complexing agent in water is preferably 10% to 25% (w / v). The carboxyl group content in the organic complexing agent can be determined by titration, preferably between 1.0 mmol / g and 3.0 mmol / g; the hydroxyl group content can be determined by nuclear magnetic resonance spectroscopy or chemical derivatization, preferably between 3.0 mmol / g and 6.0 mmol / g. The synergistic effect of the carboxyl and hydroxyl groups constitutes the key active site for complexing gold ions. The selection of the molecular weight range is based on a comprehensive consideration of its gold ion complexing efficiency, dissolution rate and stability in aqueous systems, and adaptability to subsequent spray drying. A molecular weight that is too low may result in insufficient complexing ability or easy degradation in the reaction system, while a molecular weight that is too high may increase the viscosity of the solution, reduce the dissolution rate, and have an adverse effect on the atomization efficiency and drying uniformity in the spray drying process.

[0011] Step S20: Add an oxidant to the aqueous solution of the organic complexing agent, stir until homogeneous, and adjust the pH to 8 or 9 to form a mixed solution. The oxidant is either hydrogen peroxide or potassium permanganate. The amount of the oxidant is strictly controlled to be 10% to 30% of the mass of the organic complexing agent. Preferably, the oxidant is a 30% (w / w) aqueous solution of hydrogen peroxide, and its amount is 15% to 25% of the mass of the organic complexing agent. The addition of the oxidant aims to moderately oxidize and modify the organic complexing agent molecules, thereby exposing more active complexing sites and improving its stability under redox conditions. Specifically, hydrogen peroxide or potassium permanganate can oxidize some of the alcohol hydroxyl groups in the organic complexing agent to generate additional carboxyl or aldehyde groups, further enhancing its complexing ability for gold ions, or removing reducing impurities that may be present in the solution. The addition rate of the oxidant should be slow and uniform to avoid excessive degradation or aggregation of the organic complexing agent due to localized overoxidation reactions. The stirring rate should be maintained between 200 and 400 rpm to ensure thorough mixing and reaction between the oxidant and the organic complexing agent. The pH value is adjusted to 8 to 9 by adding an alkaline solution, preferably a 20% to 30% aqueous solution of sodium hydroxide or potassium hydroxide. This pH range ensures that the carboxyl groups in the organic complexing agent are effectively deprotonated, existing as carboxylate ions, thereby enhancing its electrostatic attraction and complexing ability for gold ions. It also avoids the problems of hydrolysis of the organic complexing agent under strongly acidic conditions or excessively rapid decomposition of the oxidant under strongly alkaline conditions. Precise pH control can be achieved through real-time monitoring and automatic replenishment using an online pH meter, with an error range controlled within ±0.1 pH units.

[0012] Step S30: Add an inorganic salt auxiliary to the mixed solution, continue stirring and heating to 40°C to 60°C, and react for 1 to 3 hours. The inorganic salt auxiliary is either sodium sulfate or potassium chloride. The amount of the inorganic salt auxiliary is 50% to 100% of the mass of the organic complexing agent. Preferably, the inorganic salt auxiliary is analytical grade anhydrous sodium sulfate, and its amount is 70% to 90% of the mass of the organic complexing agent. The inorganic salt auxiliary plays multiple key roles in this step. First, as an ionic strength regulator, it can effectively maintain the ionic balance of the solution, reduce the electrostatic repulsion or attraction between organic complexing agent molecules, thereby preventing undesirable aggregation or precipitation during subsequent heating, and ensuring the homogeneity of the solution and the stability of the reaction. Second, the anions (e.g., sulfate or chloride ions) in the inorganic salt auxiliary can, to a certain extent, act as auxiliary complexing ligands for gold ion leaching, or as intermediate media for charge transfer, promoting the conversion of gold atoms to gold ions under oxidizing conditions and stabilizing the gold complex. Third, the inorganic salt additive can effectively reduce the surface tension of the solution, which is beneficial to the formation and uniform dispersion of atomized droplets during subsequent spray drying. The heating process can be carried out in a reaction vessel with temperature control and stirring functions, and precise temperature control can be achieved through jacket heating or electric heating, with a temperature fluctuation range not exceeding ±1℃. The stirring rate should be adjusted to 300 rpm to 500 rpm to ensure uniform temperature distribution and sufficient contact of reactants. The reaction time of 1 to 3 hours is based on a comprehensive consideration of the degree of oxidation modification of the organic complexing agent, the efficiency of gold complexing active site formation, and energy consumption. Too short a time may lead to incomplete reaction and insufficient formation of active sites; too long a time may cause excessive oxidation or degradation of the organic complexing agent, while increasing energy consumption. After the reaction is completed, the mixture is a uniform light yellow to brownish-yellow liquid with no obvious precipitation or stratification.

[0013] Step S40: Cool the reacted mixture to room temperature and spray dry to obtain a novel, environmentally friendly gold extractant in powder form. The cooling process can be carried out using circulating cooling water or natural cooling, with the cooling rate controlled at 1°C to 5°C per minute to avoid component separation or gelation due to rapid cooling. Spray drying can be performed when the mixture temperature drops to 25°C ± 5°C. The spray drying process uses typical laboratory or industrial-scale spray drying equipment. This equipment includes an atomizer, a drying chamber, a heater, and a cyclone separator. The atomizer preferably uses a dual-fluid nozzle or a centrifugal atomizing disc to produce uniform, fine droplets. The inlet air temperature for spray drying should be controlled between 150°C and 200°C, and the outlet air temperature should be controlled between 70°C and 90°C. The inlet air rate should be adjusted according to the solid content and viscosity of the solution, typically between 50 cubic meters per hour and 150 cubic meters per hour. The atomization pressure should be controlled between 0.2 MPa and 0.6 MPa. Powder collection can be carried out using a cyclone separator and / or a bag filter. The powdered gold extractant obtained by spray drying has the following significant advantages: First, it has a uniform particle size distribution, preferably with an average particle size of 10 to 50 micrometers, and a large specific surface area. This results in extremely high dissolution rate and dispersibility when applied to aqueous solutions, allowing it to completely dissolve in a short time to form a uniform gold immersion solution, significantly shortening on-site preparation time and improving operational convenience. Second, the powdered product is easy to store and transport, and has high stability, not easily deliquescing or clumping. Third, the spray drying process effectively removes moisture from the mixture, obtaining a solid product with high solid content, high purity, and stable activity, avoiding the defects of slow dissolution and easy clumping of traditional block or granular products. The free flowability of the obtained powder is preferably higher than 80%, and the moisture content is lower than 3%.

[0014] The novel environmentally friendly gold extraction agent prepared in this invention is based on a core technology principle that constructs a composite system consisting of an optimized and modified bio-based organic complexing agent, a specific amount of oxidant, and an inorganic salt auxiliary agent working synergistically. As mentioned earlier, the bio-based organic complexing agent has a controllable molecular weight and a high density of carboxyl and hydroxyl groups. These functional groups can form stable, soluble polynuclear or mononuclear complexes with gold ions (Au(I) or Au(III)) through multi-site coordination under weakly alkaline conditions, thereby achieving effective gold leaching. The bio-based characteristics and specific molecular structure of the complexing agent give it good dispersibility and resistance to biodegradation in solution, while ensuring its environmental friendliness and extremely low toxicity. The oxidant (such as hydrogen peroxide) not only participates in the activation of the organic complexing agent during preparation, but also provides the necessary oxidation potential for the oxidative dissolution of gold in subsequent gold leaching applications. Especially for complex ores containing reducing mineral components such as sulfides and arsenides, the oxidant can effectively passivate the surface of these interfering substances, preventing them from competing with gold for the oxidant or preventing them from forming a passivation film on the gold surface, thereby maintaining the continuous oxidative dissolution of gold. The inorganic salt additive further optimizes the overall performance of the leaching system by adjusting the ionic strength of the solution, stabilizing the spatial structure of the complexing agent, and promoting effective contact between gold ions and the complexing agent. This three-component synergistic system exhibits superior leaching efficiency and selectivity compared to existing technologies with single components or complex components and unclear mechanisms of action.

[0015] Furthermore, the gold extraction agent prepared by this invention is soluble in water to form a gold leaching solution, which can be used to leach gold-bearing ores under normal temperature (15°C to 40°C) and weakly alkaline conditions (pH 8.5 to 11.0). The effective gold extraction agent concentration of the leaching solution can be adjusted according to the ore grade and type, typically from 0.5 g / L to 5.0 g / L. During the leaching process, aeration or the addition of other oxidants (e.g., sodium hypochlorite, air, or pure oxygen) can be used to provide sufficient dissolved oxygen and promote the oxidative dissolution of gold. The solid-liquid ratio of the gold leaching pulp can be from 1:2 to 1:5. The leaching time is typically from 12 hours to 48 hours, depending on the properties of the ore. The stable complexes formed after gold dissolution can be recovered from the leaching solution using conventional methods such as activated carbon adsorption, zinc powder replacement, or ion exchange resin adsorption. The gold extraction agent prepared by this invention exhibits excellent leaching effects on a variety of complex gold ores, including oxide ores, sulfide ores, carbonaceous ores, and copper-gold symbiotic ores, effectively solving the shortcomings of existing technologies in terms of ore universality.

[0016] As a more specific embodiment of the present invention, the preparation of the organic complexing agent in step S10 may include the following sub-steps: pre-treating agricultural and forestry waste (e.g., straw, rice husks, sawdust, etc.) and then subjecting it to mild hydrolysis or enzymatic hydrolysis to obtain a mixture of low molecular weight polysaccharides or their derivatives; subjecting the mixture to a selective oxidation reaction to introduce carboxyl functional groups while controlling the molecular weight distribution; and finally purifying it using membrane separation techniques such as ultrafiltration or dialysis to obtain a product with a weight-average molecular weight of 500 to 2000 and a carboxyl and hydroxyl content that meets the requirements. This refined preparation process ensures the uniformity of the organic complexing agent structure and the controllability of the active sites, which is significantly better than the complex heterogeneity of natural sodium humate.

[0017] In a further preferred embodiment of the present invention, the addition of the oxidant in step S20 can be performed under precisely controlled redox potential (ORP). The dropping rate of the oxidant is dynamically adjusted by real-time monitoring of the solution's ORP value and according to a set target ORP range (e.g., after the addition of the oxidant, the ORP value should rise rapidly and stabilize at 200 mV to 400 mV vs. Ag / AgCl reference electrode). This further optimizes the activation degree of the organic complexing agent, avoids under-oxidation or over-oxidation, and ensures the stability and activity of the final product.

[0018] In another preferred embodiment of the present invention, after the heating reaction in step S30 is completed, an additional filtration process can be performed to remove any trace amounts of insoluble substances or reaction byproducts, thereby improving the purity of the final gold extraction agent product. The filtration can be performed using a microporous membrane with a diameter of 0.2 to 0.5 micrometers for precision filtration. This operation plays a positive role in ensuring the stable operation of the spray drying equipment and the purity of the final powder.

[0019] The novel environmentally friendly gold extraction agent and its preparation method disclosed in this invention have the following significant technical effects and advantages compared with existing technologies: First, the organic complexing agent used in this invention has undergone structural optimization and molecular weight control, resulting in a high density of active sites that easily complex with gold ions. Combined with the synergistic activation effect of the oxidant, it significantly improves the gold leaching efficiency, especially exhibiting stronger adaptability and leaching ability for difficult-to-process complex gold ores, effectively overcoming the inherent defect of low leaching efficiency in traditional humic acid gold extraction agents. Second, this invention significantly reduces the energy consumption of the preparation process by carrying out key oxidation modification and synergistic reactions at a relatively low temperature (40℃ to 60℃), which meets the requirements of modern industry for green and low-carbon production compared to some existing technologies that require high-temperature complexation. Third, the gold extraction agent prepared by this invention is a uniform powder product with excellent water solubility and dispersibility, which can dissolve rapidly in a short time to form a stable gold leaching solution. This greatly improves the ease of on-site preparation and application, avoiding the disadvantages of slow dissolution and the need for long soaking and stirring required by traditional block or granular gold extraction agents, thereby improving production efficiency. Fourth, the gold extraction agent formulation of this invention consists of three carefully selected core components, each with a clear mechanism of action and significant synergistic effects. This avoids the problems of difficult production quality control, high costs, and potential negative interference between components associated with some existing multi-component complex formulations. The process flow of this method is simplified, facilitating industrial-scale production and quality control. Fifth, the raw materials used in this invention are all bio-based or low-toxic / non-toxic commonly used chemical raw materials, eliminating the introduction and use of highly toxic substances at the source. This is environmentally friendly, significantly reducing environmental risks and health risks to operators, and meeting increasingly stringent environmental regulations. Sixth, the gold extraction agent of this invention exhibits high selectivity for gold during the leaching process, effectively inhibiting the co-leaching of base metals such as copper and iron, reducing impurity interference in subsequent gold recovery stages, and improving gold recovery rate and product purity. In summary, this invention simplifies the gold extraction agent preparation process and reduces energy consumption while taking into account environmental protection characteristics. At the same time, it significantly improves the leaching efficiency, dissolution rate, and applicability to various complex ores, thus constructing a gold extraction technology solution that is both efficient and economical and environmentally friendly. It effectively solves the multiple contradictions between efficiency, cost, environment, and ease of operation in existing technologies, and has significant industrial application value and broad market prospects. Detailed Implementation

[0020] This invention focuses on disclosing a novel environmentally friendly gold extraction agent and its preparation method, aiming to overcome the challenges faced by existing gold hydrometallurgical technologies in terms of efficiency, environmental friendliness, economy, and versatility through systematic engineering design and refined process control. The core of the gold extraction agent prepared by this invention lies in constructing a composite system consisting of an optimized and modified bio-based organic complexing agent, a specific amount of oxidant, and an inorganic salt auxiliary agent working synergistically. This system achieves a delicate balance at both the molecular and macroscopic process levels, thereby significantly improving the leaching efficiency, dissolution rate, and adaptability to various complex gold ores while maintaining low toxicity and environmental friendliness. The following detailed description of the invention, including specific implementation steps, parameter settings, and mechanisms of action, will ensure that those skilled in the art can fully understand and implement this invention.

[0021] In one specific embodiment, the present invention provides a method for preparing a novel environmentally friendly gold extraction agent. This method strictly follows the following core steps to ensure the superior performance of the final product:

[0022] Step S10: Precise dissolution and pretreatment of organic complexing agents

[0023] This step aims to efficiently and uniformly dissolve the selected bio-based organic complexing agent in high-purity water, laying a stable homogeneous foundation for subsequent oxidation modification and synergistic reactions. The organic complexing agent, as the core coordinating component of the gold extraction system of this invention, has a carefully designed and screened molecular structure rich in carboxyl and hydroxyl functional groups. These groups constitute the key active sites for multi-site coordination complexation with gold ions. To ensure that the complexing agent can fully exert its function, its weight-average molecular weight (Mw) is strictly controlled between 500 and 2000. This molecular weight range is selected based on a comprehensive consideration of gold ion complexation efficiency, dissolution rate and stability in the aqueous system, and adaptability to subsequent spray drying. Organic complexing agents with a weight-average molecular weight below 500 may diffuse too quickly in aqueous systems, resulting in insufficient contact time with gold ions, or have insufficient complexing ability due to overly simple molecular structures, or even be prone to uncontrollable degradation in the reaction system. On the other hand, organic complexing agents with a weight-average molecular weight above 2000 will significantly increase the viscosity of the aqueous solution, thereby reducing its dissolution rate and adversely affecting the atomization efficiency and droplet uniformity in the subsequent spray drying process, which may lead to incomplete drying or uneven powder particle size distribution.

[0024] In a preferred embodiment of the present invention, the bio-based organic complexing agent may be specifically selected from oligosaccharide acids or their derivatives obtained by controlled degradation from natural biomass. For example, agricultural and forestry waste, such as corn stalks, rice husks, sawdust, or bagasse, may be used, which, after pretreatment (such as crushing, washing, and degreasing), undergo mild hydrolysis or enzymatic hydrolysis. Mild hydrolysis is typically carried out at 90°C to 120°C for 1 to 3 hours under dilute acid (such as 0.5% to 2% sulfuric acid) or dilute alkali (such as 0.5% to 1% sodium hydroxide) conditions, aiming to selectively break glycosidic bonds in the biomass to generate a mixture of low molecular weight polysaccharides or their derivatives. Enzymatic hydrolysis can be carried out using specific enzyme preparations such as cellulase, hemicellulase, or pectinase at mild pH (typically 4.5 to 6.0) and temperature (typically 40°C to 60°C) to obtain products within the target molecular weight range.

[0025] Subsequently, the mixture of the low molecular weight polysaccharide or its derivatives is subjected to a selective oxidation reaction to introduce carboxyl functional groups. This oxidation process can be carried out in the presence of a mild oxidant, such as sodium hypochlorite, peracetic acid, or even air / oxygen in the presence of a specific catalyst. For example, the pH of the hydrolysis product solution can be adjusted to 7 to 9, and a 5% to 10% sodium hypochlorite solution can be slowly added dropwise with continuous stirring, the reaction temperature controlled at 40°C to 50°C, and the reaction time at 2 to 6 hours. By controlling the amount of oxidant added and the reaction time, the number of carboxyl groups introduced can be precisely controlled, while minimizing molecular weight degradation. During the oxidation process, the redox potential (ORP) of the solution should be monitored in real time to ensure the mildness and controllability of the oxidation reaction.

[0026] Finally, to obtain the target product with high purity and a narrow molecular weight distribution, membrane separation techniques such as ultrafiltration or dialysis can be used for purification. For example, by using ultrafiltration membranes with different molecular weight cutoffs (NMWL) in series, components with excessively large or small molecular weights, as well as other impurities, can be effectively removed, thereby obtaining a product with a weight-average molecular weight of 500 to 2000 and the required carboxyl and hydroxyl content. The purified organic complexing agent should have a purity of not less than 95% to minimize the interference of impurities on subsequent reactions and the performance of the final gold extraction agent. The carboxyl content can be determined by standard acid-base titration (e.g., titration with 0.1M NaOH), preferably between 1.0 mmol / g and 3.0 mmol / g; the hydroxyl content can be determined by nuclear magnetic resonance spectroscopy (e.g., 1H NMR combined with specific derivatization) or chemical derivatization methods (e.g., esterification titration), preferably between 3.0 mmol / g and 6.0 mmol / g. The synergistic effect of these active functional groups is the structural basis for its effective complexing alloy ions.

[0027] When dissolving the purified organic complexing agent in water, the conductivity of the water should be strictly below 50 μS / cm. Deionized water or ultrapure water is typically used to avoid introducing impurity ions that may adversely react with the complexing agent or gold ions. The dissolution process can be carried out in a glass or stainless steel reactor equipped with a stirrer, with the temperature controlled between 20°C and 40°C. This temperature range helps to accelerate the dissolution rate while avoiding thermal degradation of the organic complexing agent. The stirring rate should be maintained between 100 rpm and 300 rpm to ensure sufficient particle dispersion and accelerate dissolution, avoiding excessively high local concentrations that could lead to clumping. The dissolution time is typically 30 to 90 minutes, until a clear, transparent, or slightly turbid homogeneous solution is formed, with no visible insoluble matter. The initial concentration of the organic complexing agent in water is preferably 10% to 25% (w / v). This concentration range ensures the material concentration requirements for subsequent reactions while avoiding excessively high solution viscosity that could lead to difficulties in stirring or decreased mass transfer efficiency.

[0028] Step S20: Precise introduction of oxidant and strict control of pH conditions

[0029] This step aims to moderately modify the organic complexing agent molecule through precisely controlled oxidation reactions, exposing more active complexing sites and enhancing its stability under redox conditions. Simultaneously, by precisely adjusting the pH value, the ionization state of the active functional groups in the organic complexing agent is optimized, thereby enhancing its complexing ability for gold ions.

[0030] A selected oxidant is slowly and uniformly added to the aqueous solution of the organic complexing agent obtained in step S10. The oxidant may be a 30% (w / w) aqueous solution of hydrogen peroxide or a potassium permanganate solution (e.g., 1% to 5% (w / w)). In a preferred embodiment of the invention, a 30% (w / w) aqueous solution of hydrogen peroxide is used, with the amount strictly controlled to be 15% to 25% of the mass of the organic complexing agent. Hydrogen peroxide, as a mild and environmentally friendly oxidant, can selectively oxidize some of the alcohol hydroxyl groups in the organic complexing agent under specific conditions, generating additional carboxyl or aldehyde groups, thereby significantly increasing its complexing ability for gold ions and improving the density of active sites. Furthermore, hydrogen peroxide can effectively remove trace amounts of reducing impurities that may be present in the solution, ensuring the purity of subsequent reactions. The rate of oxidant addition is crucial; it should be slowly added dropwise at a rate of 10 mL / min to 50 mL / min using a metering pump or burette, while maintaining stirring, to avoid excessive local concentrations that could lead to excessive degradation or aggregation of the organic complexing agent, thereby affecting its molecular structural integrity and activity. The stirring rate should be maintained at 200 to 400 rpm during this stage to ensure that the oxidant and organic complexing agent are fully mixed and react uniformly.

[0031] After the oxidant is added and stirred evenly, the pH of the solution is immediately adjusted. The pH is adjusted to 8 to 9 by adding an alkaline solution. The alkaline solution is preferably a 20% to 30% aqueous solution of sodium hydroxide or potassium hydroxide. This pH range serves multiple purposes: First, in this weakly alkaline environment, the carboxyl groups in the organic complexing agent can be effectively deprotonated, existing as carboxylate ions (-COO-). As a strong coordinating group, the carboxylate ion significantly enhances its binding ability to gold ions through electrostatic attraction and the formation of coordinate bonds. Second, this pH range avoids the problems of hydrolysis of the organic complexing agent under strongly acidic conditions or excessively rapid decomposition of oxidants such as hydrogen peroxide under strongly alkaline conditions, thus ensuring the stability and controllability of the reaction system.

[0032] Precise pH control is crucial and can be achieved through real-time monitoring and automatic replenishment using an online pH meter. The online pH meter should have a measurement accuracy of at least 0.01 pH units and be linked to the alkali metering pump via a PLC (Programmable Logic Controller) to ensure that pH fluctuations are precisely controlled within ±0.1 pH units. This real-time monitoring and feedback control system significantly improves the automation level of the preparation process and the consistency between product batches.

[0033] In a further preferred embodiment of the present invention, the addition of the oxidant in step S20 can be carried out under precisely controlled oxidation-reduction potential (ORP). The ORP value of the solution is monitored in real time by installing an online ORP sensor (e.g., a platinum electrode and an Ag / AgCl reference electrode) inside the reactor. During the oxidant addition process, a target ORP range is set (e.g., after the addition of the oxidant, the ORP value should rise rapidly and stabilize at 200 mV to 400 mV vs. Ag / AgCl reference electrode), and the oxidant addition rate is dynamically adjusted based on the real-time ORP value. If the ORP value is below the target range, the oxidant addition is accelerated; if it is above the target range, the addition is slowed down. This further optimizes the activation degree of the organic complexing agent, avoiding insufficient oxidation leading to inadequate formation of active sites, or excessive oxidation leading to degradation of the organic complexing agent structure and decreased complexing ability, thereby ensuring the high stability and high activity of the final product. Precise control of ORP is a key technical means to ensure the consistency of the activation effect of the organic complexing agent.

[0034] Step S30: Synergistic effect of inorganic salt auxiliaries and optimization of reaction conditions

[0035] This step introduces an inorganic salt auxiliary agent and, through precise heating and stirring, promotes the full reaction of the components in the system, further stabilizing the structure of the organic complexing agent and optimizing its performance in the subsequent leaching process. The inorganic salt auxiliary agent is added to the mixed solution obtained in step S20. The inorganic salt auxiliary agent can be either analytical grade anhydrous sodium sulfate or potassium chloride. The amount of the inorganic salt auxiliary agent should be precisely proportioned according to the mass of the organic complexing agent, ranging from 50% to 100% of the mass of the organic complexing agent. As a preferred embodiment of the present invention, analytical grade anhydrous sodium sulfate is selected, and its amount is preferably 70% to 90% of the mass of the organic complexing agent.

[0036] The inorganic salt additive plays multiple key roles in this step: First, as an ionic strength regulator, it effectively maintains the ionic balance of the solution by introducing a large number of inert ions (such as Na+ and SO4^2- or K+ and Cl-), significantly reducing the electrostatic repulsion or attraction between organic complexing agent molecules. This prevents undesirable aggregation, precipitation, or gelation due to excessively strong intermolecular forces during subsequent heating, ensuring the homogeneity of the solution and the stability of the reaction. This ion shielding effect is crucial for maintaining the stable dispersion of macromolecular compounds in complex systems. Second, the anions (such as sulfate or chloride ions) in the inorganic salt additive can, to some extent, act as auxiliary complexing ligands for gold ion leaching. These anions may form weak intermediate complexes with gold ions or act as intermediate mediators for charge transfer, promoting the conversion of gold atoms to gold ions under oxidative conditions and stabilizing the gold complex, thereby accelerating the dissolution rate of gold. Third, the inorganic salt additive can also effectively reduce the surface tension of the solution. Lower surface tension facilitates the formation of atomized droplets during subsequent spray drying, resulting in more uniform and finer droplets, thereby improving drying efficiency and the quality of the obtained powder. This mechanism directly impacts the acquisition of a final product with uniform particle size distribution and a large specific surface area.

[0037] After the inorganic salt additive is added, the mixture is continuously stirred and heated. The heating process can be carried out in a glass-lined reactor or a stainless steel reactor equipped with temperature control and stirring functions. Heating can be achieved using jacketed heating or electric heating, coupled with a high-precision PID (proportional-integral-derivative) temperature controller to achieve precise temperature control, ensuring that the reaction temperature fluctuation range does not exceed ±1℃. The reaction temperature should be controlled between 40℃ and 60℃. This temperature range provides sufficient activation energy to promote the oxidative modification of the organic complexing agent and the formation of gold complexing active sites, while effectively avoiding excessive degradation of the organic complexing agent or rapid decomposition of the oxidant due to excessively high temperatures. The stirring rate should be adjusted to 300 rpm to 500 rpm during this stage to ensure uniform temperature distribution in the system, promote sufficient contact and efficient reaction of the reactants, and prevent localized overheating or concentration gradients.

[0038] The reaction time is set to 1 to 3 hours. This time range is based on a comprehensive consideration of the degree of oxidation modification of the organic complexing agent, the efficiency of gold complexing active site formation, and energy consumption. Too short a reaction time may lead to insufficient activation of the organic complexing agent and insufficient formation of active sites, thus affecting the gold extraction efficiency of the final product; while too long a reaction time may cause excessive oxidation or degradation of the organic complexing agent, resulting in a decrease in complexing ability and a significant increase in energy consumption, which does not conform to the principles of green and low-carbon production. By precisely controlling the reaction time, production costs can be optimized to the maximum extent while ensuring product performance. After the reaction is completed, the mixture should be a uniform light yellow to brownish-yellow liquid without obvious precipitation or stratification, indicating that the components have fully reacted and formed a stable homogeneous system.

[0039] In another preferred embodiment of the present invention, after the heating reaction in step S30 is completed, an additional filtration process can be performed to remove any trace amounts of insoluble substances or reaction byproducts, thereby further improving the purity of the final gold extraction agent product. The filtration can be performed using a pressure filtration device equipped with a microporous membrane of 0.2 to 0.5 micrometers for precision filtration. This operation plays a positive role in ensuring the stable operation of the subsequent spray drying equipment (avoiding nozzle clogging) and the purity, dispersibility, and storage stability of the final powder product. The filtered clear liquid will be sent to the next step for spray drying.

[0040] Step S40: Precise cooling and efficient spray drying of the mixture

[0041] This step involves cooling the reaction mixture to room temperature and then using spray drying technology to transform it into a highly active, easily soluble, powdered, environmentally friendly gold extraction agent, thereby greatly improving the product's ease of application and storage stability.

[0042] First, the reacted mixture is transferred from the reactor to a cooling tank or cooled directly within the reactor. Cooling can be achieved through circulating cooling water or natural cooling. To avoid component leaching, insoluble formation, or gelation due to rapid cooling, the cooling rate should be strictly controlled between 1°C and 5°C per minute. For example, the heating medium in the jacket can be replaced with circulating cooling water, and the water flow rate can be adjusted to control the cooling rate. Cooling is considered complete when the mixture temperature drops to 25°C ± 5°C (i.e., room temperature). At this point, the solution viscosity is suitable for spray drying.

[0043] The cooled mixture is then fed into a spray drying apparatus for drying. The spray drying process utilizes typical laboratory or industrial-scale spray drying equipment. This equipment typically includes the following key components: a precise feed pump (such as a peristaltic pump or diaphragm pump) for delivering the mixture to an atomizer at a constant flow rate; an atomizer responsible for dispersing the liquid into extremely fine droplets; a drying chamber to provide the drying environment; a heater for heating the drying air; and a cyclone separator and / or bag filter for collecting the dried powder product.

[0044] The atomizer preferably employs a dual-fluid nozzle or a centrifugal atomizing disc. A dual-fluid nozzle mixes the liquid feed with a high-speed airflow (typically compressed air or nitrogen), atomizing the liquid into fine droplets. The atomization pressure should be controlled between 0.2 MPa and 0.6 MPa, which is crucial for the uniformity and fineness of the droplet size. A centrifugal atomizing disc, on the other hand, atomizes the liquid feed by high-speed rotation (typically 10,000 RPM to 25,000 RPM). Selecting an appropriate atomizer type and parameters aims to obtain uniform, fine droplets with an average particle size of 10 to 50 micrometers.

[0045] The inlet air temperature for spray drying should be controlled between 150℃ and 200℃, and the outlet air temperature between 70℃ and 90℃. The inlet air temperature directly affects the drying rate; a higher inlet air temperature can quickly evaporate moisture, but excessively high temperatures may lead to the degradation of the organic complexing agent. The outlet air temperature reflects the moisture content of the product; maintaining it between 70℃ and 90℃ ensures that the product is fully dried without affecting its activity. The inlet air rate should be dynamically adjusted according to the solid content and viscosity of the solution, typically between 50 cubic meters per hour and 150 cubic meters per hour, to ensure sufficient heat and mass transfer efficiency, while avoiding excessive residence time of the powder in the drying chamber, which could lead to thermal degradation or adhesion to the walls.

[0046] The powdered gold extractant obtained from spray drying is efficiently collected using a cyclone separator and / or a bag filter. The cyclone separator is mainly used to collect coarser particles, while the bag filter is used to capture fine dust, ensuring product recovery rate. The resulting powdered gold extractant has the following significant advantages: First, it has a uniform particle size distribution, preferably with an average particle size of 10 to 50 micrometers, and a large specific surface area (typically 5 to 20 m² / g), which gives it extremely high dissolution rate and dispersibility when applied to aqueous solutions. Under stirring conditions, the powder can completely dissolve in a short time (typically within 5 to 15 minutes) to form a homogeneous gold immersion solution, significantly shortening on-site preparation time, improving operational convenience, and avoiding the disadvantages of slow dissolution and the need for long soaking and stirring required by traditional block or granular gold extractants. Second, the powdered product is easy to store and transport, and has high stability. Because of its extremely low moisture content (usually below 3%) and non-crystalline or microcrystalline structure, it is not prone to deliquescence or clumping, and maintains good free flowability even in humid environments (preferably above 80%), thus extending the product's shelf life. Third, the spray drying process effectively removes most of the moisture from the mixture, resulting in a solid product with high solid content, high purity, and stable activity, avoiding the drawbacks of traditional liquid gold extraction agents such as high transportation costs, large storage volume, and susceptibility to microbial contamination.

[0047] The novel environmentally friendly gold extraction agent prepared in this invention is based on a core technology principle that constructs a composite system consisting of an optimized and modified bio-based organic complexing agent, a specific amount of oxidant, and an inorganic salt auxiliary agent working synergistically. As mentioned earlier, the bio-based organic complexing agent has a controllable molecular weight and a high density of carboxyl and hydroxyl groups. These functional groups can form stable, soluble polynuclear or mononuclear complexes with gold ions (Au(I) or Au(III)) through multi-site coordination under weakly alkaline conditions, thereby achieving effective gold leaching. The bio-based characteristics and specific molecular structure of the complexing agent give it good dispersibility and resistance to biodegradation in solution, while ensuring its environmental friendliness and extremely low toxicity. Its acute oral toxicity (LD50) is typically greater than 2000 mg / kg, far lower than that of traditional gold extraction agents such as cyanide.

[0048] The oxidant (such as hydrogen peroxide) participates in the activation and modification of the organic complexing agent during the preparation process, increasing the density of active sites in the complexing agent. More importantly, in subsequent gold leaching applications, this oxidant (or additionally added oxidants, such as air or sodium hypochlorite) can provide the necessary oxidation potential for the oxidative dissolution of gold. Gold leaching is a redox process; gold atoms are first oxidized to gold ions, which then form stable complexes with the complexing agent. Sufficient dissolved oxygen or oxidant can continuously drive the oxidative dissolution of gold. Especially for complex ores containing reducing mineral components such as sulfides (e.g., pyrite, arsenopyrite), arsenides, or carbonaceous components, the oxidant can effectively passivate the surface of these interfering substances, preventing them from competing with gold for oxidants or preventing them from forming a dense passivation film on the gold surface, thereby maintaining the continuous oxidative dissolution of gold. The redox potential is typically maintained in the range of 150 mV to 350 mV (vs. Ag / AgCl) during the leaching process to ensure effective oxidation of gold.

[0049] The inorganic salt additive further optimizes the overall performance of the leaching system by adjusting the ionic strength of the solution, stabilizing the spatial structure of the complexing agent, and promoting effective contact between gold ions and the complexing agent. Adjusting the ionic strength maintains the stable presence of various ions and organic macromolecules in the system, preventing unwanted ion precipitation or complexing agent aggregation. Simultaneously, anions (such as sulfate) in the inorganic salt additive can act as bridging ligands in certain situations, assisting the organic complexing agent in forming more stable polynuclear complexes with gold ions. This three-component synergistic system, through the subtle interactions between its components, exhibits superior leaching efficiency and selectivity compared to existing technologies with single components or complex components but unclear mechanisms of action, especially when processing complex ores, where its synergistic advantages are even more significant.

[0050] The gold extraction agent prepared by this invention can be directly dissolved in water to form a gold leaching solution. This solution can be used to leach gold-bearing ores under normal temperature (preferably 15°C to 40°C) and weakly alkaline conditions (pH 8.5 to 11.0). The effective concentration of the gold extraction agent in the leaching solution can be finely adjusted according to the ore grade, mineral composition, and processing volume, and is typically from 0.5 g / L to 5.0 g / L. During the leaching process, to provide sufficient dissolved oxygen to promote the oxidative dissolution of gold, aeration can be supplemented by forced aeration (air flow rate typically 0.5 L / min / L slurry to 2.0 L / min / L slurry), or by adding sodium hypochlorite solution (e.g., active chlorine concentration controlled at 50 ppm to 200 ppm) as an auxiliary oxidant. The solid-liquid ratio of the gold leaching slurry can be adjusted according to the ore properties and process requirements, typically 1:2 to 1:5 (mass ratio). The leaching time is typically 12 to 48 hours, depending on the ore particle size, mineral composition, and the occurrence state of the gold. After leaching, the dissolved gold forms a stable complex, which can be adsorbed by conventional activated carbon adsorption (carbon adsorption capacity typically up to 3000 g gold / ton of carbon), zinc powder replacement (replacement rate up to 99%), or ion exchange resin adsorption (adsorption capacity up to 50 g / ton of carbon). Established methods such as (kg gold / m³ resin) can efficiently recover gold from leachates. The gold extraction agent prepared in this invention exhibits excellent leaching effects on a variety of complex gold ores, including oxide ores, sulfide ores, carbonaceous ores, and copper-gold symbiotic ores. It effectively solves the shortcomings of existing technologies in terms of ore universality and achieves a balance between high selectivity and high recovery rate.

[0051] Example 1: Preparation of a novel environmentally friendly gold extraction agent and its application in oxide gold ore

[0052] This embodiment aims to illustrate in detail the specific preparation process of the novel environmentally friendly gold extraction agent of the present invention, and to verify its leaching efficiency when treating typical oxidized gold ores.

[0053] Preparation of the gold extraction agent: Step S10: Carboxymethyl oligodextrose, purified by enzymatic hydrolysis and ultrafiltration, was selected as the organic complexing agent. Its weight-average molecular weight was determined to be 1200 by gel permeation chromatography (GPC), with a purity of up to 98%. The carboxyl content was determined to be 2.2 mmol / g by titration, and the hydroxyl content was determined to be 4.5 mmol / g by nuclear magnetic resonance (NMR) analysis. 200 g of the carboxymethyl oligodextrose was weighed and slowly added to 1000 mL of deionized water with a conductivity of less than 10 μS / cm. Dissolution was carried out in a 1500 mL glass beaker equipped with a magnetic stirrer, with the temperature controlled at 30°C and the stirring speed set to 200 rpm. Stirring was continued for 60 minutes until a clear, transparent, homogeneous solution was formed.

[0054] Step S20: Add 40 mL of a 30% hydrogen peroxide aqueous solution (equivalent to 20% of the organic complexing agent by mass) slowly dropwise to the above solution at a rate of 20 mL / min using a peristaltic pump. Maintain a stirring rate of 300 rpm during the addition. After the addition is complete, continue stirring for 10 minutes to ensure homogeneity. Subsequently, slowly adjust the pH value using a 25% sodium hydroxide aqueous solution, while monitoring in real-time with an online pH meter, precisely controlling the pH value at 8.5 ± 0.05. During pH adjustment, real-time monitoring with an ORP electrode showed that the solution ORP value rapidly increased and stabilized at 320 mV (vs. Ag / AgCl).

[0055] Step S30: Add 160 g of analytical grade anhydrous sodium sulfate (equivalent to 80% of the organic complexing agent's mass) to the above mixed solution. Adjust the stirring speed to 400 rpm. Place the beaker in a heating mantle equipped with a precise temperature control system and heat to 50°C, maintaining the reaction at this temperature for 2 hours. During this period, temperature fluctuations should be controlled within ±0.5°C. After the reaction is complete, the solution should be a uniform light brownish-yellow color with no obvious precipitate. Subsequently, the reaction solution should be precisely filtered through a 0.45-micron nylon filter membrane to remove any trace amounts of insoluble substances.

[0056] Step S40: The filtered liquid was allowed to cool naturally to 25°C at room temperature (25°C). After cooling, it was dried using a laboratory-grade spray dryer. The specific parameters of the spray dryer were set as follows: feed pump flow rate of 25 ml / min; atomization pressure of 0.4 MPa using a dual-fluid nozzle; inlet air temperature of 180°C; outlet air temperature of 80°C; and inlet air velocity of 100 m³ / h. The powder obtained during the drying process was collected by a cyclone separator. Approximately 340 grams of off-white powdered gold extractant were finally obtained. The average particle size of the powder was measured to be 25 micrometers using a laser particle size analyzer, the moisture content was 1.8% determined by the Karl Fischer method, and the free flowability test result was 85%. The powder has excellent solubility in water and can completely dissolve within 5 minutes.

[0057] Application in Oxide Gold Ore: Gold monoxide ore from a region in Yunnan Province was selected. Its main mineral composition was quartz, sericite, a small amount of pyrite and carbonates, with a gold grade of 5.5 g / t. The ore was crushed and ground to -74 micrometers (200 mesh), with 85% of the particles being 200 mesh. Leaching experiments were conducted in a 2-liter stirred tank. 500 g of the ground ore was weighed and added to 1500 mL of deionized water to form a slurry with a solid-liquid ratio of 1:3 (w / v). The stirrer speed was set to 400 rpm. The novel environmentally friendly gold extraction agent prepared above was added to the slurry at a concentration of 2.0 g / L. Dissolved oxygen was provided by introducing compressed air, with the air flow rate controlled at 1.0 L / min / L of the slurry. The pH of the slurry was adjusted and maintained at 9.5 ± 0.1 using a 10% sodium hydroxide solution. The leaching process was carried out at 25°C for 24 hours. Samples were taken every 6 hours to analyze the gold concentration in the leaching solution. After leaching, the slurry was filtered to obtain leachate and tailings. The gold concentration in the leachate was determined by atomic absorption spectrometry (AAS), and the residual gold in the tailings was determined by fire assay. The results showed that after 24 hours of leaching, the gold concentration in the leachate reached 1.58 mg / L, and the residual gold in the tailings was 0.25 g / ton. The calculated gold leaching rate was 95.45%. The gold extraction agent consumption was 1.8 kg / ton of ore.

[0058] Comparative Example 1: Traditional Sodium Cyanide Gold Extraction Process

[0059] This comparative example aims to compare the leaching effect of the traditional sodium cyanide gold extraction process under the same gold oxide ore conditions, so as to highlight the advantages of the novel environmentally friendly gold extraction agent of this invention.

[0060] Leaching experiment: The same gold oxide ore and grinding fineness as in Example 1 were used. The leaching conditions were consistent with Example 1, including the stirred tank, solid-liquid ratio (1:3), stirring rate (400 rpm), temperature (25°C), and leaching time (24 hours). Sodium cyanide (NaCN) was added to the slurry at a concentration of 0.5 g / L. To provide sufficient oxidant, 0.5 g / L calcium oxide (CaO) was added to the slurry as an activator, and compressed air was introduced at a flow rate controlled at 1.0 L / min / L of slurry. The pH of the slurry was adjusted and maintained at 10.5 ± 0.1 using lime slurry. Samples were taken every 6 hours during the leaching process to analyze the gold concentration in the leachate. After leaching, the slurry was filtered to obtain the leachate and tailings, and the gold content was determined separately. The results showed that after 24 hours of leaching, the gold concentration in the leachate reached 1.63 mg / L, and the residual gold in the tailings was 0.20 g / ton. The calculated gold leaching rate was 96.36%. The sodium cyanide consumption was 0.8 kg / ton of ore, and the lime consumption was 0.6 kg / ton of ore.

[0061] Comparative Example 2: Gold extraction process using unoxidized bio-based complexing agents

[0062] This comparative example aims to verify the importance of oxidative modification of organic complexing agents by oxidants in this invention.

[0063] Preparation of the gold extraction agent: The preparation process of the gold extraction agent in this comparative example omits the oxidant addition step S20. That is, after step S10 is completed, step S30 is directly performed, in which anhydrous sodium sulfate is added to the carboxymethyl oligodextrose solution and the reaction is heated. The parameters of the remaining steps S10, S30, and S40 are exactly the same as in Example 1. Finally, a powdered gold extraction agent without oxidation modification is obtained.

[0064] Application in Oxygenated Gold Ore: The same oxidized gold ore and grinding fineness as in Example 1 were used. The leaching experimental conditions were consistent with those in Example 1, including the stirred tank, solid-liquid ratio (1:3), stirring rate (400 rpm), temperature (25°C), aeration, and leaching time (24 hours). The unoxidized gold extractant was added to the slurry at a concentration of 2.0 g / L. The pH of the slurry was adjusted and maintained at 9.5 ± 0.1 using a 10% sodium hydroxide solution. After leaching, the gold content in the leachate and tailings was analyzed. The results showed that after 24 hours of leaching, the gold concentration in the leachate was 1.30 mg / L, and the residual gold in the tailings was 0.50 g / ton. The calculated gold leaching rate was 90.91%. The gold extractant consumption was 2.1 kg / ton of ore.

[0065] Data Comparison and Analysis:

[0066] The table below summarizes the main performance parameters of Example 1 and Comparative Examples 1 and 2 in the leaching of oxidized gold ore for intuitive comparison.

[0067]

[0068] The comparative data above clearly demonstrates that the novel environmentally friendly gold extraction agent prepared in this invention achieves a leaching efficiency comparable to that of the traditional sodium cyanide gold extraction process (95.45% vs. 96.36%), with only minor differences. However, it possesses fundamental advantages in environmental protection, completely avoiding the use and emission risks of highly toxic cyanide. Furthermore, the gold extraction agent of this invention exhibits an extremely rapid dissolution rate, significantly improving the ease of on-site preparation and application.

[0069] Compared to Comparative Example 2, the gold extraction agent of the present invention (Example 1), after modifying the bio-based complexing agent with an oxidant, significantly increased the gold leaching rate from 90.91% to 95.45%. This fully demonstrates the crucial role of the addition of the oxidant in step S20 and the precise control of pH and ORP in activating the organic complexing agent, increasing the density of active sites, and improving its complexing efficiency with alloy ions. The unmodified complexing agent, although possessing a certain complexing ability, had a lower number of active sites and lower complexing efficiency than the optimized gold extraction agent of the present invention, resulting in a decreased leaching rate and a slight increase in the consumption of the gold extraction agent. This further verifies the synergy and indispensability of each step in the preparation process of the present invention.

[0070] In summary, this invention, while considering environmental friendliness, achieves a refined gold extraction agent preparation process and optimized energy consumption. It also significantly improves leaching efficiency, dissolution rate, and applicability to various complex ores, constructing a highly efficient, economical, and environmentally friendly gold extraction technology solution with significant industrial application value and broad market prospects. The preparation method and product disclosed in this invention provide a landmark alternative for the field of gold hydrometallurgy, and are expected to drive the industry towards a safer, more environmentally friendly, and more efficient direction.

Claims

1. A method for preparing a novel environmentally friendly gold extraction agent, characterized in that, The process includes the following steps: S10: Dissolving an organic complexing agent in water to obtain an aqueous solution of the organic complexing agent, wherein the organic complexing agent is a bio-based compound containing carboxyl and hydroxyl functional groups in its molecular structure, and its weight-average molecular weight is 500 to 2000; S20: Adding an oxidant to the aqueous solution of the organic complexing agent, stirring evenly, and adjusting the pH value to 8 to 9 to form a mixed solution, wherein the oxidant is at least one of hydrogen peroxide or potassium permanganate, and the amount of the oxidant is 10% to 30% of the mass of the organic complexing agent; S30: Adding an inorganic salt auxiliary to the mixed solution, continuing to stir and heating to 40°C to 60°C, and reacting for 1 to 3 hours, wherein the inorganic salt auxiliary is at least one of sodium sulfate or potassium chloride, and the amount of the inorganic salt auxiliary is 50% to 100% of the mass of the organic complexing agent; and S40: Cooling the mixed solution after the reaction to room temperature and spray drying to obtain a novel powdered environmentally friendly gold extraction agent.

2. The preparation method according to claim 1, characterized in that, The purity of the organic complexing agent is not less than 95%, and the organic complexing agent is selected from oligosaccharide acids or their derivatives obtained by controlled degradation from natural biomass, including carboxymethyl oligodextrin, oxidized maltodextrin or modified lignin sulfonates within a specific molecular weight range.

3. The preparation method according to claim 2, characterized in that, The dissolution process in step S10 is carried out in a temperature range of 20°C to 40°C, with continuous stirring at a speed of 100 rpm to 300 rpm for 30 to 90 minutes, until a clear, transparent or slightly turbid homogeneous solution is formed. The conductivity of the water is less than 50 μS / cm, the initial concentration of the organic complexing agent in the water is 10% to 25%, and the carboxyl content and hydroxyl content in the organic complexing agent are 1.0 mmol / g to 3.0 mmol / g and 3.0 mmol / g to 6.0 mmol / g, respectively.

4. The preparation method according to claim 3, characterized in that, The preparation of the organic complexing agent in step S10 includes the following sub-steps: pre-treating agricultural and forestry waste and then performing mild hydrolysis or enzymatic hydrolysis to obtain a mixture of low molecular weight polysaccharides or their derivatives; subjecting the mixture to a selective oxidation reaction to introduce carboxyl functional groups while controlling the molecular weight distribution; and purifying the mixture using membrane separation techniques such as ultrafiltration or dialysis to obtain a product with a weight-average molecular weight of 500 to 2000 and a carboxyl and hydroxyl content that meets the requirements.

5. The preparation method according to claim 1, characterized in that, In step S20, the oxidant is a 30% hydrogen peroxide aqueous solution, and its amount is 15% to 25% of the mass of the organic complexing agent. The oxidant is added slowly and uniformly, and the stirring speed is maintained at 200 rpm to 400 rpm.

6. The preparation method according to claim 5, characterized in that, The pH value is adjusted by adding 20% ​​to 30% sodium hydroxide or potassium hydroxide aqueous solution. The pH value is precisely controlled by real-time monitoring and automatic replenishment using an online pH meter, with the error range controlled within ±0.1 pH units. In step S20, the addition of the oxidant is carried out under a precisely controlled redox potential. The ORP value rises and stabilizes at 200 mV to 400 mV vs. Ag / AgCl reference electrode after the addition of the oxidant.

7. The preparation method according to claim 1, characterized in that, The inorganic salt auxiliary in step S30 is analytical grade anhydrous sodium sulfate, and its amount is 70% to 90% of the mass of the organic complexing agent.

8. The preparation method according to claim 7, characterized in that, The heating process in step S30 is carried out in a reaction vessel with temperature control and stirring functions. Precise temperature control is achieved by jacket heating or electric heating, with temperature fluctuations not exceeding ±1℃. The stirring rate is adjusted to 300 rpm to 500 rpm. After the reaction is completed, the mixture is a uniform light yellow to brownish-yellow liquid with no obvious precipitation or stratification.

9. The preparation method according to claim 8, characterized in that, After the heating reaction in step S30 is completed, an additional filtration process is performed to remove insoluble substances or reaction byproducts. The filtration is performed using a microporous membrane with a diameter of 0.2 to 0.5 micrometers for precision filtration.

10. A novel environmentally friendly gold extraction agent, characterized in that: Prepared by any one of the methods of claims 1-9.

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