Recovery of Platinum and Palladium from Spent Catalysts:

1、Precious Metal Dissolution Method: Using high-temperature roasting, leaching with hydrochloric acid and oxidant, zinc powder displacement, dissolution with hydrochloric acid and oxidant, precipitation of platinum with solid ammonium chloride, and calcination to obtain pure platinum. The product platinum purity is 99.9% and the recovery rate is 97.8%.

2、Total Melting Leaching Method: Ion exchange adsorption of platinum (or palladium). The recovery rate of platinum is >98%, the recovery rate of palladium is >97%, and the product purity is all >99.95%. It has been applied in several factories.

3、Recovery of Palladium from Spent Palladium-Carbon Catalysts: The spent catalyst undergoes carbon burning, chlorination leaching, ammonia complexation, acidification purification, and finally reduction with hydrazine hydrate to obtain sponge palladium with purity >99.95%. A small amount of palladium in waste liquids such as complexation slag is recovered by resin adsorption. The recovery rate of palladium is >98%.

In the recovery and refining of spent palladium-carbon catalysts, the main purification methods are incineration and leaching.

Among them, the incineration method involves enriching the palladium-containing catalyst through high-temperature treatment, followed by recovery using traditional methods. The other is the leaching purification process, which utilizes ion exchange, electrolysis or displacement techniques to treat spent palladium-carbon. This method is generally suitable for spent palladium-carbon containing various other base metal impurities.

Here, we will share a refining process that combines incineration and leaching methods. First, the spent palladium-carbon catalyst to be refined undergoes evaporation and drying treatment, as used spent palladium-carbon contains a large amount of moisture. After drying, it is calcined at a high temperature of 600°C to remove the activated carbon components and organic matter from the spent palladium-carbon. Once calcination is complete, it is cooled to room temperature to obtain palladium oxide powder.

Palladium catalysts are widely used in chemical synthesis and industrial production. However, palladium is a precious metal, so recycling used palladium catalysts is becoming increasingly important.

Dissolution method and pyrometallurgical smelting are two commonly used methods. The dissolution method, often referred to as hydrometallurgy, is generally divided into three types: carrier dissolution method, selective dissolution method, and total dissolution method. Below is a brief introduction to these three methods:

1、Carrier Dissolution Method:Literally, this method completely dissolves the carrier using acid or alkali, then extracts precious metals from the residue left after dissolution. For example, most industrial carrier catalysts use alumina as the carrier. Direct pyrometallurgical purification is not feasible for this type of palladium catalyst—only by dissolving the carrier (utilizing its solubility with the corresponding acid) can palladium remain in the residue (since palladium is insoluble). The palladium is then extracted via dissolving and reducing the residue. This method has a high recovery rate but involves complex operations, and the carrier cannot be recycled.

2、Selective Dissolution Method:This method does not damage the carrier; instead, it uses special solvents to separate precious metals like platinum and palladium from the carrier, followed by reduction treatment of the dissolved liquid. Opposite to the above method, the carrier is retained and recyclable. However, its drawbacks are obvious: platinum and palladium are not fully dissolved, leading to a relatively low recovery rate.

3、Total Dissolution Method:As the name implies, this method completely dissolves the spent platinum-carbon catalyst (including the carrier). Ion exchange resin is then used to adsorb platinum. The obtained alkaline desorption solution is acidified to precipitate platinum, which is finally refined into pure platinum.

Adsorption Separation and Extraction Method for Precious Metals

Adsorption separation is a separation and enrichment technique where an adsorbent captures one or more components from a mixture via exchange, physical adsorption, or chemical adsorption processes—driven by electrostatic interactions, van der Waals forces, or stronger chemical bonding. This enables the target component to be separated and concentrated from the mixture. After subsequent treatments, the target substance is detached from the adsorbent to facilitate accurate quantitative analysis in follow-up steps.

Compared with fire assay and coprecipitation methods, it has become an important separation and enrichment approach for precious metals due to its simplicity of operation, environmental friendliness, and low cost. Traditional adsorbents mainly include activated carbon and ion exchange resins, whose applications in precious metal separation are relatively well-established. This article focuses on introducing new adsorbents developed in recent years, which offer higher adsorption efficiency and better selectivity.

Methods for Extracting Copper from Copper Ore：

There are pyrometallurgical and hydrometallurgical methods for extracting copper from copper ore. Pyrometallurgy is the main approach for copper smelting; currently, 80% of the world’s primary copper is produced via this method. Hydrometallurgy, by contrast, features low cost, low energy consumption, minimal pollution, and suitability for processing low-grade and refractory complex ores.

Glycine, an organic acid, is environmentally friendly. Experiments were conducted to study copper leaching from a low-grade copper ore in Tongling, Anhui using glycine, aiming to explore a green and economic pathway for the effective recovery of low-grade copper ore.

Under atmospheric pressure and alkaline conditions, the copper leaching rate from the Tongling ore reached over 93% with glycine, while iron was inhibited and barely leached—achieving excellent separation of copper and iron. Glycine is non-toxic, pollution-free, and eco-friendly. This method can support the effective utilization of copper ore resources with low grade and high iron content.

1、Gold Electrolysis for Gold-Silver Separation:Suitable for gold-silver alloys with gold content >90%. Pure gold of 99.95%~99.996% purity is obtained via gold electrolysis. Silver is converted into silver chloride and collected in the anode bag, realizing gold-silver separation.

2、Gold Electrochemical Dissolution Method:Essentially the same as electrolysis, except the cathode is enclosed in an ion-exchange membrane (or unglazed crucible). Cations cannot deposit at the cathode and instead enter the solution; silver chloride remains in the anode bag.

3、Silver Electrolysis for Gold-Silver Separation:Applicable to gold-silver alloys with silver content >75%, gold content 0~25%, and few other impurities. Silver powder with purity >99.95% is obtained through silver electrolysis. Gold is collected in the anode bag, achieving gold-silver separation.

Copper anode slime is an insoluble solid produced at the anode during the electrolytic refining of blister copper. Its yield generally accounts for about 0.2% to 1% of the mass of blister copper anode plates, and it usually contains high levels of precious metals. According to relevant data, more than 60% of China's gold and silver production comes from copper-lead electrolytic anode slimes. Therefore, anode slime is an important secondary raw material for extracting rare and precious metals, attracting much attention from resource recyclers.

Copper anode slime typically has a particle size of 100-200 mesh and appears gray-black or light gray, with a relatively complex phase composition. Approximately 70% of copper exists in metallic form, while the rest is in copper compounds; silver mainly exists in elemental and compound forms; gold is mostly in free state; and platinum group metals (PGMs) are primarily in metallic or alloy state.

Main treatment methods for copper anode slime: The general process involves "pretreatment → separation of valuable and base metals → recovery of base metals → extraction and separation of precious metals". Currently, three processes are applied to pretreated anode slimes both domestically and internationally:

1. Traditional pyrometallurgical-electrolytic treatment;

2. Hydrometallurgical treatment;

3. Combined mineral processing and metallurgical treatment.

The gold content in ore is extremely low. To extract gold, the ore must first be crushed and ground to fine particles, followed by ore dressing processes to pre-concentrate or separate gold from the raw ore.

1、Flotation:Flotation achieves mineral separation based on the differences in surface physicochemical properties of minerals. Treated with flotation reagents, target minerals will selectively adhere to air bubbles and be separated from gangue minerals.

2、Chemical Dressing for Gold Extraction:Chemical dressing separates and recovers valuable components from raw ore or middlings via chemical or physicochemical means, taking advantage of the variances in chemical properties between ore minerals and gangue minerals.

3、Heap Leaching Production Process:The gold heap leaching process features simple operation, low capital investment, high profitability and quick commissioning, thus experiencing rapid growth in recent decades.

Solid-Liquid-Solid Hydrometallurgical Process for Dissolving Metals from Copper Sulfide Minerals and/or Concentrates

This is a solid-liquid-solid hydrometallurgical process that takes place under supersaturation conditions with the presence of hydrated and/or non-hydrated salts. It is achieved through deliberate and repeated cycles of drying and wetting steps, which intensify the chemical and physical phenomena on the minerals or concentrates, thereby triggering the crystallization, recrystallization, and release of copper during the non-stoichiometric decomposition of sulfides and the subsequent precipitation with chlorides.The process consists of three key steps:

1、Wetting

2、Drying and Supersaturation

3、Washing and Rewetting

All steps are conducted at temperatures ranging from 20 to 40 °C regardless of the redox potential. It minimizes water and acid consumption without requiring additional oxygen input.

This process enables reduced water and acid usage because sulfide conversion can occur solely in the presence of hydrated salts or with only minimal additions of acid and water. Moreover, it allows for less water consumption during agglomeration and/or agglomeration-curing steps. When hydrated salts are mixed with the minerals, the water molecules bound in hydrated salts pre-wet the ore particles, cutting down the amount of extra water that needs to be added during wetting, agglomeration and curing stages.

This process is also applicable to base metal sulfides including nickel, zinc, cobalt, lead, molybdenum and others, unaffected by the common impurities in sulfide minerals, such as the presence of arsenic.