Rhodium recovery: types of recovery and extraction methods for rhodium containing waste

What are the main sources of rhodium waste recycling? In the article, we discussed the main sources of rhodium waste. Next, we will discuss the breakdown of the types of rhodium waste recycling and the explanation of the extraction methods. Rhodium containing waste can be divided into four types:

1. Metal and alloy waste: thermocouple sensors and electroplating jewelry handicrafts, etc., in a dense wire shape. Most of them are alloys contaminated by other impurities or broken or damaged components, waste jewelry or leftovers produced during processing.

2. Rhodium containing catalysts: homogeneous catalysts of rhodium octanoate in pharmaceuticals and fine chemicals; Platinum palladium rhodium mesh catalysts in the nitric acid industry; There are many rhodium containing catalysts, such as automotive exhaust purification catalysts, catalytic hydrogenation in petrochemical industry, methanol carbonylation, hydroformylation of olefins, and other organic homogeneous catalysts.

3. Low grade waste slag: low grade waste slag refers to various waste slag produced in the use environment during the use of Platinum group devices due to high-temperature oxidation and volatilization, penetration, wear, entrapment and other reasons. There are furnace ashes of nitric acid industry, Fire brick of high temperature furnaces of glass fiber industry, glass slag and other industrial wastes containing precious metals.

4. Waste liquid containing Platinum group: rhodium containing waste solution from industrial production, platinum group waste water from electronic industry, plating solution and waste residue and plating solution from extraction metallurgy.

The extraction method for rhodium containing waste is briefly described as follows:

ammoniation

This method involves adding a large amount of ammonia water to a rhodochloric acid solution and reacting to form [Rh (NH3) 5Cl] Cl2. After filtration and precipitation, a sodium chloride solution is used for washing, and then it is dissolved in NaOH. It is acidified with hydrochloric acid and effectively treated with nitric acid, which can convert rhodium into a solution of [Rh (NH3) 5Cl] (NO3) 2. The solution is concentrated and converted into a rhodium chloride complex. After calcination, some soluble impurities are dissolved by boiling with dilute aqua regia, and then rhodium with a certain purity is obtained through hydrogen reduction. The ammonification method has a similar process principle to the above two methods, both of which introduce a third component precipitant to precipitate different forms of rhodium ions, and then separate and purify rhodium through refining. The advantage of ammoniation method lies in its low cost and simple process, making it a widely used method for depositing and refining rhodium.

Precipitation method

Precipitation method is one of the most widely used methods for rhodium purification, with simple operation and obvious effects. The main method is to use hydrolysis sedimentation or chemical reagent precipitation to achieve the recovery of rhodium. Firstly, the waste catalyst is concentrated using oxidation distillation method, keeping the mass fraction of rhodium between 0.1% and 0.7%. Then, oxygen or oxidant is introduced into it for oxidation treatment, lasting for 10-20 hours. Next, precipitation reaction is carried out. The precipitation method, as the most commonly used method in industrial production, has the advantages of simple operation and mature process, but it has high requirements for the types of impurities in the raw materials. When adjusting the pH value, it is easy to cause multiple ions to precipitate at the same time, resulting in a lower grade of precious metals in the precipitate.

Sodium nitrite method

This method is mainly to effectively treat the rhodium catalyst in the rhodochloric acid solution obtained after the pretreatment process. Under the action of Sodium nitrite, the base metal impurities in the rhodium containing solution can be completely removed. However, in the process of actual operation, the concentration of rhodium needs to be reasonably controlled. Generally, the concentration of rhodium needs to be kept at about 50g/L, and the temperature and pH value also need to be reasonably controlled. Generally, the temperature should be controlled between 80 ℃ -90 ℃, the pH value should be set between 1 and 1.5, and the solid Sodium nitrite should be put in through stirring. Based on this condition, rhodochloric acid ions can be converted into Nitroso rhodium ions in a timely manner, with strong solubility, Afterwards, a solution of Na2CO3: NaOH=(3:1) was used to adjust the pH value reasonably, followed by boiling for 30 minutes to 60 minutes. Through the above operation, the base metals can be converted into hydroxide precipitates, which can effectively separate rhodium. This method is often used for the separation and inspection of rhodium in analytical testing experiments, but due to the relatively high cost of NaNO3, its application in industry is relatively small.

Ion exchange and adsorption method

This method is mainly used to recover dissolved rhodium ions. Due to its high separation efficiency, simple equipment operation, and the ability of resins and adsorbents to be recycled and reused, it has very little impact on the environment. It is a green and environmentally friendly method for enrichment and separation, and has received attention, attention, and widespread application in the separation of precious metals.

Hydrogen reduction method

In order to obtain rhodium powder with high purity, a certain amount of rhodium black is placed in a tube furnace, connected to a gas pipe, and nitrogen is introduced to exhaust the air. Then hydrogen is introduced for heating treatment, with the temperature set at around 700 ℃ for 2 hours. After that, cooling treatment is carried out to cool the temperature to 400-500 ℃, nitrogen is introduced, and the gas is stopped after cooling to below 100 ℃. After lowering the temperature to indoor temperature, remove it and wash it with 37% hydrochloric acid. Wash the filtrate with deionized water to neutral and dry it in a vacuum environment to obtain rhodium powder with a certain purity, which has a significant effect.

Oxidation method

The oxidation method is also a method of recovering precious metals from waste precious metal catalysts. It mainly relies on the leaching of precious metals by strong oxidants to complete the dissolution and enrichment of precious metal ions, mainly consisting of chlorine gas, aqua regia, concentrated sulfuric acid, etc. This method has been widely used for the separation and purification of precious metals since the 1950s. However, due to the large amount of toxic and harmful gases such as nitrogen oxides and chlorine generated during the reaction process, it has gradually been replaced by other methods. For waste rhodium catalysts, due to the stable chemical properties of rhodium itself, it is difficult to dissolve in a strong oxidizing environment. It needs to be oxidized multiple times, resulting in a large amount of waste gas and low solubility, making it difficult for large-scale industrial dissolution, refining, and enrichment.

extraction method

The extraction method has the advantages of good separation efficiency and high recovery rate, mainly by using organic extractants in the aqueous phase to extract the pre treated rhodium coordination ions. However, rhodium not only exhibits different oxidation valence states in different oxidation environments, but also undergoes hydration or hydroxylation with environmental acidity, chloride ion concentration, etc., presenting cis, trans, or multinuclear structures. This chemical property makes it difficult to maintain stable valence states and species, which brings difficulties for extraction, separation, and purification. At present, Rh (III) is mainly separated through the use of TBP and TRPO, which means strict control of the valence state changes of rhodium before extraction and use, posing a challenge to industrial production. However, it is also expected to become a highly efficient method for separating and recovering rhodium in the future.

This article is only for reference and does not guarantee its accuracy or completeness. The above is a detailed answer to the questions about the types of rhodium containing waste recycling and extraction methods of Dingfeng Precious Metals.