Today, roughly 80% of all chemical products are manufactured with the help of catalysts. Among the various catalytic systems, precious metal catalysts hold a unique position, because they possess unrivalled characteristics for many different process applications.
Precious metal powder catalysts differentiate themselves from other process catalysts by their high catalytic performance (activity, selectivity and recyclability).
Precious metals by definition cannot be characterized as "cheap". This is why the commercial use of expensive precious metal catalysts can only be considered if the contained metals can be recovered for reuse in the manufacture of new catalysts. This is known as the "Precious Metal Cycle", which is described below in a general way. Degussa Catalysts has established a network of local refining partners in the regions where Degussa Catalysts is doing business.
The precious metal remains the property of the customer throughout the whole cycle. The advantage is that fluctuations in precious metal prices have little effect on the economics of the process. In addition, refining precious metal catalysts avoids problems associated with disposal of spent catalysts.
Unfortunately, every application of precious metal catalysts involves the loss of some of the metals. On average, the losses realized in most precious metal catalysis processes are 2 to 3%. Losses of 5% or more are considered high. With effective planning, these losses can be minimized. Nevertheless these small but inevitable losses must be replaced by the purchase of additional metal.
During the development of a catalytic process and the engineering of a production plant, the minimization of losses should be given close consideration. Advice from our experienced professional staff at an early stage will ensure you of cost savings throughout the entire scale-up as well as the final production process.
Minor precious metal losses are also realized during the refining of the catalyst. The magnitude of these losses depends on the condition of the spent catalyst and on the precious metal contained therein. The refining process employed is also an important factor.
Consulting with Degussa Catalysts' experts gives you the opportunity to quickly identify any possible weaknesses in an application or the handling of your catalyst, and an opportunity to reduce precious metal losses significantly.
The precious metal cycle begins with the conversion of pure metals into the metal salt solutions required for the production of catalysts. The customer purchases and receives the precious metal with the initial shipment of a fresh catalyst. After the catalyst has been used by the customer, we refine it to recover the precious metal contained. The refining process takes about 10 weeks. Thereafter the amount of precious metal has been determined and can be credited to the customer's metal weight account.
The cycle is complete when a fresh catalyst is manufactured for the customer using recovered precious metal. With each purchase and use of fresh catalyst this cycle is repeated. The amount of metal necessary for the cycle depends on the customer's catalyst demand and the frequency of orders.
A rule of thumb: with regular use of a precious metal powder catalyst, you only need to purchase about 30% of the annually required amount of precious metals in order to maintain the cycle.
Credit or cash: the precious metal account
After the refining settlement has been made, the recovered precious metal is then credited to the customer's metal account. It remains in this account until the customer orders fresh catalyst.
The customer always has the option to close his precious metal account by asking us to purchase the precious metal balance. The delivery of the physical metal or its transfer to another account are also alternatives.
The 3 major steps in the recovery process
- Careful homogenization and sampling
Spent catalysts in their received form contain widely varying distributions of precious metals. Representative samples cannot be taken without prior treatment of the catalyst.
The first step in the refining process is the homogenization of the material that is to treat in such a manner that representative samples of the whole can be taken for metal analysis.
This homogenization is achieved by burning the material in a controlled, environmentally sound manner. After burning, the resultant ash is screened and large particles are ground. Finally, the entire precious metal containing ash is thoroughly blended.
This truly homogeneous ash will now provide samples that show a consistent concentration of precious metals by sophisticated laboratory analysis.
- Reliable state-of-the-art analysis
In the analytical laboratories a variety of different analytic methods are employed to determine the concentration of precious metals in the ash.
In addition to the classical wet-chemical methods, Degussa utilizes the most advanced physical methods such as atomic adsorption, x-ray fluorescence and emission spectroscopy to ensure that the precious metal contents are completely revealed.
The results of analysis performed by these methods provide a solid foundation from which the settlement and metal credits are determined. The metal credits are "deposited" in a weight account established specifically for each customer.
3. Precious metal refining with optimum results
The results of our analysis determine the refining process in order to guarantee the maximum yield of precious metal from the ash.
"Rich" or high-grade ashes with precious metals concentrations of 15% or more are dissolved by means of wet chemical methods. The precious metals are then successively precipitated from the solutions as salts.
"Poor" or low-grade ashes with precious metals concentrations of less than 15 % undergo a pyrometallurgical treatment.
After pyrometallurgical treatment, the resulting metal also goes through a wet chemical treatment to separate the precious metals.
The last step, which takes us to our desired result, is a fine purification process. This process yields the precious metals in the form of sponge or powder with purities of 99.95% to 99.99%.
The cycle is complete.
