Recovering precious metals
11 Nov 2003
A British-Swedish joint venture between Chematur Engineering and Johnson Matthey has developed a process that uses supercritical water oxidation to recover precious metals from catalysts.
The technology, called AquaCat, which is being deployed at Johnson Matthey's Brimsdown, UK facility, offers organic destruction efficiencies of close to 100%, but without any of the problems associated with incineration.
Up until now, the recovery of precious metals used as catalysts in chemical processes has involved the use of incineration. The AquaCat technology uses a process based on supercritical water oxidation which provides many environmental and economic benefits.
Precious metals are used extensively in catalysts which improve the efficiency of a wide range of industrial chemical processes. The metals used - platinum, palladium and rhodium - represent a huge investment and the rapid and economical recovery of the metal from spent catalyst is a vital part of their use.
The AquaCat process offers environmental improvements on incineration since it requires almost no external source of thermal energy, eliminates the need for expensive exhaust gas treatment, reduces the amount of physical handling of the material and makes containment easier.
According to an article in the June 2003 issue of 'Fitration and Separation' magazine, the majority of materials that come for catalyst recovery are heterogeneous in form. In the AquaCat recovery process, these heterogeneous materials are first made into a slurry in water. After sampling to determine precious metal content, the mixture is pumped to supercritical pressure and heated to supercritical temperature and transferred to a reactor. Oxygen is then added, and the organic backbone of the spent catalyst is immediately burnt off, leaving behind almost clean water containing a fine particulate phase of precious metal oxides. The solid precious metal oxides are then separated from the water, and are ready for refining and use in the preparation of fresh catalysts.
The AquaCat processing equipment can be installed at customer sites. This may be particularly important to the pharmaceutical or petrochemical industries where the residue is either highly bioactive or high in volume making handling and transport difficult.
In addition to the recovery of catalysts, the supercritical water oxidation process, which Chematur originally acquired from a Texan firm, Eco Waste Technologies, for an undisclosed sum, can also be used to treat municipal or drinking water sludge and waste streams containing valuable inorganic material.
