Production of Copper Powder by Hydrometallurgical Processing

Hydrometallurgical methods may be used to produce a number of metal powders, including copper, cobalt, and nickel. The basic processing steps consist of preparing pregnant liquor by leaching ore or another suitable raw material, followed by the precipitation of the metal from this solution. For copper, the most important precipitation methods are cementation, reduction with hydrogen or sulfur dioxide, and electrolysis. Use of several leach-precipitation steps or the inclusion of flotation, solvent extraction, or ion exchange improves the purity of the final material.

Despite several process development efforts in the 1950s and 1960s that led to radical improvements in purity and properties of hydrometallurgically produced copper powders, commercialization attempts in the United States have failed. Causes for this failure include the increasing cost of energy, coupled with the high energy requirements of some hydrometallurgical methods and the difficulty in economically producing powders with a wide range of properties suitable for various uses.

Cement copper, like other hydrometallurgically produced copper powders, has low apparent density and high specific surface area (1 m2/g). The particles are spongy, because they are agglomerates of very small primary particles (Fig. 23). Although cement copper often has higher green strength characteristics than most other copper powders, its sintering activity, when used alone or in 90/10 bronze, is inferior because of the presence of finely divided, unreducible aluminum and silicon oxides. The primary use of cement copper is in composite friction material applications.

Fig. 23 Scanning electron micrograph of cement copper Leaching

The leaching of copper oxide and copper sulfide ores entails partial dissolution to cupric sulfate (CuSO4) with sulfuric acid (H2SO4) plus iron sulfate (FeSO4). The presence of pyrite (FeS2) in many ore deposits, and its reaction with water and oxygen to form iron sulfate and sulfuric acid, represents an important source of acid. In dump leaching, the pH of the leach solution is maintained between 1.5 and 3.0, partly to protect bacteria that promote and accelerate the oxidation of pyrite and sulfidic copper minerals and also to avoid hydrolysis of iron salts.

The copper content of the pregnant solutions varies from less than 1 g/L (0.15 oz/gal) to several grams per liter (ounces per gallon); for vat leaching, it can be much higher. Other leaching methods include ammonia leaching, which is used for certain copper oxide ores, and the so-called leach-precipitation-flotation method, which is applied to mixed oxide sulfide ores.

0 0

Post a comment