Abstract
A novel process, termed gel precipitation, has been developed for producing gels of insoluble metallic compounds from aqueous solution. Controlled additions of a solution of the metal, which also contains the dissolved gelling agent, are mixed with a solution of the precipitating reagent, e.g. ammonium hydroxide. The gel is formed by the association of the gelling agent, usually a polymeric organic material, with the phase normally precipitated and in its truest form probably consists of a molecular complex between the organic constituent and the metal compound. The gel forms rapidly on bringing the two solutions into contact and there is no tendency for the discrete particles to adhere or coalesce; all the metal ion is normally confined to the gel phase.
The outstanding characteristics of the process are its simplicity and versatility; it operates at normal temperature and requires only conventional chemical plant. It is particularly applicable to precipitating conditions that yield gelatinous precipitates, difficult to handle, such as oxide hydrates and hydroxides. By suitable control of the process, gels of various shapes such as spheres, rods, filaments, or granular particles may be produced. One application that appears to have an important potential is the preparation of metal powders from the more easily reducible oxides by direct gaseous reduction of the gel; alloy powders may similarly be prepared directly by starting with a mixed metal solution of the required composition. The production of iron powder from pickling-liquor wastes is considered and the economics discussed.
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