Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1992-02-21
1994-02-01
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C21B 1108
Patent
active
052828816
DESCRIPTION:
BRIEF SUMMARY
This invention provides a method for smelting of metallurgical waste materials containing iron compounds and associated toxic elements. The invention enables recovery of metal values from such materials and the production of environmentally acceptable slag product.
One form of waste material for which the present invention is suitable is the final residue from leaching calcine from an electrolytic zinc process. The residue may contain at least one of jarosite, goethite and other iron compounds. It also contains significant concentrations of heavy metals such as toxic elements zinc and lead, as well as toxic elements such as arsenic and cadmium, and valuable metals such as silver. The waste cannot be disposed of as land fill or stored in open dumps because the toxic elements are unacceptably high and are leachable under weathering conditions, resulting in contaminated ground water. For this reason most plants store the waste in ponds sealed with plastics linings, or other sealing means. With time, the sealing means can break down, resulting in leakage of solutions and contamination of ground waters.
Other forms of waste material able to be smelted in accordance with the present invention include clinker from zinc kiln roasting operations, and iron and steel plant flue dusts. These waste materials also contain iron compounds, as well as toxic elements such as detailed above. Like the electrolytic zinc process leach residue, the toxic elements of these other waste materials are such that they can not be disposed of because of environmental risk.
To maintain a clean environment there is a requirement for a process which avoids the need for the storage of these and similar waste materials and which can be used in an on-going operation to produce an environmentally acceptable product. Leaching processes have been developed to remove the toxic elements, but these are expensive to build and operate and do not produce a completely satisfactory final product.
Smelting processes have been tried over a period of time for these waste materials, but these have been costly to build and to operate because of the perceived need for two-stage processing. Both theoretically and practically it has been found that a single-stage processing of the waste materials in conventional furnace systems cannot remove all of the toxic components to the low-levels needed for compliance with safe environmental disposal of the final product. Smelting the materials under strongly reducing conditions can remove the zinc, lead and cadmium by volatilization reactions to sufficiently low levels, but the arsenic is not removed to low enough levels. This is because under strongly reducing conditions arsenic is stabilized in the form of speiss (iron arsenide containing base metals such as copper) or in solution in matte (iron sulphide containing base metals such as copper). This occurs not only with smelting under reducing conditions, but also with plasma arc furnace operations which necessarily are reducing. Smelting the materials under weakly reducing, neutral or oxidizing conditions removes arsenic and cadmium but does not remove zinc and lead to low enough levels.
Thus previously developed processes have been based on two stages of smelting. The first stage is an oxidizing stage, removing the arsenic together with cadmium, some zinc and most lead to produce a lead-rich fume and a slag which contains most of the zinc and much of the lead in the feed material. This stage, as generally proposed, has to be carried out in a suspension smelting furnace, such as a cyclone or Outokumpu flash reactor. However it can also be carried out in bath smelting reactors using tuyere injection from below or lance injection from above of fuel, air and/or oxygen, such as conventional zinc fuming furnaces and in reactors using a top submerged lance injection system.
The second stage involves the transfer of the slag from the oxidizing smelting system into a second furnace, or a different zone in the same furnace, which operates under strongly reducing conditions to
REFERENCES:
patent: 3734717 (1973-05-01), Seglin
patent: 5069715 (1991-12-01), Reid
Soviet Inventions Illustrated, Week 8429 (Aug 29, 1984) p. 11, SU A1 1054436, UST-Kamengorskij Revolyutsii Svintsovotsinkovyj Kombinatim V.I. Lenina.
Baldock Brian R.
Floyd John M.
Lightfoot Brian W.
Robilliard Kenneth R.
Ausmelt Pty. Ltd.
Rosenberg Peter D.
LandOfFree
Smelting of metallurgical waste materials containing iron compou does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Smelting of metallurgical waste materials containing iron compou, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Smelting of metallurgical waste materials containing iron compou will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-576807