Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
1999-10-29
2001-12-04
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S743000, C075S744000
Reexamination Certificate
active
06325840
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the processing of zinc mine tailings to recover various components, including metals. More specifically, the present invention relates to the processing of zinc mine tailings to separate and remove the zinc powder, copper and various other semi-precious and precious metals without the use of any chemicals, and the integrated use of the separated carbon in an integrated cogeneration plant.
Zinc mine tailings are a product of the smelting of zinc, and often contain mixtures of coal, zinc powder, copper, lead and certain precious metals such as gold or silver. It has been estimated that zinc mine tailings contain up to 18% by volume of zinc and up to 28% by volume of copper. Nevertheless, because of the difficulty, expense and environmental hazards relating to the separation of these desired metals, no such separation is generally attempted. It is thus commonplace for zinc mine tailings to be simply piled and used as landfill. Unfortunately, this method of zinc mine tailing disposal often results in the leaching of copper, lead and other metals into the ground water.
Various methods of attempting to obtain valuable metals from zinc mine tailings are known in the prior art. However, the prior art methods involve the use of potentially dangerous and environmentally hazardous chemicals. Non-chemical methods of precious metal recovery using aqueous separation means are shown in U.S. Pat. No. 4,428,830. However, these aqueous systems are generally of the handheld variety and do not provide an industrial application as for an integrated cogeneration plant.
SUMMARY OF THE INVENTION
The present invention provides a process for treating zinc smelting by-products which permits the environmentally safe and cost effective separation of various metals therefrom. The process utilizes one or both of a series of wave tables or a cone separator, both of which use a recirculating water supply.
The zinc mine tailings which result from a smelting process are first mixed with water or air to create a slurry. This slurry is then moved over a series of wave tables which are set at varying specific gravities. The slurry is moved over a combination of weirs which are combined with the mechanical movement of the wave table, thus causing the water or air to move in such a manner that the fine metals rise.
Once the metals rise to the top of the water in the various wave tables, the separated metals are routed through chutes into individual containers. This system is based upon the specific gravities of the materials to be separated. The equipment is sized and adjusted to correspond to the specific gravities of each.
A cone separator may be used in place of, or in conjunction with the wave table apparatus. The cone separator is a cone-shaped device in which the zinc mine tailing slurry is placed. This cone-shaped device has the wide end at its top and its narrow end or point at the base. The cone separator moves the slurry around its inside periphery in an upward direction, to separation ports which are located at the upper portion of the cone separator. The cone separator also utilizes specific gravity and particle size to separate the various metal components of the slurry through chutes into individual containers. Additionally, the cone-shaped device employs recyclable water or air to suspend and carry the slurry through the process.
The slurry is thus subjected to one or both of the wave table or cone-shaped separator process to provide for the initial recovery of metals, including copper, zinc, lead, gold and silver. The gold and silver are retrieved in a concentrate form that requires further processing for extraction.
The material remaining from the slurry subsequent to the separation process is primarily the carbon portion of the zinc mine tailings. This remaining portion of the zinc mine tailings is dewatered then transported to the integrated cogeneration plant to be used as fuel for the production of electrical energy and to process steam.
Caloric values of various zinc mine tailings are usually in the broad range between 3,000 BTU/LB and 12,781 BTU/LB (MAF). To utilize this wide range of caloric value fuel, a boiler of known successful operation for the burning of lower grade coal products is used. The boiler system is built around a Pines Circulating Fluidized Bed System which is a hybrid between bubbling and circulating bed technology. This system is designed to optimize the dense-phase reaction of the combustion and sulfur absorption with low bed velocities in the bottom portion of the fluid bed, and to promote the lean-phase reactions of NOx reduction and co/char burnout in the fully entrained upper portion of the combustor.
Solids larger than fifteen (15) microns are separated in cyclones and are returned to the turbulent bed. Solids which are not separated by the cyclones are collected in one or both of downstream fabric filters and electrostatic precipitators. This system has a combustion at temperature levels whereby most of any remaining heavy metals will be encapsulated by the resultant ash. The energy generated by this process is used in part to produce steam, which drives the turbines which are used to heat or to generate electricity.
Subsequent to the burning of carbon in the system, the resultant ash may be again processed through the separation system to recover any remaining metals. Otherwise, the resultant ash can be redeposited on the cleaned-up smelter site to neutralize acid leaching. This ash could also be used by the cement industry for road beds.
The burning of the zinc mine tailings may also be performed without first performing the metal recovery/separation process. To do so, the zinc mine tailings are first crushed and then steam dried to raise the BTU value. These zinc mine tailings can then be placed in the cogeneration plant. The remaining material subsequent to burning can then be placed in the metal recovery/separation system. It is also possible to add lime to the zinc mine tailings to raise the alkaline content and encapsulate any heavy metals existing therein.
The present invention thus provides an environmentally safe method of disposing zinc mine tailings and recovering any existing valuable metals therefrom. This system employs no chemicals and requires no secondary fuel.
REFERENCES:
patent: 4428830 (1984-01-01), Hepfner et al.
patent: 4545963 (1985-10-01), Weir et al.
patent: 4708789 (1987-11-01), Cox
patent: 6103204 (2000-08-01), Lizama et al.
King Roy
McGuthry-Banks Tina
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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