Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing single metal
Reexamination Certificate
1999-11-24
2001-11-20
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing single metal
C075S731000
Reexamination Certificate
active
06319389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the treatment of ores containing leachable metal values. More specifically, this invention relates to the recovery of copper values from copper ores, and is particularly applicable to leaching of secondary copper sulfides from any copper sulfide deposit and extraction of copper therefrom. In a preferred embodiment, the invention relates to a hydrometallurgical treatment of sulfide minerals found in porphyry ore deposits, which are generally difficult to leach in an efficient and economical manner.
2. Description of the Prior Art
In treating copper bearing ores, materials containing primary or secondary sulfides have typically been processed using the conventional milling/flotation process which includes crushing, grinding and flotation, followed by smelting and refining of the concentrate. Copper oxide minerals are not easily floated and these ores have generally been processed hydrometallurgically by sulfuric acid leaching in slurry, vat or heap leaching processes. In recent years, bio-heap hydrometallurgical processing of secondary sulfides ores using a ferric sulfate lixiviant has gained some favor. Research has also been intense in recent years on leaching of copper sulfide concentrates, including chalcopyrite concentrates, using slurry bio-leaching, atmospheric leaching of ultra-fine ground concentrates and processes involving pressure leaching at elevated temperatures.
Conventional milling/flotation typically requires a particle size reduction to less than 150 mesh (0.105 millimeters) to achieve mineral liberation from the gangue and to permit high rougher flotation copper recovery. Regrinding of the rougher concentrate produced to as fine as minus 400 mesh (0.037 millimeters) may then be necessary to allow mineral liberation sufficient to achieve an economic concentrate grade. The concentrate produced must then be further processed by smelting and refining or a hydrometallurgical process to finally obtain cathode copper. The conventional milling/flotation process is mineralogy dependent, and is energy, capital and operating cost intensive, as are the subsequent smelting and refining steps, requiring a higher ore grade to justify project economics.
Hydrometallurgical leaching processes for ores of copper oxides, secondary sulfides and dump leaching of chalcopyrite waste materials have typically included in situ leaching, dump leaching, heap leaching, vat leaching and agitation slurry leaching.
In situ leaching processes involve in-place leaching of material in a deposit. Porosity for solution permeability is required either naturally, by high pressure, hyro-fracturing, or by blasting. Rubble zones or caved areas from old underground mines are also suitable for in-situ or in-place leaching. Solution is distributed on the surface or injected through drill holes in the deposit, percolates or is forced by pressure through the ore zone, solubilizing the metal values. The leach solutions are collected by underground workings or drill wells for recovery of the metal values therefrom. Typically, recovery of metal values requires years and only reaches leach recoveries of 40 to 60 percent.
Dump leaching is typically applied to leaching of the massive run of mine tonnages of mineralized, but below ore cutoff grade waste, generated from copper porphyry deposit mine operations. Dump leaching can be used to recover copper from materials containing oxide and sulfide mineralization and utilizes bio-leaching techniques. Recoveries are typically less than 50 percent after 10 to 25 years of leaching. Leach kinetics are very slow and solution copper contents are very low.
Heap leaching is applied for leaching of oxidized copper ores, secondary copper sulfides, uranium and precious metal ores. Typically the ores are crushed to less than one inch (25 millimeters) and to as fine as minus ¼ inch (6.3 millimeters). Leaching can be performed in permanent heaps where successive lifts are placed over the original lift or in a reusable pad which allows the ore to be leached in one lift, the leach residue and a new lift placed on the pad. Recoveries are generally 65 to 85 percent, depending or the ore being leached, and leach cycle times range from months to a year. Heap leaching has been used more recently for bio-leaching of secondary copper sulfide ores such as with the operations of Quebrada Blanca and Cerro Colorado in Chile and Cerro Verde in Peru. Cyprus Miami in Arizona, USA, and other US producers also employ a ferric leach or ferric cure technology for run of mine mixed oxide and secondary sulfide copper ores. Heap leaching technology allows processing of higher grade ores, but is typically used on lower grade ores (less than 1% copper) due to comparatively low capital and operating costs versus conventional technology.
Heap leaching of secondary copper sulfides of chalcocite and covellite is a viable but challenging hydrometallurgical process. The dedicated secondary sulfide leaching facilities started up over the past few years have generally experienced lower recoveries, slower leach kinetics and higher operating costs than predicted from test work. The major difficulty has been oxygen availability internally within the heap sufficient to promote bacterial activity for direct leaching of sulfides and/or the oxidation of ferrous sulfate to ferric sulfate, the primary lixiviant for the process. Many techniques from fine crushing to drum agglomeration, various lift heights, various flow rates and flow regimes and forced aeration have been employed to enhance the process. The end result remains that this technology has distinct limitations and disadvantages.
Slurry agitated leaching has been used primarily on oxidized copper ores. It can also be used for bio-leaching of copper sulfide concentrates. Slurry leaching requires fine grinding and continuous agitation which results in high power consumption and is typically applied to higher grade ores or concentrates.
Vat leaching has typically been used for processing of copper oxide ores and those ores with higher copper grades.
Although the present invention is equally effective on any leachable copper containing ore, it is particularly effective on leaching of the lower grade secondary sulfide copper ores commonly found in porphyry copper deposits.
It is well known that the bulk of the world copper resources are contained in porphyry copper deposits. Porphyry deposits originate as intrusions of protore, generally with chalcopyrite mineralization. When rock porosity is present to allow downward flow of meteoric water, and provided sufficient pyrite is present to produce oxidizing acids, surface minerals are dissolved and transported downward to areas where solutions become more basic and reducing, generally below the water table, and are reprecipitated. Thus, there are typically three copper mineralized zones in classical porphyry deposit, the oxidized zone, the supergene zone (which is generally the highest grade zone in the deposit that contains secondary sulfide minerals) and the hypogene zone or protore zone which is presumably the original source of all the copper in the deposit.
Thus, a classical description of a porphyry copper deposit includes a relatively copper barren oxidized capping over the deposit; lying beneath this capping is a zone of oxidized copper mineralization (oxide copper ore); beneath this zone is a zone of enriched secondary sulfides; and beneath the secondary sulfides zone lies the zone of primary sulfides or protore from which the deposit was generated.
Porphyry deposits can deviate from the classical model due to age of the deposit, mineralization, ground water table variations over time, erosion, climatic conditions, etc. Thus, deposits can have little to no oxide capping or a large oxidized capping zone, and little or no secondary sulfide enrichment or large enrichment zones. The majority of the in ground copper resources worldwide are contained in primary ore zones as chalcopyrite (70%). However, substantial resources
Fountain Gearld F.
Keane Joseph M.
Hydromet Systems, L.L.C.
Valentine Donald R.
Ware Fressola Van der Sluys & Adolphson LLP
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