Liquid purification or separation – Structural installation – Geographic
Reexamination Certificate
2000-01-18
2001-02-27
Simmons, David A. (Department: 1724)
Liquid purification or separation
Structural installation
Geographic
C210S205000, C210S290000, C166S105000, C299S005000
Reexamination Certificate
active
06193881
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the recovery of valuable metals and mineral salts from mineral bearing host rocks and to the purification of mineral salts formed by evaporation of natural brines.
Valuable metals are found in nature in mineral-bearing host rocks. Ores must be processed physically and chemically to produce commercial products. Normally the ores are mined underground, and then refined in factories on the surface. In order to economize on the mining cost and to minimize the environmental impacts, in-situ mining methods have been devised.
In recovery by in-situ mining of valuable metals such as the Carlin (Nevada) type of organic-rich metalliferous rocks containing appreciable amounts of disseminated gold and associated metals such as mercury, arsenic, antimony etc., or metalliferous black-shale deposits, containing uranium, gold, silver, copper, lead, zinc, and nickel etc., the problem is two-fold: the host rock has to be oxidized and it has to be made permeable for leaching solution.
Processes are known for recovery of disseminated metals in organic-rich shale, such as gold in deposits of the Carlin type, where ores are mined and milled before they are subjected to oxidation at high temperature are known. These process are commonly referred to as “shale-burning”. Co-pending patent application Ser. No. 08/403,364 discloses a method to oxidize organic-rich shale by currently available methods of shale burning, before injecting leaching fluid into the burnt rock.
The currently available methods of in-situ shale burning have, however, two disadvantages:
(1) Porosity and permeability for shale to be burnt originate from the collapse of a roof above an excavated cavity. The cost of such excavation renders the process uneconomical.
(2) The fracturing of rubblized and burnt rock causes the leaching fluid to flow through fractures rather than pervasively through the whole rock. Such a flow pattern does not permit the leaching of metals from the largely intact sections of host rock which are not pulverized or not very minutely fractured.
The currently available methods of in-situ leaching metals from host rock have a disadvantage:
(1) The leaching solution must flow laterally through a porous and permeable host rock, and economic values cannot be leached out from a relatively impermeable host rock by such lateral flow of leaching solution.
It is an object of the present invention to improve control of chemical reactions in leaching metals and to recover valuable constituents at greater depths than now possible.
Humid regions with high groundwater table or arid regions with low groundwater table can be dealt with, because the hydrologic cell is designed to minimize lateral losses to natural groundwaters. Vertical flow through relatively impermeable bed is induced to flow from a lower aquifer upward to an upper aquifer or other collecting devices for reacted solution.
SUMMARY OF THE INVENTION
The present invention designs hydrologic cells so that fluid can be injected into a source aquifer before it seeps into a relatively impermeable host rock for shale-burning or for leaching of metals, and then be recovered by flowing into a sink aquifer located on the side of the body of host rock opposite the side on which the source aquifer is located.
Valuable salts have been produced by evaporation of brines in nature. However, the salts may contain considerable impurities which need to be processed physically and chemically to produce useful commercial products. The present invention designs in-situ reactors with hydrologic cell so that salts precipitated from brines can be purified economically.
Recovery of Economic Values from Host Rock with in-situ Chemical Process Underground
Currently, available underground in-situ methods, used to extract copper and uranium most successfully, encounter problems in controlling water-flow through the metal-bearing host rock. Fluids find paths of least resistance, along fractures and around fragments, which diminish the efficiency of metal extraction to about 10% recovery. Controlling the rate and amount of fluids along natural aquifers so that it flows into target areas of rocks is difficult. Rock bodies such as the Carlin type of deposits, attractive as economic targets, have undesirable physical or chemical properties, which must be modified to be processed by in-situ methods.
It is not desired to force the fluids directly into the target volume of rock, but rather to introduce them into a porous and permeable aquifer, from which they seep through and reacts with the relatively impermeable host-rock, and then flow into another porous and permeable aquifer, from which the fluid can be drained or pumped out via an exhaust borehole and moved into a factory or a facility for further processing.
Where natural aquifers cannot be used, an artificial aquifer may be constructed below and above the host rock containing mineralized zones by first using the currently available methods of hydraulic fracturing to produce fracture surfaces, and then injecting particulate matter to make an artificial bed porous and permeable to fluid flow. The pressure in the lower aquifer is raised when fluid is injected under pressure from the surface to the source aquifer, and the pressure of the upper aquifer is hydrostatic or lower when fluid is being pumped out of the sink aquifer. A hydraulic potential gradient is thus established between the source and sink aquifers. The linear rate of fluid flow through relatively impermeable mineralized zones of host rock can be adjusted by varying the pressures in the two aquifers. The volume rate of fluid flow through relatively impermeable mineralized zones of host rock can be adjusted by varying the cross-sectional area of the host rock perpendicular to the direction of the fluid flow. An adequate volume of fluid can thus be induced to seep pervasively through a relatively impermeable rock.
The rate and the temperature of the chemical reaction between the injected fluid and the host rock are adjusted by injecting fluid of a given composition needed for processing rock bodies or for leaching out metals. For oxidation processes involving carbon and/or organic matter in host rock, the temperature of shale burning can be adjusted by injecting a fluid with a suitable oxygen content. For other chemical processes, involving neutralizing of pore fluids or leaching of host rock, fluid of suitable composition is injected.
Reacted fluids flowing into the upper aquifer are transferred to the surface for further processing. The thermal energy of the hot fluids may be used to produce steam to drive turbines and produce electricity. Fluids containing toxic substances can be guided to plants for detoxification. Fluids containing dissolved metals can be transferred to factories for conventional extraction of valuable components.
With the installation of source and sink aquifers, a large volume of fluid can flow through and penetrate target rock under conditions that can be controlled at the surface. Because of the large cross-sectional area of fluid flow through a layered host rock, huge volumes of fluid can be passed through rocks at rates designed to optimize the efficiency of the chemical reaction, such as shale burning, oxidation, leaching, etc.
Design of in-situ reactors takes into account geometric and geochemical characteristics of individual mineral rock bodies.
Purification of Salts Produced by Evaporation of Brines by in-situ Chemical Reactions Near Surface
In producing salts by solar evaporation, the processes are, in numerous instances, not controlled to produce products of desirable purity. Magnesium salt bischoffite MgCL
2
.6H
2
O precipitated from brines in arid regions, for example, may not be suitable for hydrolysis to produce metallic magnesium because of the presence of small amounts of sulfate, boron, and/or other compounds as impurities. Potash salt KCl precipitated from brines in arid regions may not be marketable as fertilizer because of the presence of NaCl (up to 20%) as impurities.
For the purpose
Helfgott & Karas P.C.
Prince Fred
Simmons David A.
Tarim Associates for Scientific Mineral and Oil Exploration AG.
LandOfFree
In-situ chemical reactor for recovery of metals or... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with In-situ chemical reactor for recovery of metals or..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and In-situ chemical reactor for recovery of metals or... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2571690