Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Water – sewage – or other waste water
Reexamination Certificate
1999-09-22
2001-10-30
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Water, sewage, or other waste water
C205S745000, C588S253000
Reexamination Certificate
active
06309533
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention is concerned with de-oxygenation of water, and the applicability of same to the treatment of acid mine drainage (AMD). AMD is caused when water passes through a body of sulphide mineral, in the presence of oxygen. AMD is usually associated with dumped waste sulphide tailings from mining operations, which have become exposed to the atmosphere. Often, the sulphide is pyrite (iron sulphide, FeS2), but the problem arises with other sulphides.
The sulphide is safe, i.e water infiltrating through the sulphide tailings does not pick up acidity, if oxygen is excluded. If oxygen is present, the pH of the water passing through the sulphide (and into the groundwater) can become as low as 2.
Often, sulphide tailings are kept safe by being kept under water; at least, that is the aim of the mine operators. However, keeping tailings safe by keeping them submerged is risky in that the water table might fall, or a tailings dam might fail, etc, not to mention the effects of earthquakes, landslides, etc whereby the sulphide can become exposed to atmospheric oxygen.
The invention is aimed at providing a low-cost, low-maintenance, system for rendering sulphide bodies safe, in the above sense. The invention is aimed at removing oxygen from water that will pass through the body of sulphide. The invention may also be applied in other fields where de-oxygenation is required.
THE PRIOR ART
The task of resubmerging a body of sulphide tailings that has become exposed can be prohibitively expensive, especially since the requirement might arise decades (or centuries) after the mine operators have departed.
Often, when sulphide has become exposed, the technique followed has been to ignore the sulphide itself, and rather to treat the resulting acidified water downstream. That is to say, the water is allowed to percolate through the exposed sulphide, and is allowed to enter the groundwater, but then the water is treated (i.e its acidity neutralised) as it enters streams and lakes, etc, or as it approaches a well or other sensitive area.
Attempts have been made to cover exposed bodies of tailings over with a waterproof cover, in the form of a sheet of plastic or other man-made waterproof material, and thus to channel precipitation water away from the sulphide. However, waterproof covers tend to start to leak after a few years. Covering the sulphide with a layer of soil and vegetation has also been done, but again with less than reliable results. Such systems, even at the low levels of reliability typically achieved, and despite their huge expense, have the disadvantage that the need for maintenance increases as the decades go by. The sulphide remains, more or less for ever, as a potential source of acidity, should the covering ever fail.
Patent publication U.S. Pat. No. 5,630,934 (Chesworth et al, May 1997) shows a system for making a galvanic electrolytic cell, by making a body of sulphide tailings into a cathode, creating an anode from a body of e.g scrap metal, and ensuring electrolytic continuity in the water between the two.
Patent publication WO-95/29129 (Giliham et al, November 1995) shows an electrolytic system for treating water, which involves the use of granular iron.
Patent publication U.S. Pat. No. 4,990,031 (Blowes et al, February 1991) shows a micro-biological system for de-oxygenating water, for protecting a sulphide body.
Patent publication WO-91/08176 (Gillham, November 1993) shows a system for lowering the redox potential of water, (i.e for de-oxygenating the water) by passing the water through granular iron.
Patent publication U.S. Pat. No. 4,561,948 (Stiller, December 1985) shows an electrolytic cell, which uses pyrite and iron as the electrodes, for the treatment of acidified water.
GENERAL FEATURES OF THE INVENTION
The invention lies in providing a layer comprising a mixture of grains (particles) of a sulphide mineral with grains of a material that lies on the more electro-positive side of the sulphide, in the electro-chemical series. Water infiltrating through this layer becomes de-oxygenated, as described and explained herein. The water then may be passed to substances which might lead to the release of toxic substances if exposed to oxygen.
The invention involves the process of cathode-protection. In this process electrons pass from the anode of a galvanic cell, via an electrical connection, to the cathode. The anode dissolves into the aqueous electrolytic solution of the cell, and is said to be sacrificial. The cathode is stabilised by the electrons flowing towards it, does not dissolve, and is said to be protected. In any cell having electrodes of materials that are separated in the electro-chemical series, the electro-positive anode material tends to go into solution (i.e to be sacrificed), thereby stabilising and protecting the electro-negative cathode material.
In the invention, the points of contact between the grains of the different materials serve as the conductors joining the electrodes of the cell.
REFERENCES:
patent: 5575927 (1996-11-01), Sivavec et al.
patent: 5630934 (1997-05-01), Chesworth et al.
Chesworth Ward
Shelp Gene Sidney
Anthony Asquith & Co.
ENPAR Technologies Inc.
Phasge Arun S,.
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