Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-02-07
2001-10-02
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S714000, C210S724000, C210S726000, C210S737000, C210S911000, C210S915000, C423S286000, C423S490000
Reexamination Certificate
active
06296773
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for removing boron and fluoride ions from water generated in mine dewatering operations so the ultimate boron and fluoride levels meet stringent governmental environmental requirements for discharge of such water into surface streams.
As a particular example, water resulting from dewatering operations at gold mines in the Carlin trend area of Nevada, U.S.A. can contain dissolved boron concentrations on the order of about 1 mg/L, which due to environmental regulations must be reduced to about 0.6 mg/L or less before such water can be dispensed into the Humboldt River. Such water may also contain dissolved fluoride ion concentrations on the order of about 1.5 mg/L, which must be reduced to about 0.8 mg/L or less.
Prior attempts to remove boron from water by conventional water treatment methods such as treatment with aluminum sulfate, ferric salts, and lime have proved to be ineffective. Evaporation-crystallization processes and solvent extraction processes have been investigated. Ion exchange processes employing strong base ion exchange resins have been demonstrated to be effective, but remove other ionic species as well. As such, they are inefficient if boron is the only element to be removed. One resin, the ion specific resin for boron developed by Rohm & Haas Co., is also uneconomic for treatment of large volumes of water containing a low B concentration.
Mine dewatering operations are found in conjunction with, for example, gold recovery operations in the Carlin trend area of Nevada, U.S.A. Processes for the recovery of gold from refractory sulfide ores, “double refractory” ores containing sulfide and carbonaceous material, and other difficult ores such as those ores located in the Carlin trend employ pressure oxidation under acidic conditions as disclosed, for example, in Thomas et al. U.S. Pat. No. 5,071,477 and Thomas et al. U.S. Pat. No. 5,489,326 and/or, alternatively, a roasting operation. The products of such oxidation processes typically contain high acidic contents which must be neutralized before further processing by cyanidation as disclosed in the Thomas et al. patents, or by thiosulfate leaching in the manner disclosed in Marchbank et al. U.S. Pat. No. 5,536,297. There is a need, therefore, for an abundant source of neutralizing agent which is compatible with the gold recovery process in that it does not contain contaminants or other agents which substantially interfere with gold recovery, and which does not add substantially to the raw material requirements and disposal requirements for the overall operation.
SUMMARY OF THE INVENTION
Among the several objects of the invention, therefore, is to provide a water treatment process for reducing the boron content of water having a relatively low boron content down to a level of about 0.6 mg/L or less. Another object is to provide a process for reducing the fluoride ion content of water having a relatively low fluoride ion content down to a level of about 0.8 mg/L or less. Depending on site-specific requirements, another object is to utilize an alkaline sludge produced in the water treatment process for partially neutralizing acidic gold ore slurry from autoclaves or roasters in the context of gold recovery operations, otherwise the sludge would have to be disposed per applicable regulations.
Briefly, therefore, the invention is directed to a process for reducing boron and/or fluoride ion content of feed water containing boron. The pH of the feed water is adjusted in the presence of a source of magnesium in a concentration of between about 10 and about 80 mg magnesium per liter of feed water, to produce treated water and a magnesium precipitate containing boron and/or fluorine. The precipitate is separated from the treated water such that the treated water contains less than about 2 mg/L boron and/or less than about 0.9 mg/L fluoride ions. The magnesium is from a source selected from magnesium present in the feed water, magnesium added to the feed water in the form of a magnesium salt, and combinations thereof.
The invention is also directed to a process for reducing boron and/or fluoride ion content of water by contacting a quantity of feed water containing boron in the presence of magnesium and silicon with an alkaline hydroxide to produce treated water and a magnesium precipitate comprising an alkaline magnesium silicate containing boron and/or fluorine and separating the precipitate from the treated water such that the treated water has a reduced boron and/or fluoride ion content.
In another aspect, the invention is directed to a process for reducing boron and/or fluoride ion content of water, the process comprising adjusting, in the presence of magnesium, the pH of a quantity of feed water containing boron and/or fluoride ion at a temperature in the range of about 85° F. to about 130° F., to between about 10.2 and about 10.6 to produce treated water and a magnesium precipitate containing boron and/or fluorine, and separating the precipitate from the treated water to produce water having a reduced boron and/or fluoride ion content.
The invention is further directed to a process for reducing boron and/or fluoride ion content of water by adjusting the pH of a quantity of feed water containing boron in the presence of magnesium by contacting the water with an alkaline hydroxide in a contacting zone to produce treated water and a magnesium precipitate containing boron and/or fluorine, separating the treated water and precipitate into a substantially liquid fraction comprising treated water having a reduced boron and/or fluoride ion content and a substantially solid fraction comprising the precipitate, and transferring a portion of the solid fraction to the contacting zone to facilitate nucleation of said magnesium precipitate.
In another aspect, the invention is directed to an integrated process for reducing boron and/or fluoride ion content of water, and recovering gold from a refractory auriferous ore containing sulfide sulfur. The process includes contacting a quantity of feed water containing boron and/or fluoride ion in the presence of magnesium with an alkaline hydroxide to produce treated water and a magnesium precipitate containing boron and/or fluorine, and separating the treated water and precipitate into a substantially liquid fraction comprising water having a reduced boron and/or fluoride ion content and a substantially solid fraction comprising the precipitate. An aqueous slurry is formed of the refractory auriferous ore and subjected to pressure oxidation in an autoclave to produce an oxidized ore slurry, the pH of the oxidized slurry is raised by contacting the slurry with the substantially solid fraction containing the magnesium precipitate, and gold is recovered from the slurry.
The invention is further directed to an integrated process for reducing boron and/or fluoride ion content of water, and recovering gold from a refractory auriferous ore containing sulfide sulfur. A quantity of feed water containing boron and/or fluoride ion is contacted with an alkaline hydroxide in the presence of magnesium to produce treated water and a magnesium precipitate containing boron and/or fluorine. The treated water and precipitate are separated into a substantially liquid fraction comprising water having a reduced boron and/or fluoride ion content and a substantially solid fraction comprising the precipitate. A refractory ore is subjected to roasting in a roaster to produce a roaster calcine. An aqueous slurry is formed from the roaster icalcine, and the pH of the calcine is raised by contacting the calcine with the substantially solid fraction containing the magnesium precipitate, and gold is recovered from the calcine.
The invention is also directed to an integrated process for reducing boron and fluoride ion content of water, and recovering gold from a refractory auriferous ore containing sulfide sulfur. In the process a quantity of feed water containing greater than 0.8 mg/L boron and greater than 1 mg/L fluoride ion at a temperature in the rang
Kargel Reinhard
McMullen Jacques
Tsu Wilson
Barrick Gold Corporation
Hruskoci Peter A.
Senniger Powers Leavitt & Roedel
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