Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-05-21
2001-03-20
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C209S005000, C210S727000, C210S728000, C210S730000, C210S734000, C210S731000, C210S735000, C210S736000
Reexamination Certificate
active
06203711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for clarification of substantially aqueous fluids, such as process streams, and more particularly to separation of particulate materials from inorganic materials and mineral processing operations, such as processing of ores, clays, coal, as well as byproducts from metal and metal salt processing.
2. Description of the Related Art
Aqueous fluids are present in many industrial processing operations such as mining and mineral processing, for example, as aqueous streams containing dispersed solids that cannot be separated completely by simple sedimentation or filtration. The presence of the dispersed solids causes the fluids to be turbid, i. e., appear cloudy and/or opaque. Examples of such fluids include wastewaters from mining of ores, minerals, and precious metals, certain chemical processing plants, e. g., production of clays, alumina, pigments and paints, as well as polishing operations e. g., sheet metal and silicon wafers. Large volumes of aqueous fluids, many of which are turbid, are typically circulated through processing operations for these industries.
Problems associated with such fluids include corrosion and scaling of equipment, for example, pumping systems; loss of product values in the suspended solids; and low product quality due to poor solids removal. Such fluids may need to be treated prior to discharge from a plant or if the water content of the fluid is to be recycled.
Any aqueous fluid being discharged from a manufacturing plant to a public water system must meet local requirements. While there has been much attention devoted to the general area of wastewater treatment and, more specifically treatment of municipal wastewaters, such treatment methods may not be effective for industrial processing wastewaters in terms of cost or providing acceptable water quality. Therefore, there is a need for an efficient, cost-effective system to clarify wastewater fluids present in inorganic and mineral processing.
SUMMARY OF THE INVENTION
The present invention provides a process, which can be used for example, for clarification of a substantially aqueous fluid comprising suspended particulate material. The process comprises:
(a) contacting with the aqueous fluid:
(1) an anionic silica-based colloid having an S value of less than 50%; and
(2) an organic polymer selected from the group consisting of a cationic organic polymer, an amphoteric organic polymer, and mixtures thereof; whereby flocculated material is produced; and optionally
(b) separating the flocculated material from the fluid.
DETAILED DESCRIPTION
Materials
Aqueous Fluid
In the process of this invention, the aqueous fluid to be treated can be from any inorganic materials or minerals processing plant that produces a substantially aqueous fluid comprising suspended particulate material. This process is useful in treating aqueous fluids in conventional mining and mineral processing operations including aqueous fluids derived from mining of precious metals, base metals, ores, clays, and coal. This process is useful in treating fluids derived from the beneficiation of ores. This process is useful to treat fluids derived from drilling operations, such as oil drilling, including drilling muds, which may also contain suspended organic materials. Further, this process is useful in treating aqueous fluids containing suspended materials derived from processing of inorganic materials such as clays, alumina, pigments and dyes. Still further, this invention is useful in treating aqueous fluids derived from polishing operations such as polishing of sheet metal, for example, steel, and silicon wafers.
While the aqueous fluid can generally be considered as a stream containing suspended material flowing through a plant operation, the fluid can also be considered a stationary fluid, for example a still pond.
It should be recognized that the suspended particulate material in the aqueous fluid to be treated, especially fluids derived from mining and mineral processing operations, may be comprised of inorganic or organic components, or mixtures thereof. For example, organic components may include humates, which are naturally found in soils and mined materials.
Anionic Silica-Based Colloid
Anionic silica-based colloids useful in the process of this invention should have an S value of less than about 50%, as defined in Iler and Dalton in
J. Phys. Chem.,
1956, vol. 60, pp. 955-957. The S value is a measure of the degree of aggregate or microgel formation and a lower S value indicates a higher microgel content and is determined by the measure of the amount of silica, in weight percent, in the disperse phase. The disperse phase consists of particles of anhydrous silica together with any water that is immobilized at the surface or in the interior of the particles.
Examples of anionic silica-based colloids which can be used in the process of this invention include polysilicic acid, polysilicic acid microgels, polysilicate microgels, polyaluminosilicate microgels, colloidal silicas with a high microgel content, and mixtures thereof, such that the colloid has an S value of less than about 50% and preferably less than 40%. These colloids are distinct from many colloidal silicas in that these colloids usually have surface areas of 1000 m
2
/g or higher and the microgels are comprised of small 1 to 2 nm diameter silica particles linked together into chains and three-dimensional networks.
Polysilicate microgels, also known as active silicas, have SiO
2
:Na
2
O ratios of 4:1 to about 25:1, and are discussed on pages 174-176 and 225-234 of “The Chemistry of Silica” by Ralph K. Iler, published by John Wiley and Sons, N.Y., 1979. Polysilicic acid generally refers to those silicic acids that have been formed and partially polymerized in the pH range 1-4 and comprise silica particles generally smaller than 4 nm diameter, which thereafter polymerize into chains and three-dimensional networks. Polysilicic acid can be prepared, for example, in accordance with the methods disclosed in U.S. Pat. No. 5,127,994, incorporated herein by reference.
Polyaluminosilicates are polysilicate or polysilicic acid microgels in which aluminum has been incorporated within the particles, on the surface of the particles, or both. Polysilicate microgels, polyaluminosilicate microgels and polysilicic acid can be prepared and stabilized at acidic pH. Polyaluminosilicates are particularly useful at low pH.
The polysilicate microgels and polyaluminosilicate microgels useful in this invention are commonly formed by the activation of an alkali metal silicate under conditions described in U.S. Pat. Nos. 4,954,220 and 4,927,498, incorporated herein by reference. However, other methods can also be employed. For example, polyaluminosilicates can be formed by the acidification of silicate with mineral acids containing dissolved aluminum salts as described in U.S. Pat. No. 5,482,693, incorporated herein by reference. Alumina/silica microgels can be formed by the acidification of silicate with an excess of alum, as described in U.S. Pat. No. 2,234,285, incorporated herein by reference.
In the process of this invention, better results have been generally found to occur with larger microgel sizes, generally greater than 10 nm size microgels give the best performance. Microgel size can be increased by any method known to one skilled in the art, such as aging of the microgel, changing pH, or changing concentrations during microgel formation.
In addition to silica microgels, silica sols such as those described in European patents EP 491879 and EP 502089 can also be used for the anionic silica-based colloid in this invention. In EP 491879 is described a silica sol having an S value in the range of 8 to 45% wherein the silica particles have a specific surface area of 750 to 1000 m
2
/g, which have been surface modified with 2 to 25% alumina. In EP 502089 is described a silica sol having a molar ratio of SiO
2
to M
2
O, wherein M is an alkali metal ion and/or an ammonium ion of 6:1 to 12:1 and containin
E. I. Du Pont de Nemours and Company
Hruskoci Peter A.
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