Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1996-01-04
1997-12-30
Hruskoci, Peter A.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210724, 210747, 210749, 210170, 210192, 2101981, 210206, 2102421, 210906, 210912, 422265, 422271, 422272, C02F 158
Patent
active
057026149
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to methods of improving the quality of fluids.
BACKGROUND TO THE INVENTION
There is a continual need for more efficient and effective methods for treating and improving the quality of water. Increasingly stringent waste water standards demand that contaminated liquid effluent from mining, quarrying, processing, manufacturing or agricultural operations be adequately treated prior to release.
Sulphate and/or phosphate polluted water are typical examples of fluids requiring treatment. Acid-sulphate water is generated by a variety of mining/quarrying operations and other industrial processes. Such water constitutes a hazard due to its low pH (high acidity) and the concomitant high concentrations of toxic inorganic components (e.g. arsenic, cadmium, iron, copper, lead, zinc, cobalt, aluminium, manganese and nickel . . . etc). These contaminants may render the water unsafe for domestic or livestock consumption and irrigation purposes, and unsuitable for release into rivers, sewers or storm-water systems. Phosphate-enriched water can be generated by natural drainage from land subjected to modern agricultural practices, and is also derived from human and animal sewage/effluent; excess water-borne phosphate can encourage the growth of toxic algal blooms.
Calcium-based water treatment compounds such as calcium carbonate, calcium oxide (lime) and calcium hydroxide are amongst the most common, inexpensive and useful water treatment agents for both sulphate and phosphate enriched waters.
For example, one approach to the treatment
eutralisation of acid-sulphate water involves the addition of calcium hydroxide (Ca(OH).sub.2) or calcium oxide (CaO) and may be represented by the following reactions; ##STR1##
The dissolution of calcium hydroxide or calcium oxide in acid-sulphate water not only increases its pH to more acceptable levels, but simultaneously lowers the concentration of toxic metal components. This is achieved by the co-precipitation of a range of metals (commonly as hydroxide compounds) with the gypsum (calcium sulphate).
These neutralisation reactions are generally extremely rapid, and thin but impermeable rinds or precipitates of compounds such as gypsum and co-deposited metal hydroxides can readily coat the surfaces of particles of treatment reagents such as calcium oxide, calcium hydroxide or calcium carbonate. These coatings can prevent total dissolution of the calcic compounds, thereby dramatically diminishing their neutralising/treatment capacity and often halting the neutralisation/treatment process.
In phosphate-bearing waters, thin but impermeable precipitates of compounds such as calcium phosphate (i.e. hydroxy-apatite) may form rapidly around particles of some treatment reagents such as calcium oxide. These processes inhibit complete dissolution of the calcium oxide, thereby retarding its capacity to fully treat the water.
Existing water treatment methods that encounter problems associated with deleterious precipitates remain inefficient, and consequently much more calcium-based or other treatment agents, are utilised in treatment situations than is theoretically required.
In addition to the formation of deleterious precipitates, some treatment reagents are subject to additional handling difficulties which are the result of their chemical properties. Calcium oxide, as a prime example, is commonly used in a range of water treatment applications due to its effectiveness, relatively low cost and relatively high theoretical solubility in most types of water. These desirable characteristics are offset by the handling difficulties encountered when this material is added to water in an attempt to form a calcium hydroxide solution/suspension. The hydration of calcium oxide to calcium hydroxide is a highly exothermic process, and in some circumstances may be rapid and progress to completion. However, when calcium oxide is added to a volume of water well in excess of its requirement to fully hydrate, as is generally the case with calcium oxide treatment plan
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Hochberg D. Peter
Hruskoci Peter A.
Kusner Mark
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