Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-09-20
2002-02-26
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S683000, C210S747300, C210S906000, C210S911000, C210S912000, C210S913000, C210S688000, C405S128500, C405S129250, C502S065000, C502S073000, C502S081000, C502S084000
Reexamination Certificate
active
06350383
ABSTRACT:
The present invention relates to a sediment remediation process, together with a material for use in a sediment remediation process.
BACKGROUND OF THE INVENTION
The progressive eutrophication of estuarine and freshwater systems throughout Australia and overseas is often reflected in an increase in both phytoplankton bloom frequency and biomass, often with a shift to more nuisance species such as cyanobacteria. A significant proportion of the research into, and management of, estuarine and freshwater systems has focussed (with varying success) on reducing inputs of nutrients (in particular phosphorus) from the catchment.
However, the present invention has recognised that increased internal loadings derived from sedimentary nutrient stores accumulated over years to decades, constitute a major barrier to the effective management and restoration of estuarine and freshwater systems. Indeed, it is now apparent that if effective sediment-nutrient management strategies can be identified and adopted to modify internal nutrient (phosphorus) loadings, this will equip natural resource managers with a powerful tool for both short- and long-term estuarine and freshwater system management.
SUMMARY OF THE INVENTION
An aim of the present invention is to provide a sediment remediation process and a sediment remediation material which will assist in modifying, and in particular reducing, internal recycling sediment nutrient stores in estuarine and freshwater systems.
Broadly, the invention provides a method for remediating matter by removing oxyanion or phosphorus containing pollutants therefrom, the method comprising the step of contacting the matter with a substrate doped, cation-exchanged, or modified with, or otherwise having adsorbed complexing element(s) selected from Group IIIB and Group IVB elements.
The mechanism for reactions which occur in the substrate on addition of the complexing elements, and the chemical speciation of these elements are presently not well understood. By the term “modified” which term will be used hereafter, it is intended to cover whatever the reaction mechanism may be, which includes modification of the substrate by doping and/or cation exchange, and/or adsorption of the complexing element by the substrate. In addition, by the term “complexing element(s)”, ionic moieties containing such complexing elements are included, in addition to complexing element(s) alone.
Typical matter may comprise sediments in waterways and catchments, effluent from sewage treatment plants (commercial and/or domestic), industry, aquaculture (commercial and/or domestic and/or agricultural), sediments in water supply impoundments (lakes, reserviors), sediments in constructed wetlands and stormwater detention basins or similar engineered or natural impoundments.
Typical pollutants envisaged include phosphorus containing compounds, anions generally which are capable of forming complexes, and in particular oxyanions such as in particular phosphates, but also arsenate, vanadate, chromate and selenate, tungstate, niobate, tantalate, and tellurate, amongst others, and peroxyanions inter-alia such as persulphate. It is also expected that the method may have application in removing pollutants such as organic chemical contaminants such as pesticides or herbicides or trace elements, although this is not the primary objective of the invention.
Generally, phosphorus will be removed as dissolved phosphates or orthophosphate. Phosphates exist as different species, depending upon pH and other solution physico-chemical parameters. Phosphorus is often present in polluted aqueous environments in insoluble forms, and is transformed to soluble phosphate species by various processes that can occur within the environment. Examples of insoluble phosphorus include organically-bound phosphate which may become aqueously soluble due to biogeochemical processes, or phosphorus held in inorganic forms such as in mineral form as in mineral apatite or fertilizer, or that bound to crystalline and/or amorphous Fe-Mn-oxyhydroxide species all of which may be released due to various biogeochemical processes.
The method may include in addition, adding a water soluble salt of the complexing element selected from Group IIIB and Group IVB elements, along with the modified substrate. This would be expected to give rise to an immediate reduction in pollutant levels due to formation of complexes with the soluble salt, leaving the remediation material for more long term reduction in pollutants.
Preferably the salt is a chloride salt or a nitrate salt or a mixture of chloride and nitrate salts of the complexing element.
The present invention also provides a remediation material for use in reducing oxyanion or phosphorus pollutant loadings in matter, the remediation material comprising a substrate doped, cation-exchanged or modified with, or having adsorbed a complexing element(s) selected from the Group IIIB and Group IVB elements.
The substrate may be any suitable substrate having a moderate to high cation exchange capacity (CEC)—a substrate having a CEC of greater than about 30 milliequivalents per 100 grams (meq/100 g) having a ‘moderate’ CEC, while a ‘high’ CEC substrate may have a CEC of greater than about 100 meq/100 g and commonly about 150meq/100 g or greater.
It is preferred that the substrate is a mineral substrate due to these being in many instances relatively inert and/or harmonious in the environment.
In the most preferred form of the invention, the mineral substrate is an expandable clay such as saponite, bentonite or vermiculite. These materials are regarded as expandable clays due to their ability to absorb waters of hydration into their internal structure which may change the basal (d-) spacing.
Alternatively, the mineral substrate may be a fibrous, chain-like related clay mineral such as attapulgite, sepiolite, or palygorsite.
However, it will be appreciated that materials of a similar nature to clays, clay-like minerals, or expandable clays, may also be satisfactory. These may include materials both natural or synthetic. For instance, zeolites have also been investigated for use as the mineral substrate of the invention, both naturally occurring zeolites and artificially synthesised zeolites. Zeolites are also commonly a moderate to high cation exchange capacity material and although they are aluminosilicate minerals like clays, they have a different three dimensional framework structure with internal cavities.
The mineral substrate of the invention preferably has a high CEC in order to allow it to be modified to increase its pollutant or nutrient binding capacity, and in particular its phosphorous binding/absorbing/complexing capacity. Specifically, this involves the exchange of cations present in the mineral substrate with the nutrient complexing element or elements referred to above. This modification may be described as doping or cation exchange/ion exchange.
The mineral substrate may be pre-treated with a concentrated acid (e.g. HCl, H
2
SO
4
) to remove a large proportion of the interlayer and/or structural cations, before being treated with the complexing element. The pretreatment of clays with acid represents another pathway to prepare modified clays for phosphate adsorption. A potential advantage of this technique is that there may be a degree of modification to the underlying clay structure which enhances the uptake of the complexing element or other structural changes to the clay. These structural changes may make the clay more amenable to other modification steps which may improve the phosphate uptake capacity.
The complexing element is preferably an element capable of forming a complex with oxyanions. Most preferably the complexing element is capable of forming a complex with phosphorus containing compounds, as phosphorus is often the most common nutrient present in contaminated aquatic systems which may mean there is a high potential for algal bloom growth. Typically, the phosphorus will be present as phosphate anions in such aquatic systems.
The remediation material may be applied as a dry powder,
Commonwealth Scientific and Industrial Research Organisation
Hruskoci Peter A.
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