Commonwealth Scientific and Industrial Research Organisation

Grant Brian Douglas

A process for removing silica and reducing total hardness of a natural or waste water containing silica and scale-forming ions comprises adding (i) magnesium hydroxide or a precursor of magnesium hydroxide and (ii) a soluble aluminate compound or a precursor of aluminate to said water while maintaining the pH of said stream at pH>8 to produce a layered double hydroxide in situ, wherein the layered double hydroxide contains the scale-forming ions in a lattice of the layered double hydroxide and silica is incorporated in the lattice of the layered double hydroxide as an interlayer anion and/or bound by the layered double hydroxide via one or more binding modes, wherein the process further comprises a recycling and regeneration step and/or a hydroxide addition step.

Process for removing silica and reducing total hardness from water

A process for simultaneously removing silica and reducing total hardness of a natural or waste water containing silica and scale-forming ions is described. The process comprises adding (i) magnesium hydroxide or a precursor of magnesium hydroxide and (ii) a soluble aluminate compound or a precursor of aluminate to said water while maintaining the pH of said stream at pH>8 to produce a layered double hydroxide in situ, wherein the layered double hydroxide contains the scale-forming ions in a lattice of the layered double hydroxide and silica is incorporated in the lattice of the layered double hydroxide as an interlayer anion and/or bound by the layered double hydroxide via one or more binding modes.

In situ process for producing layered double hydroxide (LDH) and further recycling of the LDH

A process for selectively separating a metallic constituent from other metals and other materials accompanying the metallic constituent in a mixture is described. The process comprises the step of providing the mixture in an aqueous solution such that the metallic constituent forms a complex anion in the solution. One or more of the other metals forms a cation or a complex cation in the solution. Another step includes contacting the solution with one or more additives to form layered double hydroxide (LDH) material in situ such that the complex anion is intercalated within interlayers of the LDH material and wherein one or more of the other metals are incorporated into the LDH material's crystal structure or matrix. Another step involves the addition of an LDH to an aqueous solution. The process involves selectively recovering the metallic constituent from the interlayer of the LDH by subjecting the LDH to a recovery treatment step(s) and as required, methods to modify the LDH to facilitate metal separation and recovery or contaminant stabilisation.

Selective separation of elements or commodities of interest in aqueous streams

A groundwater remediation method for treating acidic or alkaline groundwater containing divalent and trivalent metal cations includes the step of injecting a slurry or suspension of solid alkaline material into the ground, the slurry or suspension being injected into one or more regions such that the groundwater contacts the solid alkaline material and the divalent and trivalent metal cations react to form a layered double hydroxide (LDH) material.

Remediation of groundwater

A process for treating a natural or wastewater containing dissolved Mg or dissolved Al comprising the steps of adding at least one Mg-containing compound or at least one Al-containing compound to the natural or wastewater to thereby form a layered double hydroxide (LDH) containing Mg and Al as predominant metal species in a lattice of the LDH. The LDH may comprise hydrotalcite. The AL-containing compound may be aluminate or aluminium hydroxide derived from the Bayer process or from an alumina refinery.

Treatment or remediation of natural or waste water

A material and method for removal of environmental oxyanions (and especially phosphates), the material comprising a substrate such as a clay modified with complexing elements selected from Group IIIB, Group IVB, and lanthanide elements (or a mixture of such elements). The resultant modified substrate can bind oxyanions and make them unavailable for utilisation in the environment; in the case of phosphates, by algae and the like. The method includes forming a capping of material at the sediment/water interface, applying the material in the form of pellets at the sediment/water interface, or injecting the pellets into the sediment.

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Parkerville, Australia

Grant Brian Douglas