Treatment of solid containing material derived from effluent

Abstract

A method of treating solid containing material derived from effluent or sludge from a plant for de-inking paper, the material containing calcium in the form of one or more insoluble calcium compounds, the method including the steps of treating the material with an acid to cause dissolution of the calcium thereby forming a calcium ion-containing solution in which insoluble solids are suspended, separating the solution from the insoluble solids and incinerating the separated solids. The solution containing calcium ions may be treated by adding one or more reagents to form a calcium compound precipitate, eg calcium carbonate. The particulate solids produced following the incineration step and following the precipitate formation may be employed as pigments or fillers in paper making or paper coating.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to the treatment of solid containing material derived from effluent, especially to recover useful materials therefrom.[0003] In particular, this invention is concerned with a method for recovering useful materials from what has hitherto been regarded as the waste material produced by an industrial plant for treating paper, especially for de-inking waste paper.[0004] Paper and paperboard products are generally made by preparing a dilute aqueous suspension containing cellulosic fibres derived from wood or from some other suitable fibrous material, and de-watering the suspension on a moving wire mesh belt to form a sheet material. The suspension may also contain a proportion of a mineral filler material which improves the brightness and opacity of the finished paper or board. Natural cellulosic fibrous materials are generally expensive, and the trees or other plants from which they are obtained must be replaced if the...

AI Technical Summary

Benefits of technology

[0028] If the solution in which the insoluble calcium precipitate is produced contains dissolved species these may optionally be recovered and re-used. For example, where the dissolved species comprises sodium chloride solution this may be electrolysed in a known way to produce sodium hydroxide plus hydrogen and chlorine gases. The gases may be recombined to produce hydrogen chloride from which hydrochloric acid can be recovered which can be re-cycled for re-use in the acid dissolution step. The sodium hydroxide can be recycled for re-use as the alkali metal hydroxide for addition to the calcium ion-containing solution. In addition, carbon dioxide is produced in the dissolution step this may be re-cycled for re-use in the precipitation step. In this way, the need to purchase chemical reagents and to dispose of by-products can be minimised or avoided.

[0029] The method according to the present invention beneficially allows minimization of the amount of solid waste from a de-inking plant thereby reducing or eliminating the cost and environmental impact of disposal of such waste. Furthermore, the method allows one or more useful products to be recovered in a manner which is simpler and cheaper than the relevant prior art.

[0030] The useful product recovered includes a calcined kaolin-containing particulate material which does not suffer substantially from the abrasiveness normally caused by incinerating kaolin and calcium carbonate together. In this case, the calcined kaolin composition may be used in various pigment employing applications, eg paper making as described earlier or in paper coating, filling of polymers, paints and the like. Such a product may show improved optical properties, eg brightness, compared with products produced by incineration of solids from de-inking sludge by prior published methods without discoloration from ink coloring materials, eg carbon, and in a cheaper manner.

[0032] Other particulate materials, eg silicate and aluminosilicate material contained in the de-inking reject may, as described hereinbefore, be converted after calcination into useful products, eg pozzolans, and the reagents used in the method according to the present invention may be recycled thereby minimizing reagent costs and waste disposal.

Problems solved by technology

Where the sludge solids treated include calcium carbonate this can react with kaolin present to produce a glassy composite phase which causes the particulate product to be abrasive.

As described in EP798268-A1, the incineration temperature may be controlled so as to minimise formation of the glassy phase, but this procedure can be relatively complicated and expensive to operate and may cause the resulting particulate product to have inferior optical properties, eg a reduced brightness.

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