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.

1 . 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 insoluble solids.  
     
     
         2 . A method as claimed in  claim 1  and wherein the solid containing material includes kaolin which is calcined by heating during the incineration of the insoluble solids.  
     
     
         3 . A method as claimed in  claim 1  and wherein the product of the incineration, optionally after one or more further treatments, is supplied for use as a pigment or filler in a paper making composition.  
     
     
         4 . A method as claimed in  claim 2  and wherein the product of the incineration, optionally after one or more further treatments, is supplied for use as a pigment or filler in a paper making composition.  
     
     
         5 . A method as claimed in  claim 1  and wherein the effluent or sludge is diluted with water prior to the treatment with acid and is dewatered or dried prior to the incineration.  
     
     
         6 . A method as claimed in  claim 1  and wherein the calcium present in the solid containing material is present as one or more compounds selected from calcium carbonate, calcium sulfate, calcium silicate and calcium phosphate.  
     
     
         7 . A method as in  claim 1  and wherein the acid treatment to cause dissolution includes adding a dilute acid selected from hydrochloric acid and sulfuric acid.  
     
     
         8 . A method as in  claim 1  and wherein sodium hydroxide is added to the solution separated by the separation step to form calcium hydroxide and then carbon dioxide is added to the calcium hydroxide formed to form a calcium carbonate precipitate.  
     
     
         9 . A method as in  claim 1  and wherein sodium carbonate is added to the solution separated by the separation step to form a calcium carbonate precipitate.