Abstract: The invention relates to a process for preparing a usable product, in particular a water treatment solution which contains ferric iron, from an impure ferric sulfate solution which contains as an impurity at least one other metal, the process comprising a first precipitation step in which a base is added to the said impure ferric sulfate solution in order to raise the pH to approx. 2-5, preferably approx. 3-4, whereupon ferric hydroxide precipitates; following the first precipitation step, a second precipitation step in which there are added to the solution an oxidant and a base to raise the pH to approx. 6-10, preferably approx. 8-9, whereupon the said impurity metal precipitates; and one or more separation steps to separate from the sulfate solution the solids precipitated in the first and the second precipitation steps; as well as possibly an additional step in which the said separated solids, or a portion thereof, are treated further in order to form a usable product.

Abstract: A method for treating sludge from wastewater purification is described. In the method, a sludge is treated, which contains phosphorus and at least one metal which originates from precipitation chemicals and which is selected among divalent iron and aluminum, the pH of the sludge being adjusted to below 4, preferably below 2, for dissolving the content of the phosphorus and said metal in the sludge; the remaining sludge is separated; the solution relieved of sludge and containing phosphorus and said metal is treated for precipitation of the phosphorus content of the solution as FePO4 at a pH of 2-3; and precipitated FePO4 is separated. The method is characterized in that the solution which remains after separation of FePO4 and which contains said metal from the precipitation chemicals, is recycled to the wastewater purification. The phosphorus content of the solution is precipitated as FePO4 by adding an at least equivalent amount of Fe3−.

Abstract: A method for recovering at least one metal from an acidified waste water sludge by liquid-liquid extraction by providing an acidified waste water sludge containing ions of at least one metal and organic material, treating the waste water with an oxidizer to convert the organic material into a form that does not have an unfavorable effect on a subsequent liquid-liquid extraction, and subjecting the treated, acidified waste water sludge to a liquid-liquid extraction thereby obtaining an organic phase loaded with ions of said at least one metal, and subsequently recovering ions of said at least one metal from said organic phase.

Abstract: The invention relates to a method for the treatment of an impure aluminium oxide so that the organic impurities present therein it are converted into an insoluble and easily separable substance. According to the invention, aluminium oxide which contains organic matter as impurities is finely ground, the finely ground aluminium oxide is dissolved at an elevated temperature in sulphuric acid which has a concentration of at minimum 90% by weight, the amount of the sulphuric acid being at least stoichiometric in relation to the amount of aluminium oxide, the organic matter being carbonized into an insoluble and easily separable substance, and, if desired, the obtained mixture is treated further in order to form a solution-form or solid chemical which contains aluminium.

Abstract: The invention relates to a method for treating waste water sludge comprising at least one metal originating from a waste water treatment coagulant, and phosphorus and heavy metals in order to recover said at least one metal and phosphorus and to discharge said heavy metals. In this method said waste water sludge is acidified to dissolve metals contained in the sludge thereby yielding an acidified sludge solution containing at least 1% by weight of at least one metal to be recovered. In a first precipitation stage the pH of said acidified sludge solution is raised to precipitate at least one metal to be recovered as a phosphate, and thereafter the phosphate precipitate is separated, thereby leaving a solution comprising heavy metals. In a second precipitation stage the pH of said solution comprising heavy metals is raised and, if necessary, an appropriate chemical is added to precipitate heavy metals, and thereafter the precipitate is discharged.

Abstract: Waste water sludge which contains phosphorous, heavy metals and at least one metal originating from a waste water treatment coagulant, is treated in order to recover the phosphorous and the at least one metal, and to discharge the heavy metals. The at least one metal includes iron.

Abstract: A method for the treatment of sludge obtained from such a water treatment process wherein an aluminium or iron chemical is used as a coagulant, so as to reduce the amount of sludge, which method comprises the steps of:a) treating the water treatment sludge with an inorganic acid to produce an acidic sludge comprising dissolved aluminium or iron,b) optionally separating insoluble material from the acidic sludge to produce an acidic solution comprising dissolved aluminium or iron,c) treating said acidic sludge or said acidic solution with a +1-cation compound in the presence of sulphate ions in such conditions that the pH of the sludge or solution remains at a level where aluminium precipitates as an alunite compound or iron precipitates as a jarosite compound, andd) separating the precipitated alunite or jarosite compound from the remaining sludge.

Abstract: A method for preparing anhydrous ferric chloride from a hydrous solution containing ferric chloride that contains organic substances and/or ferrous chloride. In the method, water is removed from a ferric-chloride water solution or a solution, in which at least a portion of the ferrous chloride has been converted by oxidation into ferric chloride, by drying in an atmosphere containing hydrochloric acid. The anhydrous ferric chloride is refined by sublimating it into gas phase in a chlorine-containing atmosphere and by subliming it into a pure crystalline ferric chloride.