NOVELTY - Recovering phosphorus compounds from sewage sludge ash, phosphorus products or phosphorus-containing wastes, comprises: carrying out acid decomposition of the phosphorus-containing compounds with a dilute mineral acid to obtain a filter cake and separating the filter cake from a filtrate; adding a sacrificial metal to the sewage sludge ash and dilute mineral acid, or to the filtrate after separating the filter cake, to reduce heavy metal cations; adding aluminum salt, mixtures of different aluminum salts or an aqueous solutions of the aluminum-salts; and increasing the pH value using a base.    USE - The method is useful for obtaining phosphorus compounds as secondary raw material for fertilizer production, during thermal phosphorus production (all claimed).    ADVANTAGE - The method is carried out in an economical and simple manner, is efficient with respect to environment, does not require heating sources or the reaction heat for heating, and makes use of reduced amount of neutralizing chemicals (base) required for precipitating the phosphorus product, thus it reduces the acid consumption.    DETAILED DESCRIPTION - Recovering phosphorus compounds from sewage sludge ash, phosphorus products or phosphorus-containing wastes, comprises (a) carrying out acid decomposition of the phosphorus-containing compounds contained in the sewage sludge ash, phosphorus products or phosphorus-containing wastes with a dilute mineral acid in a digestion tank to obtain a filter cake and separating the filter cake from the filtrate by filtration, where the filtrate has a pH of 0-1, (b) adding a sacrificial metal including aluminum, iron, and/or zinc (i) to the sewage sludge ash and dilute mineral acid, during or immediately after acid decomposition in the digestion tank, or (ii) to the filtrate after separating the filter cake into a separate container in order to reduce the formation of heavy metal cations, where the resulting metallic heavy metal is separated by filtration with the filter cake, or separately, (c) adding an aluminum salt, mixtures of different aluminum salts or an aqueous solutions of the aluminum-salts in a stoichiometric excess relative to the concentration of phosphorus, and (d) increasing the pH value in a range of 2.1-3 using a base for precipitating and separating the phosphorus compounds.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic flow diagram for recovering phosphorus compounds from sewage sludge ash, phosphorus products or phosphorus-containing wastes, the drawing includes non English language text.