Method for purifying phosphoric acid from a mixture, in particular a pulping slurry, containing or consisting of phosphoric acid, organic compounds and water, comprising or consisting of the following steps: i) providing a mixture containing or consisting of phosphoric acid, one or more substance(s) S having at least one secondary carbon atom attached to an alkoxy group, wherein the substance(s) S is/are selected from the group consisting of methyl-isopropyl ether, ethyl-isopropyl ether, propyl-isopropyl ether, di-isopropyl ether, sec-butyl-methyl ether, sec-butyl-ethyl ether, sec-butyl-propyl ether, sec-butyl-isopropyl ether, sec-butyl-butyl ether, bis(sec-butyl) ether, sec-butyl-tert.-butyl ether, 3-methoxy-pentane, 3-ethoxy pentane, 3-propoxy pentane, 3-(1-methyl-ethoxy)-pentane, 3-butoxy-pentane, 3-(2-methyl-propoxy)-pentane, 3-(1-methyl-propoxy)-pentane, 3-(1,1-methyl-ethoxy)-pentane, 3-pentoxy-pentane, 3-(1-methyl-butoxy)-pentane, 3-(2-methyl-butoxy)-pentane, 3-(3-methyl-butoxy)-pentane, 3-(1-ethyl-propxy)-pentane, 3-(2-ethyl-propxy)-pentane, 2-methoxy-pentane, 2-ethoxy pentane, 2-propoxy pentane, 2-(1-methyl-ethoxy)-pentane, 2-butoxy-pentane, 2-(2-methyl-propoxy)-pentane, 2-(1-methyl-propoxy)-pentane, 2-(1,1-methyl-ethoxy)-pentane, 2-pentoxy-pentane, 2-(1-methyl-butoxy)-pentane, 2-(2-methyl-butoxy)-pentane, 2-(3-methyl-butoxy)-pentane, 2-(1-ethyl-propxy)-pentane, 2-(2-ethyl-propxy)-pentane, 2-methoxy-3-methyl-butane, 2-ethoxy-3-methyl-butane, 2-propoxy-3-methyl-butane, 2-(1-methyl-ethoxy)-3-methylbutane, 2-butoxy-3-methyl-butane, 2-(2-methyl-propoxy)-3-methyl-butane, 2-(1-methyl-propoxy)-3-methyl-butane, 2-(1,1-methyl-ethoxy)-3-methyl-butane, 1-(3-methyl-butoxy)-pentane, 2-(1-methyl-butoxy)-3-methyl-butane, 2-(2-methyl-butoxy)-3-methyl-butane, 2-(3-methyl-butoxy)-3-methyl-butane, 2-(1-ethyl-propxy)-3-methyl-butane, 2-(2-ethyl-propxy)-3-methyl-butane, further organic compounds, wherein one or more of the further organic compounds is/are selected from the group consisting of polysaccharides, oligosaccharides and hydrolysation products thereof, and wherein one or more of the further organic compounds is/are selected from the group consisting of organic solvents and water, and adjusting the molar ratio of phosphoric acid to the total of one or more substance(s) S as defined above in the mixture to be in the range of from 1: 0.4 to 1: 10, preferably to be in the range of approximately 1: 0.6 to 1: 4, especially preferably to be approximately 1: 0.85 to 1:2, ii) heating the mixture to 25 °C or more until phase separation occurs, iii) removing the light phase, and iv) separating the phosphoric acid from the heavy phase. i) providing a mixture containing or consisting of phosphoric acid, one or more substance(s) S having at least one secondary carbon atom attached to an alkoxy group, wherein the substance(s) S is/are selected from the group consisting of methyl-isopropyl ether, ethyl-isopropyl ether, propyl-isopropyl ether, di-isopropyl ether, sec-butyl-methyl ether, sec-butyl-ethyl ether, sec-butyl-propyl ether, sec-butyl-isopropyl ether, sec-butyl-butyl ether, bis(sec-butyl) ether, sec-butyl-tert.-butyl ether, 3-methoxy-pentane, 3-ethoxy pentane, 3-propoxy pentane, 3-(1-methyl-ethoxy)-pentane, 3-butoxy-pentane, 3-(2-methyl-propoxy)-pentane, 3-(1-methyl-propoxy)-pentane, 3-(1,1-methyl-ethoxy)-pentane, 3-pentoxy-pentane, 3-(1-methyl-butoxy)-pentane, 3-(2-methyl-butoxy)-pentane, 3-(3-methyl-butoxy)-pentane, 3-(1-ethyl-propxy)-pentane, 3-(2-ethyl-propxy)-pentane, 2-methoxy-pentane, 2-ethoxy pentane, 2-propoxy pentane, 2-(1-methyl-ethoxy)-pentane, 2-butoxy-pentane, 2-(2-methyl-propoxy)-pentane, 2-(1-methyl-propoxy)-pentane, 2-(1,1-methyl-ethoxy)-pentane, 2-pentoxy-pentane, 2-(1-methyl-butoxy)-pentane, 2-(2-methyl-butoxy)-pentane, 2-(3-methyl-butoxy)-pentane, 2-(1-ethyl-propxy)-pentane, 2-(2-ethyl-propxy)-pentane, 2-methoxy-3-methyl-butane, 2-ethoxy-3-methyl-butane, 2-propoxy-3-methyl-butane, 2-(1-methyl-ethoxy)-3-methylbutane, 2-butoxy-3-methyl-butane, 2-(2-methyl-propoxy)-3-methyl-butane, 2-(1-methyl-propoxy)-3-methyl-butane, 2-(1,1-methyl-ethoxy)-3-methyl-butane, 1-(3-methyl-butoxy)-pentane, 2-(1-methyl-butoxy)-3-methyl-butane, 2-(2-methyl-butoxy)-3-methyl-butane, 2-(3-methyl-butoxy)-3-methyl-butane, 2-(1-ethyl-propxy)-3-methyl-butane, 2-(2-ethyl-propxy)-3-methyl-butane, further organic compounds, wherein one or more of the further organic compounds is/are selected from the group consisting of polysaccharides, oligosaccharides and hydrolysation products thereof, and wherein one or more of the further organic compounds is/are selected from the group consisting of organic solvents and water, and adjusting the molar ratio of phosphoric acid to the total of one or more substance(s) S as defined above in the mixture to be in the range of from 1: 0.4 to 1: 10, preferably to be in the range of approximately 1: 0.6 to 1: 4, especially preferably to be approximately 1: 0.85 to 1:2, ii) heating the mixture to 25 °C or more until phase separation occurs, iii) removing the light phase, and iv) separating the phosphoric acid from the heavy phase.