Patent ID: 7198805

Claim:
A method for producing humic acid salts by treatment of a water suspension of a plant raw material comprising the steps of: pre-mixing a 12–20% water suspension of plant raw material of lignin or lignosulphonate, a by-product of sulphite cellulose production, with an alkaline agent, which is sodium hydroxide; thereafter treating the suspension in a two stage high temperature treatment; wherein in a first stage of the two stage high temperature treatment the suspension is continuously heated with an oxidizing agent to a pre-oxidation temperature of 50–190° C. and a pressure of 0.5–3 MPa until a pH value of 10.5–12 is reached, and thereafter subjecting the mixture to a second of the two stage heat treatment at a temperature of 170–210° C. and a pressure of 0.5–3 MPa until a pH value of 8.5–10 is reached whereby a main oxidation takes place, thereafter cooling the mixture.