Abstract: The present invention relates to a method and as apparatus for simultaneous removal of thiosalts and nitrogen compounds in waste water, wherein the amount of thiosalts in the waste water is larger than the stoichiometric demand for the autotrophic nitrogen removal. The apparatus comprises a bioreactor (1) including an autotrophic bacteria culture carrying out a denitrification process using the thiosalts as electron donors, having an inlet (3) for receiving the waste water, and an outlet (4) for discharging the purified water. The apparatus comprises an oxygen supply device (6) arranged to supply oxygen to the water in the reactor and a control unit (10) arranged to control the content of dissolved oxygen in the reactor such that the excess of thiosalts is oxidized by the oxygen at the same time as the denitrification process is maintained.

Abstract: A method of leaching sulphidic material that contains metals and arsenic under oxidising conditions and with the aid of microorganisms is characterised by mixing the material with an acid aqueous solution to form a pulp, and in that the material is leached in a first leaching stage at a pH of below 2 and at a temperature that ranges from room temperature to about 55° C. in the presence of an active quantity of microorganisms of the mesophilic and/or moderately thermophilic type, wherewith the major part of the arsenic content of the material and possibly also part of its metal content is/are leached-out and the arsenic leached from said material is oxidised successively to a pentavalent state.

Abstract: A method of increasing the leaching yield of gold in the cyanide treatment of refractory ores or concentrates of such ores, while delivering air in an alkaline environment at atmospheric pressure, wherein gold present in said ores or concentrates is bound as tellurides. The method is characterised by carrying out the cyanide treatment at a temperature above room temperature, up to a temperature immediately beneath the boiling point of the leaching liquid. The treatment is suitably carried out at a temperature of 60-80° C., and at a pH between 10 and 12.

Abstract: A method of purifying an acid leaching solution obtained by processing hydrometallurgically material that contains valuable metals and also Fe3+ and Fe2+, and possibly also arsenic in solution. The major part of the Fe3+-content and the arsenic is precipitated out in a first stage, by adding pH-elevating agent to the leaching solution. The precipitate formed in the first precipitation stage is extracted from the solution and removed from the process. The solution is oxidised in a second precipitation stage while adding a further pH-elevating agent for oxidation of Fe2+ and precipitation of resultant Fe3+ and any arsenic still present. The resultant precipitate and any residual solid pH-elevating agent are then extracted from the solution and returned in the process to more acid conditions, and the thus purified solution is then processed to win its valuable metal content in a manner per se. The pH is suitably raised during the first stage to a value in the range of 2.2-2.

Abstract: A method for winning the valuable metal content of a leaching solution acidified with sulphuric acid, by solvent extraction and electrowinning and a following final product winning stage, for instance an electrowinning stage, wherein the pH of the leaching solution is raised successively to precipitate out the iron and arsenic present in a first precipitation stage, removing said first precipitate, and precipitating the valuable metal content of the leaching solution substantially totally in a following precipitation stage. The resultant precipitate containing valuable metal and gypsum is removed and leached in an acid environment to re-dissolve the valuable metal content, and the thus formed acid solution and its metal content are delivered to a solvent extraction circuit in which the metal content is converted to a substantial degree to an acid electrolyte from which metal or some other end product is won.

Abstract: A method for the total precipitation of valuable metals, such as copper, nickel, zinc, cobalt, etc., from a leaching solution that has been acidified with sulphuric acid and that is substantially free from impurities, by neutralizing the solution with lime and/or limestone. Neutralization is effected in at least two stages, wherewith only partial precipitation is effected in the first stage, and wherewith full precipitation of remaining valuable metal content is effected in the last stage, by adding a surplus of neutralization agent. Slurry containing precipitates and remaining solid neutralization agent formed in the last stage in the neutralization process is returned to the first neutralization stage, possibly after re-dissolving the slurry in the incoming acid leaching solution. The amount of slurry returned together with any further neutralizing agent added promotes the partial precipitation of the valuable metal content.