Boliden Mineral Ab

Jan-Eric Sundkvist

B&ouml;rje Lindstr&ouml;m

&angst;ke Sandstr&ouml;m

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&deg; 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. The remaining leachable metal content of the material is leached-out in a following leaching stage in the presence of an active quantity of an extremely thermophilic micro-organism and at a temperature within the active range of said micro-organism, said temperature being higher than the temperature in the first stage. The pH is suitably raised in the second stage to a level at which the pentavalent arsenic present in solution is caused to transform to a solid state and precipitate-out as a metal-containing arsenate which is separate from the leaching solution together with unleached material in the pulp after termination of the leaching process.

Two-stage bioleaching of sulphidic material containing arsenic

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&deg; C., and at a pH between 10 and 12.

Recovery of gold from refractory ores and concentrates of such ores

A method of purifying an acid leaching solution obtained by processing hydrometallurgically material that contains valuable metals and also Fe and Fe , and possibly also arsenic in solution. The major part of the Fe -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 Fe and precipitation of resultant Fe 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 2.2-2.8, and in the second stage to a value in the range of 3.0-4.5. The oxidising process in the second stage is suitably effected by injecting air into the solution and by preferably using lime or limestone as the pH-elevating agent. Solid material extracted from the second stage is returned beneficially to the first stage. Some of the solid material taken from each precipitation stage can be recycled within respective stages as a nucleating agent.

Method of purifying acid leaching solution by precipitation and oxidation

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. The acid solution deplete of valuable metal and deriving from the solvent extraction stage can be returned to the stage in which the valuable metal content is re-dissolved and, when electrowinning is used for winning the end product, electrolyte deplete of valuable metal can be cycled from the electrowinning stage to the solvent extraction circuit.

Method for recovering the valuable metal content of a sulphuric acid leaching solution

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. Metal hydroxide/gypsum precipitate, free from neutralizing agent and formed in the first stage, is washed and then removed from the process for winning metal therefrom.

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Skellefteå, Sweden

Jan-Eric Sundkvist