Abstract: Disclosed is a method of pretreating sulphide ores or sulphide ore concentrates having high bismuth contents that have a disturbing influence on further processing of the ores or concentrates, such as to enable the ores or concentrates to be further processed for the recovery of their valuable metal contents or at least to facilitate such processing. The method is characterized by leaching the ore or the concentrate with sulfuric acid over a predetermined time period while supplying heat at a pH below 2, and thereafter separating from the leachate a leaching residue in the form of a product which is leaner in bismuth and more enriched with regard to its valuable metal content than the input material.

Abstract: The invention relates to a process for increasing the feed value of lignocellulosic materials by contacting the material with an alkaline liquid. The alkaline liquid supplied in excess is allowed to run off the material before any essential alkalization effect has been reached. After the liquid absorbed in the material has provided its effect an acid solution or nutritive solution is added to the material for neutralization of non-desired excess of alkali. Said solution is applied in such an amount as to at least correspond to the residual absorption capacity of the material resulting after the drainage due to the effect of alkaline liquid absorbed by the material. The invention also provides for an apparatus suitable for carrying out such process.