WP2: Mineral processing options for submarine massive sulphide ores

The main objective of WP2 was to assess the grade and recovery potential of SMS ore subjected to conventional and alternative processing and to reveal limitations of existing technology due to submarine aspects. The available samples from at Loki’s Castle consisted mainly of porous chimney fragments with metal grades and textures that can be assumed to be less favourable than those of the bulk of the deposit. As a result, conventional processing using froth flotation proved to be less successful than anticipated. Although a bulk sulphide concentrate could be produced, the complex mineralogy made it impossible to achieve selective separation of the different valuable sulphide minerals (e.g. chalcopyrite and isocubanite in the case of copper) or to separate these minerals from pyrite.  In addition to conventional flotation, both sensor-based sorting and hydrometallurgical leaching were investigated. The former technology could offer possibilities for pre-concentration on-site (surface or possibly even sea bed), whereas the latter could be a necessary alternative to physical separation when dealing with very fine grained ores with a complex texture. Experiments with sensor based sorting demonstrated that the use of X-ray transmission (XRT) made it possible to perform useful pre-concentration of the chimney material based on the density of the individual fragments. However, the applicability of sensor based sorting will depend heavily on the texture of the ore. The hydrometallurgical leaching experiments showed that valuable metals can be extracted efficiently with small residual losses (i.e. high recovery). Nitric acid produces the best results, but other alternatives are possible (hydrocloric acid or sulphuric acid). The process yields quartz, barite and elemental sulphur. Dissolution of SMS in the presence of sulphuric acid and Mn2+ was mainly due to galvanic interactions between primary marine minerals and manganese dioxide. Due to the reduced accessibility of freshwater in some countries and the high costs of hydrochloric acid, the mixed sulphate-chloride systems offer the possibility of economical leaching, particularly where seawater is easily available. So far, WP2 has resulted in three peer-reviewed papers, two conference papers and four posters/presentations.

images of product and waste samples (Kowalczuk et al 2018)