Project Status: CSRP component of the project complete. Further work continued through AMIRA.
Project Participants: CSIRO, Rio Tinto, Anglo Platinum, AMIRA
Project Leader: Warren Bruckard (CSIRO)
Smelters charge penalties for some minor elements in concentrates and these penalties reflect the adverse impact on the smelting process and the difficulty that the smelters have in treating the waste streams generated. As demand for metal grows and high grade, low impurity deposits are replaced by those with higher impurity levels, the impact of penalty elements is increasing. In some cases, smelter capacity is constrained by the ability to remove and dispose of the penalty elements.
The primary method for dealing with penalty elements in concentrates has been to blend concentrates to stay below the limits set for smelter feed. If a viable early removal option for penalty elements can be developed the economics of many ore bodies would improve and the environmental impacts reduced. Elements such as arsenic could be removed from metal concentrates at the concentrator, treated to recover valuables, stabilised, and stored in an environmentally safe way.
Treatment options for dealing with penalty elements in ores are primarily determined by their association with other elements and their distribution in the ore. Knowledge of the mineralogy and grain size are important considerations in assessing treatment options. If the penalty elements are widely dispersed in the mineral phases the treatment options are usually limited to separation and removal in streams produced during smelting. If, however, the penalty elements are concentrated in discrete phases, options exist for early removal by physical or chemical means. Arsenic occurs in many minerals in enough ores to make developing such a process worthwhile.
CSRP funded a project in 2007/08 to develop new flowsheets for dealing with minor and toxic elements in the processing of base metal sulphides – see "Early Removal and Safe Disposal of Arsenic and Other Minor Elements During Base Metal Processing" (2D8). In that project, a new flowsheet for dealing with arsenic-bearing base metal sulphides was developed and tested at small scale in the laboratory. Arsenic was removed at the flotation stage of beneficiation so that a "clean", low-penalty element concentrate could go forward to smelting. The penalty element rich co-concentrate would then be treated by selective roasting to partition the penalty elements into a low volume stream and to recover valuables in a separate stream. The unwanted material would be chemically and physically stabilised such that it could be safely and economically stored.
The work from project 2D8 was then carried forward into this follow-on project (2D9 / AMIRA P970). This new project was established to further demonstrate at bench scale the technical feasibility of the early removal of arsenic by selective flotation, particularly of arsenic-bearing copper ores provided by sponsors – Anglo American and Rio Tinto. This project officially commenced in late May 2009 and is scheduled to run for two years. In 2009/10 both sponsors provided ore samples for the study.
The potential difference of a mineral-solution interface, which is indicated by pulp potential, has been shown to be closely related to the floatabilities of sulphide minerals. An initial set of pulp potential tests on the Rio Tinto ore indicated that there may be only a limited opportunity to produce a separation. Further tests are required to confirm what level of separation may be possible. Further work is also required on the ore to investigate whether chemical or physical changes to the test conditions provide a better separation opportunity.
For the Anglo ore, copper recoveries for the preliminary benchmark floats are lower than expected and further work may be needed to increase this before the initial pulp potential tests. Quantitative mineralogical data results (QEMSCAN) suggest that grinding the rougher pulp concentrate may be sufficient to enable some separation of the arsenic-bearing sulfides. While the major copper mineral in both ore samples is chalcopyrite, there would appear to be enough difference in the sulfide mineralogy for the project to benefit from testing on both ores. This project is entering its second year and continues beyond the term of CSRP with the support of AMIRA.