Bio-conversion of sulfide minerals

Bio-conversion of sulfide minerals

PhD research April 2006 – September 2009

Social impact


Sulfide minerals like pyrite are forming an important economical source for precious metals like gold, silver, and copper. The gold present is often called “invisible gold”, as it is present as sub-micron particles (Au0) and/or structurally bound gold (Au+1, Au+3). Even finely milled ore fractions can not be efficiently leached, because the gold is encased in the matrix of the minerals. Pre-treatment of the ore is therefore required to destroy or open up the mineral lattice structure. Nowadays oxidation techniques (chemical and biological) are applied to accomplish this aim. However, the application of oxidation techniques has some major disadvantages; a lot of energy is needed to provide the reactors with enough oxygen. Also, the main reaction product, diluted/polluted sulfuric acid, must be neutralized by lime and polluted gypsum must be stored.

The aim of this research is to develop a more environmental friendly and cost effective alternative by applying various biogeochemical redox conditions. This envisioned process should save energy and have a lower environmental impact than the chemical or biological oxidation techniques.

Technological challenge
The technological challenges of this project are:
-          Finding bacteria that are able to modify sulfide minerals
-          Finding optimal biogeochemical redox conditions
-          Determining/clarifying reactions that are taking place
-          A complete bio-conversion process design for sulfide minerals.


Name:           Ir. Alex Hol
Supervisors: Dr. R.D. van der Weijden

                   Dr. ir. P.N.L. Lens

Promotor:    Prof. dr. ir. C.J.N. Buisman

Graduated:   HLO (specialization Biotechnology),

                   HR&O, (Hogeschool Rotterdam)

                    Process Biotechnology, Wageningen University

Hobby’s:       Searching/collecting fossils and minerals, Fitness and Swimming.

Tel:              0317-482909
Financial support: Barrick Gold Corporation