The dissolution of olivine in acid : a cost effective process for the elimination of waste acids

Abstract

The disadvantages of continuing industrialisation, such as environmental impacts and the decreasing resources of natural raw materials, have to be mitigated by the development of sustainable technologies. By studying geochemical processes and properties of natural materials, new sustainable processes can be designed. This field of study is known as Geochemical Engineering (Schuiling 1990, 1991 ). A typical example of Geochemical Engineering is the use of olivine for the neutralisation of industrial waste acids (Schuiling et al. 1986). Olivine, the fastest weathering silicate mineral, is available in large quantities and provides an excellent buffer for naturally produced acids. The use of olivine for the neutralization of industrial waste acids is therefore appealing. Compared to conventional methods for the neutralisation of waste acids, the use of olivine has the advantage that it produces valuable by-products, like precipitated silica and magnetic ferrites, while it generates no new waste streams (Schuiling et al. 1986). Since the olivine dissolution rate under natural conditions is too low for industrial application, the rate must be increased by raising the temperature or by using higher concentrations of acid or higher olivine surface areas. The properties of the first by-product, precipitated silica, depend strongly on the reaction conditions (Lieftink 1997). A wide range of precipitated silica qualities can be produced by varying temperature, grain size and quantity of olivine and acid concentration. The Olivine Process may, therefore, also be considered as an interesting alternative for current production processes of precipitated silica. The Olivine Proccess for the neutralization of waste acids was invented in 1985 at the University of Utrecht and patented (Duth Patent PCT NL 85/00026), the patent is currently owned by Geochem Research B.V. From 1986-1987 research on the improvement of the neutralization process and on applications of the neutralization products has been carried out, supported by a grant from the Dutch Ministry· of Housing and Environment (VROM). In 1993 research continued under a project financed by the E. C. Brite Euram programme titled "Olivine/Dunite for Industrial and Environmental Applications" (GR-OLIV BRE2-CT92- 0.344). Part of the research carried out for this project is presented in this thesis. The main purpose of the investigations was to collect sufficient data, necessary for the design of a pilot plant.