Magnetic Properties of Ceramic Minerals
Magnetic minerals and fine iron have plagued ceramic producers since the first glazed pot was produced many thousands of years ago. Early ceramicists adopted elaborate patterns to cover any imperfections caused by such contamination. But over time the demand for white or single colored ceramic products increased.
Ceramic producers turned to technology, with magnetic separators and screens, to identify and then remove problematic minerals and fine iron. Many ceramic raw material deposits, such as feldspar, silica sand, ball clay and kaolin, have problematic magnetic minerals including micas (muscovite and biotite), hematite, chromite, and iron stained quartz. Additionally, free iron is often introduced into the process from the wear or failure of the process plant.
Magnetic separation of minerals
Understanding the magnetic properties of the minerals in a particular ceramic raw material is vital when optimizing magnetic separation. The wide range of magnetic separator designs use different strengths and types of magnetic field to produce a separation. Several designs of magnetic separator may feature in a single mineral processing operation.
The range of high-intensity magnetic separators is divided into dry and wet processing. Many ceramic raw materials are handled and processed in a dry state. Most ceramic mineral processors magnetically treat their own reserves, as higher specification materials generate increased revenue. High-intensity magnetic separators remove magnetic minerals and free iron. Designs include the rare earth roll magnetic separator and rare earth drum magnet, which both utilize permanent magnets, or the electromagnetic induced roll magnetic separator.
Within the manufacturing plant, the spray dry ceramic process commonly introduces free fine iron into the process. Both the rare earth roll magnetic separators and drum magnets are employed to remove such problematic contamination.
Once the ceramic raw materials have been milled and mixed into slips, body and glazes, further magnetic extraction takes place. The milling process often liberates entrapped mineral iron, whilst free iron is reintroduced from the process. Electromagnetic filters, producing high magnetic fields, cleanse both the body and the glaze.
As a final check - and to prevent any visible contamination on the glaze - neodymium rare earth tube magnets or magnetic liquid traps with neodymium magnets are positioned as close to or within the glazing station. This captures any magnetic particles introduced to the glaze during transportation to the station.