Natural Resources Research Institute Technical Report

Contributors: William M. Christensen, Dennis Fink, Steven A. Hauck, Mark J. Mueller, Julie A. Oreskovich, James A. Skurla, Thomas A. TothThe kaolinite-rich clays found in the St. Cloud area are currently used on a small-scale basis for ceramics by a local university. Testing of a specific clay bulk sample (MAQ) from Meridian Aggregates Company's granite quarry shows that these clays are heterogeneous and not suitable in a raw form for commercial use. However, selective mining and processing could provide a uniform commercial material. While inferior to the commercial kaolin to which it was compared, MAQ's properties can be enhanced by the addition of various controlling substances. Additives tested include ball clay, feldspar, and flint flour, all common to tile body formulation. Tests comparing Springfield C4 ball clay and Silver Bay anorthosite to commercial equivalents indicate desirable properties that would allow their substitution for existing additives in ceramic tile. The Springfield C4 ball clay increases plasticity and workability while reducing shrinkage and absorption, although it does increase the crossover point slightly. The crossover point (used as an indicator of maturity in a fired clay body) is the point on a graph where the shrinkage and absorption curves intersect. The Silver Bay anorthosite acts as a color lightener and retards shrinkage; however, absorption and crossover point can be increased significantly. When used in conjunction with ball clay, the crossover point is reduced. A flowchart showing the equipment necessary to produce ceramic tiles on a small-scale was developed, along with consideration for sufficient space and other supplies. Although the clay resources in the St. Cloud area are presently not developed, the establishment of a light industry ceramic tile processing operation is feasible.Funded by Minnesota Technology, Incorporated (Formerly the Greater Minnesota Corporation); Natural Resources Research Institute, University of Minnesota, Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811