Setting time and workability of magnesium phosphate ceramics slurry

In the nuclear industry, low and intermediate-level radioactive liquid wastes are often processed using methods that involve solidification. One of the most commonly used methods employs Ordinary Portland Cement (OPC) as a binder. While OPC is both versatile and inexpensive, there are alternatives that are used in certain instances where the use of OPC is not appropriate. As one of those alternatives, Magnesium Potassium Phosphate (MKP) Ceramics have found their niche applications in treating most difficult wastes such as salts, ashes, liquids, and sludge. A key characteristic of the formation of MKP is its setting time, defined as the length of time between mixing of the ingredients and solidification of the MKP, during which the slurry is capable of being poured into molds, where solidification is desired to take place. A method of direct, realtime measurement of the torque experienced by the slurry mixing system (hence the viscosity of the slurry) was developed to monitor the setting behavior (e.g., setting time) of the slurry, and to provide a means of predicting the workability limit of a slurry. The effects of pH, additives (such as boric acid) and the composition of surrogate waste on MKP setting behavior were also examined using the method. It was found that the addition of 1.5 wt% boric acid was capable of extending the setting time by as much as 20 times, relative to the case without any boric acid addition in the pH of range of approximately 2 to 5. (author)