AN INVESTIGATION OF THE THERMALLY INDUCED WATER LIBERATION FROM ROCK SALT WITH POLYHALITE SEAMS UNDER IN-SITU CONDITIONS. - TEMPERATURE TEST 5 IN THE ASSE SALT MINE
The Temperature Test 5, which was begun in April 1982 to investigate the geological boundary conditions at heating of rock salt formations, was shut down according to schedule in February 1983 at termination of the 5th heating step. The test was carried out in the rock salt with polyhalite seams (Na2P) at the 775 m level of the Asse salt mine. Polyhalite (K-2Ca-2Mg(SO-4)-4 x 2 H-2O) contains crystalline water and may also be found in small quantities in the Older Halite (Na2beta), which is considered to be a suitable disposal medium. In order to investigate the temperature dependent start of the liberation of crystalline water, i.e., the decomposition of polyhalite in-situ, the rock salt was heated stepwise to 100 degrees C, 150 degrees C, 200 degrees C, 230 degrees C and 270 degrees C. The heaters were placed in a 7 m deep horizontal borehole. Apart from the initially high liberation rates in heating step 1, the highest liberation rates were registered in heating step 5 due to the original liberation of adsorptive water bound to the borehole wall. This was found to be a reference to the beginning of crystalline water liberation above 230 degrees C. In order to lay emphasis on these assumptions, extensive chemical - mineralogical analyses on heated rock salt were carried out in 1984. In order to obtain samples from the immediate surroundings of the heaters, the latter were uncovered by a special saw machine and thin sections were prepared from those samples. These thin sections showed partly decomposed polyhalite crystals 2 cm distant from the borehole wall (or heater surface). A detailed temperature analysis showed that such decomposed crystals were only found in salt samples taken from areas which had temperatures higher than 230 degrees C. Hereby it could be proved that the decomposition of polyhalite is negligible at 200 degrees C.
Bibliographic Reference: EUR 10392 DE (1986) MF, 93 P., BFR 150, BLOW-UP COPY BFR 475, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989125001700 / Last updated on: 1987-01-01
Available languages: de