A laboratory study of mineral deposition in a boiling environment

The precipitation of dissolved copper sulfate due to boiling in a porous layer has been studied. A compacted layer of glass beads is saturated with water in which the copper sulfate has been dissolved. The layer is heated from below and cooled from above until boiling occurs. The lower part of the layer is an isothermal, two-phase mixture of vapor and solution. Boiling occurs on the base plate and condensation on the upper boundary of the two-phase zone. Heat transfer is the result of the counter-percolation of the two-phases as in a heat pipe. The upper part of the layer is composed of the liquid solution; heat is transported through this layer by conduction and single-phase convection. No net loss of water vapor occurs. The concentration of the dissolved copper sulfate decreases exponentially with time due to the deposition of copper sulfate pentahydrate near the base plate and the deposition of partially hydrated copper sulfate throughout much of the two-phase zone. The rate of deposition is related to the rate at which boiling is occurring; a large fraction of the copper sulfate dissolved in the water that boils is deposited and does not redissolve. This mechanism of precipitation can be applied to mineralization due to the boiling of ground water adjacent to igneous intrusions. It is concluded that mineral deposits can be formed by this mechanism in a few thousand years.