Tuesday, November 17, 2015

Waterjetting 37e - Using Cavitation to disintegrate rock

In most mines the main objective is to recover as much of the valuable minerals contained within the host (or gangue rock) while minimizing cost. When miners have to go underground and haul the ore to the surface before the minerals are recovered then there is a considerable expense both in hauling all the rock, including the large otherwise valueless host rock, to the surface, and then crushing it to a small size so as to liberate and separate the valuable components.

The work at MS&T, for a number of years, has looked at ways in which rock can be disintegrated, as it is mined, so that the different components are separated as they are freed from the vein. While this work has progressed significantly since it started, this video (of poor quality for which I apologize, but it was what was available at the time) describes where we started the work.

Figure 1. Tom Fort explains the work on cavitation disintegration of rock

  The work was carried on in a number of ways after that, some of which has been described in an earlier post.

Perhaps most relevant to the video at the top of the piece, we were able to develop a more continuous mining process where the material would be mined from the solid in the mine, rather with small hand samples in the lab. While the technology could be easily developed from existing machines now used for hydro-demolition, a more telling picture is to show, by running the product from a test on a sample of dolomite hosting a vein of galena, where the product was run over a Wilfey table.

Figure 2. Mined sample run on a Wilfey table.

The result shows that clear fragmentation of the galena particles and their liberation so that they form a separate (silver) stream on the table from the darker dolomite particles that lie closer to the riffles. It is not quite as easy to see the larger particles of galena which were also separated, but would be more easily recovered perhaps with a screen, since they are not quite as easily streamed from the dolomite.

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Monday, November 16, 2015

Waterjetting 37d - Underground Drilling with Waterjets

The last post showed some of the experiments that we carried out as we developed a tool for drilling "around corners", demonstrating the ability of a high-pressure water jetting system to turn from a vertical well bore and drill out a lateral well within a turning radius of about 9 inches. This was not our earliest work on drilling, and that earlier effort had been directed to the reaming of geothermal wells.

The earlier project was also funded initially by Sandia Labs, although in this case the objective was slightly different. Overall we set out to show that one could go down a vertical well bore, some 9-inches in diameter, and ream a cavity 6-feet across down in the "hot dry rock" of a geothermal deposit.

When we began we weren't sure that we could drill in stressed rock, or what those effects on drilling rate would be. So we were fortunate to get some help from Doe Run and work in one of their mines, as the following video shows.

Figure 1. Early video on Underground Waterjet Drilling

  It was this series of tests that showed how relatively quiet water jets could be in drilling, unlike the competition at the time. Below the fold I will add the second part of this program, where we demonstrated the technique we planned on using for the reaming program.

Figure 2. Reaming a Geothermal Well Demonstration

Although this program moved on to focus on other aspects of the problem (we also demonstrated that this was practical in cutting granite, which led on to the Stonehenge and Millennium Arch projects) it was not until we were tasked with reaming large scale rocket motors, some years later, that we returned to this program, and developed the tools further.

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