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<br /> <br />7 ~..• <br />:.:~ <br />[ <br />.... • u:•:~f~~~/~ :. <br />Saturoted Brine <br />Figure Z, Prog[ession of Caci[p Washed by MovabL Pipe TecMique. <br />x <br />A B <br />.I <br />'I <br />;~ <br />'.. •I <br />~;:~ ~f <br />~: GI <br />o l' - <br />., , <br />0 <br />X <br />b <br />Inert <br />Blanket <br />:. .'. <br />.~ <br />x <br />c <br />Figure 8. Forrna[ion of Spherical Shape by Revolu[ion of Concenr. is Quadrna;eu ls. <br />In order to facilitate multiple staging without the disadvantage of pipe movement, the circu- <br />lation system may consist of three or more concen[ric pipe strings as depicted in Fig. 9. When <br />circulation is being maintained through the upper strings, insoluble material is removed by peri- <br />odically switching the effluent to the tubing by means of a manifold at the circulation head. The <br />tubing should be of a size to assure sufficient velocity for particle removal. <br />Determining the Position and Size of the Blanket-Water Interface <br />In order for this type of controlled washing to be effective in producing cavities of close di- <br />mensions, the progress of the cavity must be monitored throughout the leaching process. This <br />can be done usually by establishing a relationship between the position of the blanket-water contact <br />and the volume of space occupied by the blanket material in order to determine the diameter and <br />position of the blanket-water contact. <br />303 <br /> <br />