The early in situ leaching (ISL) of uranium mines in Southern Kazakhstan had many technical problems which led to poor operational and environmental performance. These included mineral precipitation of gypsum (CaSO4) and calcite (CaCO3) plugging the aquifer, restricting groundwater flow and exacerbating excursions; complex reactions of chemicals with clays in the aquifer soils leading to permeability loss; excursions through old exploration boreholes; and excursions outside the mining zone. The restoration of uranium borehole from solid contaminants at many sites was not successful and companies lobbied regulators to relax cleanup standards, and some sites still had significant problems even meeting these standards .
The problems of natural (claying) and technological (chemical) colmatations of borehole filter is an actual scientific and technical task. The degree of colmatation defines the economic feasibility of deposit development and also the price of a final useful product.
The solid contaminates represents the polydisperse system which skeleton consists of large particles in space between them there are small capillary and subcapillary channels, which becomes low-permeable for reservoir fluids. Solid waste such as gypsum is usually dispersed of as low level waste, sometimes after compaction or immobilization into clay matrix filling voids in the structure .
The resistance contaminated solid materials to the destruction during development and operation of uranium well depends on their structurally-mechanical properties that is from degree of dispersion and the sizes forming particles, adhesive forces between them, and packing density.
The restoration of colmatated borehole can be achieved by means of cumulative sand perforation, hydraulic fracturing, swabbing or acidic treatment but they yield temporary result with certain negative consequences . So after their application the contaminated zone is only partially destructed and the at further operation the new zone of solid precipitation can be formed in more distance from a cleaned well area.
Besides the realization of additional perforation and acid processing introduces own technological pollution in a ore strata. For example, the solutions of hydrochloric acid cause strong corrosion of technological pipes, destruction of cement stone which products drop out in a deposit thus reducing permeability of ore strata.
Without stopping on advantages and lacks of modern technologies of borehole restoration operations at ISL of uranium which are widely described in the scientific and technical literature  in details, we will pass to consideration of an offered new way of realization of a damage control which consists in application the cavitation devices, particularly, hydrodynamic cavitation (HDC) method.
The HDC is a method with effective use in destroying of elements of hydrosystems and complex inorganic and organic chemicals, biorefraction materials, etc. Pulsation of pressure and speed alternation are results of the varying geometrical conditions in a cavitation area .
The HDC has a dual effect: local and total . The local one reflects in accumulating ability of a separate cavitational cavern to release built-up energy of condensed type and brings cavitational destruction. As regard to the total effect, it is summed effect of the separate cavitational cavern. It spreads over a bigger surface and may cause its destruction.
The HDC of a liquid provide its activation, changes its physical and chemical properties, and intensifies the chemical and technological processes in the aqueous media. For strengthening cavitational influences on a liquid the complex multifactorial influence on a processed liquid is necessary. For these purposes the hydrodynamic, electrodynamic, piezoelectric generators of cavitation uses [7,8].
At the moment of cavitation caverns collaps following effects are observed:
2. local throws of pressure to several honeycombs МPа;
3. local development of temperature to several honeycombs of degrees;
4. liquid luminescence (sonoluminescence);
5. change of physical properties in the form of changing of рН media.
The influence of cavitation on water and water solutions is brought the process of water molecules splitting in cavitational bubbles.
2 Results and discussion
Numerous researches of cavitation process allow to make the conclusion that the nature of primary activation of molecules in bubble is electric .
In the hydrodynamic cavitators performs hydrodynamic effect due to the developed turbulence of a pulsation of pressure and speed of a stream liquid, intensive cavitation, impact waves and secondary nonlinear acoustic effects. Hence, the resulted features of occurrence of the cavitational hydrodynamic phenomena, namely, creation of a continuous hydraulic impact wave with allocation of a significant amount of kinetic and heat energy as a result of collapsing cavitational bubbles can serve as the theoretical precondition of target to use of cavitational influences at carrying out of restoration contaminated borehole on all its length, including filter and a sediment bowl at the presence some special washing chemicals.
The cavitational stream was evaluated by means of the Ventury-type like tube. The development of cavitation is controlled by pressure of the liquid stream from the pump of the drilling machine. The general scheme of restoration of contaminated well is presented on Figure 1. The pressure wave runs downstream from the collapse center to considerable distance with little or no damping, while the pressure wave running upstream is damped by a new cavity.
Fig. 1. The principle scheme of cavitational restoration of colmatated borehole
The hydrodynamic action on the wall of a borehole allows obtaining a two phase media – a gas-liquid system where gas bubbles exist during very short time because they implode due to hydrostatic pressure. A high speed of discharge jets allows them to leave the device casing and reach the obstacle wall of borehole where the bubbles implode and produce required work – to disperse the solid contaminates, clean or eroding of surface of the well. The imploding bubbles allow easily extract colmatants from porous or fractured rock: water drops, clay or sand and gypsum particles. And circulation of liquid in the well transports them to the surface. The back micro wave impact produces micro cracks in the rock and thus opens new path and improves permeability of the productive rock in bottom hole zone. Known methods are not capable to provide decompression in liquid sufficient to boil it adiabatically. The proposed device is capable to produce breaks of continuity of the liquid due to high flowing speed and periodic full or partial interrupting of the flow. In this case the extremely powerful inertial forces inherent to the moving liquid can be realized and fluid flow continuity can be implemented despite high hydrostatic pressure.
Suspended matter is removed from the filter zone and reservoir via the second side stream loop that is designed to sweep the debris from the floor of the contaminated area into the collector on well top. The filter is automatically backwashed throw pump at times to remove solid matter, which is sent to waste.
The solution of surfactants was used to decrease the hydrostatic pressure at restoration operation of well and keeping in a suspended state of broken colmatant particles. It has been shown that the presence of surfactants in the washing solution promotes an intensification the process of cleaning both a filter zone and effective destruction of productive rock. Besides, the presence of surfactants in the washing solution promotes careful washing of borehole wall from strangers balling which also are taken out on a well mouth.
On Figure 2 one can see the samples of colmatantes taken out from the bottom of borehole at cavitational cleaning operation.
Fig. 2. The samples of colmatants taken out from uranium borehole under cavitational restoration
For chemical dissolution of solid deposits, such as gypsum, iron hydroxides and other in washing liquids also was entered a small amount of sulfaminic acid (1-5 wt.%).
The advantage of the used chemical reagents in combination with the cavitational treatment of colmatated wells is that they contain concentration at 5-12 times less in comparison with the traditional technologies and can partially or completely exclude using of aggressive and expensive mineral acids such as hydrochloric, sulfuric or nitric acids.
The proposed method for hydrodynamic action on the wall of a borehole comprising the cavitating devices are simple by their design. In combination with chemical additives this device provides a continuous regime of a circular action on the wall of a borehole.
1. Hambleton-Jones B.B., Toen P.D., Economic geology. 1978. V. 73. P. 1407.
2. Allen B.L., Soil Sci. Soc. Am. SSSA. Special Publ. 1985. No. 15. P. 197.
3. Shamov N.A., Ljagov E.G., Zinatullyna E. Ya., Aseeva E.G., Bubelov A.B., Oil&Gas business. 2006. V. 4. No. 1. P. 47.
4. Gasanov A.P., Restoring of killed well. Guide book. Moscow: Nedra, 1983. 128 p.
5. Gogate P., Adv. Environmental Research J. 2002. No. 6. P. 2.
6. Bodurova D., Angelov M., Sci. Conf. Manufacturing and Management in 21st Century. Ohrid, Rep. of Macedonia, Sept. 16-17, 2004.
7. Sato K., Saito Y., JSME International J. 2002. V. 45. No. 3. P. 638.
8. Lui K., Kanno S., Shaw K.C., Liu X.D., Toh C.K., SIMTech.technical reports. 2007. V. 8. No 2. P. 85.
9. Pat RF. N20559110. Cavitation energy. The method of energy receiving.