Abstract:
The hydrostatic pressure differential existing in a column of fluent material conveyed through an excavated passage possessing a downward entrance run and upward return run facilitates hydrometallugical processing including metals recovery and treatment of ores. Conveyance of the fluent material through the passage is facilitated by appropriate means including a difference in elevation between the inlet and outlet and/or gaseous expansion applied proximate the bottom of the return run. Cooling of effluent proximate the outlet may be utilized consequent to application of heat during processing as in roasting ore. The passage is excavated through rock filly capable of containing the pressures anticipated and has an interior casing which seals the rock porosity. Iron reinforced concrete is recommended in appropriate wall thicknesses. Location of appropriate pipe lines for pressurized fluid additives including compressed gas and liquid chemical reagents and the location of electrical lines if utilized within this interior casing is also recommended. Continuous operation autoclaving of hydrometallurgical processes in a safe and economical manner is facilitated.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to hydrometallugical processing, more specifically to hydrometallurgical processing under pressure, and most specifically to hydrometallugical processing under hydrostatic pressure.  
           [0003]    2. General Discussion of the Prior Art  
           [0004]    It is well known that elevated pressures and temperatures facilitate various hydrometallugical processes. It is considered that conventional autoclaves are also well known which are characterized by construction above ground in a manner capable of maintaining elevated pressures and temperatures inside a chamber which requires a structure which resists the tensile force exerted by this pressure outward against ambient pressure upon the exterior of the structure.  
           [0005]    The housing of an autoclave localizes high pressure and temperature in a limited volume which must be isolated from the immediate environment for safety to personnel. Autoclave housings are typically manufactured from very durable, expensive, alloys based on stainless steel and titanium. Pursuit of metallurgical processing resistance to both extremely aggressive chemical reagents and extremely abrasive materials in processing would require utilization of special alloys inclusive of chromium, nickel, and molybdenum which can reliably withstand the combined action of high pressure and temperature, mechanical abrasion, and chemical aggression. No known steel or titanium alloys are reliably resistant to some highly effective chemical reagents such as chloride. Sealing the various lines involved for using a conventional autoclave system for hydrometallurgical processing is considered problematic with regard to safety and operational costs. All of the connections of all the lines from the pumps and compressors and to the chamber(s) along with associated valves, gauges, et cetera, must be sealed and the seals renewed periodically because these seals will wear quickly. These factors are considered to render conventional known autoclaves generally unsuited to many hydrometallurgical processes wherein continuous processing of a slurry is desirable.  
           [0006]    It is considered that a conventional autoclave possesses a chamber which is charged, locked, pressurized, processed, depressurized, and discharged. Operation in an economically continuous manner would require, with conventional technology, an extremely sophisticated system for the pressurization of the fluent material with simultaneous introduction of material at ambient pressure and temperature and removal of material at ambient pressure and temperature. In practical terms staging is required in which pressurization, processing, and depressurization are conducted in sequence either in a single chamber or in several chambers through which the material is conveyed through pressure locks which can withstand elevated pressures and temperatures and which system would necessarily require alternate cycling of elevated and ambient pressures and temperatures within a structure which is strong enough to resist the force of the interior pressure against the ambient pressure upon the structure exterior. Agitation of slurry is also desirable and this imposes another complication as does the typical necessity of cooling the effluent in addition to depressurization.  
           [0007]    The use of conventional autoclave technology for hydrometallurgical processing is consequently considered problematic and inherently constrained in a manner which effectively prohibits continuous, economic operation in addition to requiring a physical structure of such strength and complexity as to render the same impractically expensive.  
           [0008]    Statement of Need  
           [0009]    Because autoclaving of fluent material during hydrometallurgical processes requires staging in order to achieve pressurization, processing, and depressurization a truly continuous system is considered problematic and the attempt to provide a facsimile of continuous operation consequently expensive with regard to the equipment required, maintenance, and operation. A poignant need is therefore discerned for continuous autoclaving in hydrometallurgical processing which avoids the expense of facilitating pressurization cycles in a closed chamber and which avoids the expense of external structure which resists the force of the elevated interior pressure outward against the ambient pressure upon the exterior of the structure.  
         SUMMARY OF THE INVENTION  
         [0010]    Objects of the Invention  
           [0011]    The encompassing object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which is inherently less expensive than conventional systems.  
           [0012]    A primary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which is inherently less expensive in operation than conventional systems.  
           [0013]    A first auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which avoids alternate pressurization cycling of a chamber.  
           [0014]    A first ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which facilitates continuous operation.  
           [0015]    A second ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which facilitates continuous operation and is simple with regard to required equipment.  
           [0016]    Another primary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which is inherently less expensive in installation expense than conventional systems.  
           [0017]    A second auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which obviates the expense for a structure capable of safely withstanding pressures elevated from ambient.  
           [0018]    A third auxiliary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which obviates the expense for a structure capable of safely withstanding temperatures elevated from ambient.  
           [0019]    A third ancillary object of the present invention is the provision of a system for autoclaving during hydrometallurgical processes which minimizes the expense of the ancillary equipment required, particularly equipment required for conveying slurry and facilitating pressurization cycles.  
           [0020]    Principles Relating to the Present Invention  
           [0021]    In achievement of the above stated objects it is suggested that a continuous operation autoclave for hydrometallurgical processing which furthermore obviates the expense of the structure required as well as the expense of operation may be obtained with an excavated passage possessing a downward entrance run and an upward return run. The runs may be vertical or inclined and may have various processing stations appropriately located therealong but an excavated passage facilitates the elevated pressures desired for autoclaving. The passage contains an inlet and an outlet and an elevational difference between the two may be utilized to convey fluid or fluent material, particularly slurry introduced through the inlet through the passage and out the outlet or to assist in conveyance which is otherwise assisted.  
           [0022]    The use of compressed gas, especially air in what is known in the field as an airlift, is specifically suggested whereby the gas is compressed to a pressure above the hydrostatic pressure at the depth concerned and expelled into the slurry somewhere along the return run, preferably at the bottom of a vertical run. The gas so released is buoyant and rises in the return run thereby reducing the density of the slurry therein and propelling the fluent material up the return run. Alternatively or additionally, pressure may be increased at the inlet of the passage with the use of a conventional pump. The use of a pump is preferably minimized because slurry of the type primarily addressed herein is often extremely abrasive and consequently quite offensive to the interior surfaces of a pump contacting the same. The minimization of the use of a pump for impelling flow of the slurry, moreover, allows processing of a relatively thick slurry without the expense associated with using multiple pumps. A compressor for air release toward the bottom of the return run capable of propelling slurry flow of a given rate is considered less expensive than utilizing another pump for this because the slurry is both abrasive and generally incompressible while air is both relatively unabrasive and quite compressible.  
           [0023]    It is also recommended that a hyposometricaly resultant elevational head with respect to the inlet and outlet be utilized to convey the slurry through the passage preferably in conjunction with the use of compressed air released proximate the bottom of the return run and/or the use of a pump at the inlet to create a pressure differential with respect to the outlet all of which constitute means of inducing flow of the slurry through the passage and hence the autoclave which is in contrast to the use of multiple pumps for a conventional, above ground, system. A system in accordance with the principles relating to the present invention is inherently facilitative of continuous flow induced by various means and is inherently benefited by the depth of the excavation which determines the pressure naturally achieved and maintained by hydrostatic pressure during autoclaving. This enables a considerable reduction in the cost of a structure capable of withstanding the force of the pressure differential between the elevated pressure required of autoclaving and ambient pressure by using surrounding rock as a part of the structure. Excavation also substantially reduces the cost of a structure capable of safely withstanding the temperatures required of processing as the surrounding rock effectively insulates the autoclave from human exposure to the same. Cooling of the effluent prior to exposure above ground, if desired, is readily achieved with a cold water heat exchanger located toward the top of the return run.  
           [0024]    This requires however, even in the case of excavating the passage through solid rock, that the interior surface created by excavation be sealed. Ferro-reinforced concrete is recommended for the construction of an interior casing to the passage. Depending upon the particular characteristics of the autoclaving processes desired various thicknesses ranging from one half to two feet are recommended for a concrete interior casing and a casing head of greater thickness is suggested in certain cases wherein elevated temperatures and/or pressures proximate the inlet or outlet are anticipated. It is further suggested that pipe lines for the compressed air and other compressed gases or liquids utilized in processing be run through this casing which must withstand the pressures anticipated in compression against the surrounding rock but which need not withstand these pressures in tension as in the case of a conventional autoclave structure above ground. Steel must be utilized throughout in a conventional structure while a system in accordance with the principles relating to the present invention may use relatively inexpensive materials including ferro-reinforced concrete for the casing and silica based ceramic for a lining sealing the interior surface of the casing in a preferred embodiment in accordance with said principles.  
           [0025]    In addition to achieving a continuous operation which is very economic the cost of the installation is hence also reduced considerably in comparison with conventional autoclaving as the cost of a ceramic lined concrete casing is considerably less than an equivalently sized steel structure and while the costs of excavation must be incurred the total cost for a system in accordance with the principles relating to the present invention is considered to be a fraction of the cost of a conventional autoclave for hydrometallurgical processes possessing an equivalent capacity. While compressors, pumps, and heating apparatus are desired for some of the hydrometallurgical processes encompassed the simplicity of the basic system obviates the need for all the equipment required for cyclic pressurization of an autoclave chamber as well as the vast majority of the equipment associated with conveyance of slurry and agitation of the same during processing.  
           [0026]    And all of the structure and equipment required to create and maintain pressure in a conventional autoclave is considerably reduced by appropriate utilization of the hydrostatic pressure available in a fluidic column of sufficient depth. The apparatus otherwise required to develop and maintain this pressure as well as the apparatus required to facilitate cyclic pressurization of a chamber in autoclaving is wholly obviated. The equipment required for continuous operation is considerably diminished and simplified and large rates of processing thereby facilitated with an inherently simple, reliable, and safe system. Other benefits and advantages to be derived from the practical application of the principles relating to the present invention in fulfillment of said principles may be appreciated with a reading of the detailed discussion below of the preferred embodiments, especially if made with reference to the drawings attached hereto briefly described immediately below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the processing of ores containing precious metals with cyanidation utilizing separate shafts for the entrance and return runs.  
         [0028]    [0028]FIG. 2 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the processing of sulphide concentrates and ores with high sulphide content utilizing separate shafts for the entrance and return runs.  
         [0029]    [0029]FIG. 3 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention suited to the recovery of metals using hydrogenation in processing and utilizing a single shaft for adjacent entrance and return runs.  
         [0030]    [0030]FIG. 4 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention utilizing a single shaft for concentric entrance and return runs.  
         [0031]    [0031]FIG. 5 is a vertical plane cross sectional schematic view of a system in accordance with the principles relating to the present invention utilizing a several shafts for one entrance and two return runs.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]    FIGS.  1 - 5  depict a preferred embodiment of the principles relating to the present invention wherein a fluidic material inclusive of: a wet slurry  10 , a wet slurry  10  resultant from condensation of a gaseous slurry  50 , and a liquid solution  60 ; is conveyed in continuous flow through an excavated passage including an autoclave area  13  between at least one inlet  11  and at least one outlet  21  which comprise, respectively, openings of the passage at the top of an entrance run  12  and a return run  22  in communication with each other and which may be connected by an intermediary connecting run  32  all of which is sealed with respect to the surrounding rock  33  by a continuous internal casing  19 . The autoclave area  13  is determined by the presence of elevated pressure including hydrostatic pressure obtaining at a given depth of the fluidic column thereabove. The hydrostatic pressure possesses a linear relation to depth and is also a simple product of density which two factors, absent any additional pressurization, determine pressure elevation above ambient, and whereby the bottom of the excavated passage has the maximum pressure.  
         [0033]    A difference in elevation hypsometricaly between the inlet  11  and the outlet  21  may be utilized to convey fluidic material including a wet slurry  10  or liquid solution  60  simply poured at ambient pressure into the inlet  11  down the entrance run  12  and up through the return run  22  out the outlet  21  if the elevation of the inlet  11  is of sufficient elevation above the outlet  21 . Alternatively or in addition to this hypsometricaly determined elevational head it is recommended, especially for a hydrometallurgical processing of a wet slurry  10 , that a compressed air release  25  in the return run  22  preferably near the bottom  23  of the same as depicted in FIGS. 1 &amp; 2 be utilized to propel flow of the wet slurry  10  upward through the return run  22  and out the outlet  21 . A pump  31  may also be utilized to convey the fluidic material through the passage, preferably located upon the inlet  11  as depicted in FIGS.  1 - 3 .  
         [0034]    It has been recommended that the casing  19  be constructed from ferro-reinforced concrete a of a substantial thickness and that gaseous addition  15  and liquid addition  16  of reagents utilized in the hydrometallurgical processing be supplied through addition lines  17  run through the casing  19  which is preferably poured into a suitable mold after disposition of these addition lines  17 . Compressors  30  and pumps  31  are of further obvious utility for supply of gaseous addition  15  and liquid addition  16  of chemical reagents through the addition lines  17  as the hydrostatic pressure at the level of addition must be exceeded and the resulting injection may further be directed downward in the entrance run  12  to impart motive energy in the desired flow direction and will result in agitation of the wet slurry  10 , gaseous slurry  50 , or liquid solution  60  regardless of the direction of the addition. The volume rates of gaseous and liquid addition  15 ,  16  or reagent are further preferably variable so that the same may be coordinated with the rate of flow through the excavated passage in optimization of the hydrometallurgical processing resulting in the desired effluent  20  at the outlet  21 .  
         [0035]    It is also preferred, regardless of the specific hydrometallurgical processing performed, that an embodiment of the principles relating to the present invention possess a lining  29  of the passage bonded to the casing  19  which is further preferably comprised of acid resistant ceramic, based on silica or synthetic materials. With the preferred ferro-reinforced concrete construction casing  19  an appropriate ceramic lining  29  is easily bonded thereto and, since both materials possess similar, linear, heat expansion coefficients, thermal deformation is avoided and fracturing between the lining  29  and casing  19  obviated. This is considered of great importance to useful operational life of a given system. A silica or synthetic based ceramic lining  29  is highly resistant to chemically aggressive environments including chloride, saturated HCl, NaOCl, Cl 2 , and FeCl 3 .  
         [0036]    It is also noted that, regardless of the intended use, both the entrance run  12  and the return run  22  must be inclined from horizontal, that a substantially vertical orientation is generally preferred, and that therefore the ground area required is minimized which, in combination with the inherent isolation against elevated pressures and temperatures provided by excavation downward into rock  33 , enables a reduction of ground area required for a processing plant in accordance with the principles relating to the present invention in comparison with conventional technology of equivalent capacity by over ninety per cent.  
         [0037]    With regard to more particular hydrometallurgical processes several examples are discussed below with direct reference to FIGS.  1 - 3  respectively.  
       EXAMPLE 1  
     Hydrometallurgical Processing of Gold Bearing Ores by Cyanidation  
       [0038]    With reference to FIG. 1 an excavated passage possessing an entrance run  12  which is approximately twice the width of the return run  22  but approximately equivalent breadth, or dimension into the drawing sheet, is considered. A maximum depth at the bottom  23  of the excavated passage of approximately one hundred meters is suggested. With an arbitrary breadth of one meter and widths of two and one meters respectively for the entrance and return runs  12 ,  22  the total volume of the passage is three hundred cubic meters with the return run  22  possessing half the volume of the entrance run  12 . With a wet slurry density of 1.5 tons per cubic meter the hydrostatic pressure varies across the depths of twenty to one hundred meters from two to ten atmospheres or approximately thirty to one hundred fifty psig. A compressed air release  25  is provided at the bottom  23  of the passage which is also the bottom of a substantially vertical return run  22  supplied through an air line  27  which is preferably supplied by a compressor  30 . An associated accumulator and valving are not shown but are simply presumed in conventional utilization.  
         [0039]    Gold bearing ore, preferably in an aqueous wet slurry  10 , is fed through a pipe  61  through the casing head  69  at the top of the entrance run  12 . This introduction of wet slurry  10  through this inlet  11  is preferably pressurized and use of a pump  31  as depicted in FIG. 1 is suggested. Gaseous addition  15  from a pressurized supply of oxygen  35  is made as depicted along with liquid addition  16  from a pressurized supply of reagents  36  including cyanide solution. And gaseous addition  15  of compressed air is also made in the entrance run  12  as depicted beginning at about ten meters depth down to about twenty-five or thirty meters depth at five meter intervals while the gaseous additions  15  and liquid additions  16  of oxygen and cyanide solution, respectively, are made in eight to ten meter intervals from about thirty-five meters of depth down to ninety to ninety-five meters of depth. The addition lines  17  for the cyanide solution especially require corrosion resistant construction.  
         [0040]    Active aeration of the aqueous wet slurry  10  bearing gold ore by the gaseous addition  15  in the upper portion of the entrance run  12  partially oxidizes the surfaces of minerals therein such a sulphides and carbonaceous materials which prevents reaction of the same with cyanide further downstream. Exhaust air  26  escapes to ambient through an exhaust pipe  62  through the casing head  69  located at the top of the entrance run  12 . The use of a relief valve, not shown, upon the exhaust pipe  62  is suggested to maintain a pressure differential between the top of the entrance run  12  and ambient. This exhaust air  26  is devoid of toxic components.  
         [0041]    The aerated wet slurry  10  bearing gold ore flows downward into the autoclave  13  area in the lower portion of the entrance run  12  where gaseous and liquid additions  15 ,  16  are made as discussed above and further preferably including active carbon in suspension and in stoichiometric proportions with the oxygen and cyanide appropriate to the hydrostatic pressure of the depth of the addition. Proportions are readily adjusted by pressure modification in accordance with monitoring conducted with measuring devices mounted within the casing  19  exposed to the wet slurry  10  flowing thereby induced largely by the airlift provided by the compressed air release  25  proximate the bottom  23  of the substantially vertical return run  22  and propelled upwards through the same out the outlet  21  after which the processed effluent  20  goes through a separator, not shown, wherein compressed air and active carbon are extracted and the resultant effluent  20  then neutralized in recovery of the gold.  
       EXAMPLE 2  
     Hydrometallurgical Processing of Sulphide Concentrates and Ores  
       [0042]    With reference to FIG. 2 entrance and return runs  12 ,  22  separated from each other by a few meters or more are considered. This is in contrast to Example 1 wherein the two runs  12 ,  22  are seen to be substantially adjacent if in separately excavated shafts, and in sharp contrast to the examples depicted in FIGS. 3 &amp; 4, wherein directly adjacent and concentric arrangements, respectively, occupy the same excavated shaft are depicted. And, in contrast to the rectangular cross sections of the passage described above in Example 1, it is suggested that a circular cross section be utilized possessing an area of one to two square meters.  
         [0043]    The entrance run  12 , moreover, is seen to be comprised of three different areas: a roast chamber  51  in an upper portion, a condensation area  53  therebelow and an autoclave  13  below both. The lower end of the entrance run  12  is joined to the lower end of the return run  22  by a connecting run  32  which is preferably inclined downward as seen and of a similar cross sectional area as the return run  22  which is 20-30% less than that utilized for the entrance run  12  with the exception of the constriction between the roast chamber  51  and the condensation area  53  and the inlet  11  which is preferably comprised of an inlet pipe  61  as depicted through which crushed and otherwise prepared ore material is supplied under pressure to the roast chamber  51 .  
         [0044]    The casing head  69  through which the inlet pipe  61  runs is preferably five to eight meters thick to provide proper isolation. Sulphide material in a dry slurry  59  is added under pressure and oxidized in the roast chamber  51  at a depth of twenty to thirty meters in which considerable heat is applied, preferably by burning natural gas with the addition of compressed oxygen as shown wherein gaseous addition  15  from a pressurized supply of oxygen  35  and a pressurized supply of natural gas  37  is made in appropriate proportions and quantity to maintain a temperature in the roast chamber  51  of approximately 450-550 degrees Celsius. The resulting gaseous slurry  50  containing SO 2  and SO 3  flows into a condensation chamber  53  wherein cold water addition  52  is made from a pressurized cold water supply  55  to form sulphuric acid and reduce the temperature to 200-250 degrees Celsius with a commensurate increase in density. Further cold water addition  52  converts the gaseous slurry  50  into a liquid wet slurry  10  which is the state flowing into the autoclave  13  where gaseous addition  15  from a pressurized supply of oxygen  35  is made and the hydrometallurgical processes completed with the sulphuric acid created from the gaseous SO 2  and SO 3  which conversion prevents escape of these toxic gases into the atmosphere. The maximum depth suggested is 150-200 meters.  
         [0045]    It is recommended, as seen in FIG. 2, that a conventional heat exchanger  56  be located in the return run  22  proximate the outlet  21  to reduce the temperature of the effluent  20  and that an open air exhaust  26  be located above the outlet  21 . The effluent  20  is cooled by water run through the heat exchanger  56  which is seen to have a cold water supply  55  and a hot water return  57  after which the effluent  20  flows out the outlet  21  for separation and recovery of the hydrometallurgically processed materials.  
       EXAMPLE 3  
     Hydrometallurgical Processing Utilizing Hydrogen In Metals Recovery From Solution  
       [0046]    With reference to FIG. 3 an excavated passage possessing a suggested maximum depth of 300-350 meters and a recommended cross sectional area of approximately four fifths to one meter squared is considered. The entrance run  12  is of moderately larger cross sectional area than the cross sectional area of the return run  22  and both may be rectangular with the two separated only by the casing  19  therebetween so that only a single shaft is excavated. The casing  19  possesses a silica based, acid resistant, thermo resistant, lining  29  as does a inlet pipe  61 , which preferably possesses a cross sectional area of between three and six tenths of a square meter, through which filtered metal bearing solution  60  including, as examples, CuSO 4  or NiSO 4 , are fed under pressure preferably provided by a high pressure pump  71 .  
         [0047]    Gaseous addition  15  from a pressurized supply of hydrogen  39  is made, as seen in FIG. 3, along virtually all of both entrance and return runs  12 ,  22 . This is preferably done, as seen, with an addition line  17  running down through the casing  19  between the two runs  12 ,  22 . In this example it is desired to maintain relatively high pressures throughout the system and pressure locks  70  are therefore located upon both the inlet  11  and outlet  21  at the top of the casing head  69  at the top of the two runs  12 ,  22 . The pressure lock  70  upon the inlet  11  may be provided by a check valve  72  permitting flow only in one direction downline of a high pressure pump  71  while a relief valve  66  which opens in accordance with increased pressure will regulate outflow of the effluent  20  to an expansion chamber and collector  73  which may further comprise a condenser and which separates gaseous exhaust  76  from the liquid effluent  20 . The metal recovered therefrom is in the form of a powder suspended in the effluent  20 . The pressure locks  70  ensure maintenance of a relatively high pressure throughout the system by permitting only high pressure fluid inflow through the inlet  11  and pressurized outflow through the outlet  22 .  
         [0048]    Pressure in the upper portion of the entrance run  12  is further elevated in consequence to heat added in the heating area  63  which is preferably performed, as seen in FIG. 3, with use of an electric heating element  65  which is supplied with electricity through electric lines  67 . The desired temperature here is approximately 170-200 degrees Celsius. A heat exchanger  56 , preferably of the cold water type discussed above and located at the upper portion of the return run  22  as depicted in FIG. 2, is also considered desirable. The pressurized, filtered, metal bearing solution  60  is first heated and then saturated with hydrogen which is supplied essentially throughout the processing to achieve stoichiometric proportion with the rate of hydrogen consumption in the ongoing reactions. This particular hydrometallurgical processing therefore utilizes most of the entrance run  12  and return run  22  as an autoclave area  13 . It is noted that the hydrogenation reactions promoted thereby essentially benefit from higher pressurization and both the relatively great depth and maintenance of relatively high pressure throughout the system are intended to provide an economic system which is highly efficient. 2500-3500 cubic meters per day is considered an optimal rate of hydrometallurgical processing in this example.  
         [0049]    The above three examples discussed relative to FIGS.  1 - 3  are each considered to be characterized by a particular type of hydrometallurgical processing which is considered to benefit from the application of elevated pressures and temperatures during the same and which illustrate in a practical context the advantages to be gained with fulfillment of the principles relating to the present invention. While each example is particularized with regard to the system embodying said principles the actual hydrometallurgical processes have not been defined beyond the system characteristics considered desirable for each type of processing each of which encompasses a range of more specific processes according to the type of metals being recovered, the ore available, the concentrations of sulphide and other relevant materials, et cetera.  
         [0050]    It is mentioned in this vein that the definition of a metal ore itself is considered dependent upon whether the metal(s) therein can be “commercially extracted”:  
         [0051]    ORE. A metal-bearing mineral from which a metal or metallic compound can be extracted commercially. Earths and rocks containing metals that cannot be extracted at a profit are not rated as ores. Ores are named according to their leading useful metals. The ores may be oxides, sulfides, halides, or oxygen salts. A few metals also occur native in veins in the minerals. Ores are usually crushed and separated and concentrated from the guague with which they are associated, and then shipped as concentrates based on a definite metal or metal oxide content. The metal content to make an ore commercial varies widely with the current price of the metal, and also with the content of other metals present in the ore. Normally, a sulfide copper ore should have 1.5% copper in the unconcentrated ore but, if gold or silver is present, an ore with much less copper is workable, or, if the deposit can be handled by high-production methods, a mineral of very low metal content can be utilized as ore. ( Materials Handbook,  13th Edition, Brady &amp; Clauser, McGRAW-HILL Inc., 1991, page 586).  
         [0052]    It is hence considered that the processing of ores, which is a primary intention of the principles relating to the present invention, is often complicated by the presence of multiple metals in varying concentrations and secondly that the number of metals present in a given ore which are economically recoverable may be increased, or a lower quality ore made viable, “if the deposit can be handled by high-production methods”. It is considered that this observation more precisely touches on the larger significance of the present invention: hydrometallurgical processing in a continuous, economic, manner using an excavated passage autoclave enables commercial processing of ores which otherwise would not be commercially viable. The use of hydrostatic pressure generated by depth in a fluidic column maintained by a casing  19  with an appropriate lining  29  in compression against the surrounding rock  33  provides for continuous flow autoclaving and elevated temperature processing in a manner which is inherently less expensive and safer than a structure built above ground.  
         [0053]    It is thus considered that the present invention is very widely applicable to ores and processes which have hitherto been considered commercially unviable and encompasses applications well beyond the few particular examples described herein which are intended to encompass all presently known hydrometallurgical processing with respect to metals recovery from ore.  
         [0054]    In each of the examples detailed above with relation to FIGS.  1 - 3  it has, for instance, been considered advantageous to utilize a pump  31 , with one example utilizing a high pressure pump  71 , at the inlet  11  for the introduction of a wet slurry  10 , dry slurry  59 , or solution  60 . Earlier it was stated that obviation of equipment including pumps, particularly if processing a slurry  10 ,  59 , was considered an advantage gained with an embodiment in accordance with the principles relating to the present invention. This is considered to be the case even if a pump  31  or even a high pressure pump  71  is utilized because the pressures in the autoclave area  13  are still increased by hydrostatic pressure and are elevated much higher than would be possible with the equivalent pump in a conventional system built above ground.  
         [0055]    While in the case of hydrometallurgical processing using hydrogen in metals recovery from solution  60  a high pressure pump  71  is recommended for obtaining elevated pressures throughout the system. A conventional pump  31  is utilized with slurry  10 ,  59  primarily as the most practical means available for providing a high rate of flow of material to be processed through the inlet  11 . In the example involving introduction of a dry slurry  59  particularly, the type of processing addressed requires pressurization at the inlet  11  because the roast chamber  51 , in which the first step in processing is conducted, by nature of its operation creates considerable pressure. Any embodiment in fulfillment of the principles relating to the present invention utilizes an excavated passage with an inlet  11  and an outlet  21  and while the difference in elevation between the two may be utilized to impel flow therethrough and compressed air release  25  toward the bottom of the return run  22  impels flow through the same, the application of pressure upon the inlet  11  to create a pressure differential between it and the outlet  21  still provides a very useful means for increasing the rate of flow through the autoclave area  13 .  
         [0056]    The embodiments depicted in FIGS. 4 &amp; 5 are not related to any particular hydrometallurgical process but are intended to further illustrate the principles relating to the present invention. The embodiments depicted in FIGS.  1 - 3  each utilized one entrance run  12  and one return run  22  essentially parallel and adjacent to each other. In one example the two runs  12 ,  22  are fairly close, in another deliberately separated, and in the third directly adjacent. In the first two examples two different shafts are required along with a connecting run  32  while in the last only a single shaft is utilized. In FIG. 4 this variation is extended into use of concentric entrance and return runs  12 ,  22 . A pump  31  is utilized to supply solution  60  under pressure to a centrally disposed entrance run  12  which is surrounded by a casing  19  which has a lining  29  on both sides with the return run  22  being concentrically external within a larger diameter casing  19 . The outlet  21  is located at a modest elevational decrease from the inlet  11  and is open to ambient pressure. The pressure differential between the inlet  11  and the outlet  21  created by the pump  31  is the primary motive force impelling flow through the system.  
         [0057]    In FIG. 5 the use of multiple return runs  22  is depicted which are further distinguished over the previous examples by possession of a relatively modest and inconsistent inclination upwards from horizontal in comparison with the substantially straight vertical disposition characterizing previous embodiments. It is also noticed that the only force impelling flow is hypsometical and that a naturally occurring geological formation is exploited to provide a considerable elevational difference between the inlet  11  and the outlets  21 . This embodiment is considered illustrative of possible retrofitting of existing mine shafts which are frequently connected and which, in following veins of quality ore, often radiate outward from the bottom  23  of a central, substantially vertical, excavated shaft which in this case provides the entrance run  12  while two connected shafts provide two connected return runs  22 . Liquid addition  16  is also gravity fed through an addition line  17  located at the inlet  11 . The autoclave area  13  is comprised mainly of the lower reaches of the return runs  22  but also includes the lower portion of the entrance run  21 .