Patent Publication Number: US-2007119277-A1

Title: Methods for processing crushed solids with a liquid within a vessel

Description:
BACKGROUND  
      Many applications are known wherein a liquid is reacted with a particulated or crushed solid (“solids”) to enhance one or the other of the liquid or the solids (or both) for commercial benefit. One common application is to react a liquid “lixiviant” with a solid to extract a soluble compound from the solid by way of percolating or washing the solid with the liquid. (Accordingly, a “lixiviant” is a liquid used for this purpose.) This process is commonly described as “leaching”, and is known to various fields of endeavor. Typical examples include extracting valuable metals from ores containing the metals by contacting the ores with a lixiviant. The extracted metals will then be in solution with the lixiviant, and can be later removed from the lixiviant by known chemical processes, such as chemical precipitation, to render a relatively pure form of the extracted metals, or a form that can be subsequently processed to render a relatively pure form of the extracted metals. One example is to wash ore containing gold with a lixiviant containing cyanide to remove the gold from the ore. Other examples include washing oil shales with a solvent to extract petroleum from the shales, and washing coal with a sulfur-extracting liquid to remove sulfur from the coal. Yet another example includes contacting contaminated soil with a liquid-borne biological agent (or agents) to thereby decontaminate the soil.  
      In all of these processes the volumes of solids to be treated are typically considerable—on the order of tens to thousands of metric tons per day. In the case of ore leaching (to remove valuable metals from ores containing the metals), the most common process is to pile the ore into a “heap” on a leach pad, and then to introduce a lixiviant onto the top of the heap. After the lixiviant has passed through the ore heap via gravity, the lixiviant is collected and processed to remove the extracted metals from the lixiviant. The spent ore is then discarded (as for example by moving it to a spent ore pile), and new unprocessed ore is then placed on the leach pad, and the process repeated. Such leach pads often occupy areas covering many acres, and in some cases square miles. Due to the nature of the lixiviants used, and the metals being extracted from the ores, leach pads are typically subject to significant environmental controls to reduce the possibility of potential contamination of soil surrounding the leach pad. Further, the ore leaching process via ore heaps and leach pads is a slow process. Common leach times (i.e., the time between when the ore heap is initially formed and the lixiviant added to the ore heap, and the time when the ore is considered “spent” and is removed from the leach pad) are on the order of months. A six month leach time is not uncommon.  
      Other prior leaching methods and apparatus include: (1) batch tank leaching, (2) agitated vat leaching, (3) counter-current tank leaching, (4) permanent pad heap leaching (described briefly above), (5) re-usable pad heap leaching, and (6) bio-heap leaching. A common description for each of these methods and apparatus is a “leach circuit”.  
      The specific shortcomings of the prior art are as follows.  
      For agitated vat leaching, the basic operational concept is to provide an elevated contact rate of lixiviant and other additives to the surfaces of the ore particles by (a) increasing the surfaces of the ore which can be accessed by the lixiviant by grinding the ore to a particle size that exposes the desired metal or mineral value, (b) vigorously agitating the ore and lixiviant so as to provide an elevated level of contact between unconsumed reaction agents, and (c) to readily remove reaction outputs so as to maintain in majority concentration the unconsumed reaction agents.  
      The shortcomings of such a process include: (1) significant capital and operational costs are associated with grinding the ore to a small particle size and vigorously agitating such a dense media as an ore slurry; (2) the processing time required for the desired recovery level—as short as 24 hours in the typical case—in conjunction with the size limitations for a vessel which will afford reasonably good economic access of the agitation mechanical to the ore slurry, necessitates a large number of containment vessels, which in turn necessitates a plant of commensurate size to contain and support the operation of the containment vessels, all of which requires significant capital and real estate to construct; (3) small particle sizes typically present challenges for disposal of spent ore since special impoundments are typically required to de-water and stabilize it as permanent fill; (4) because of the relatively high capital and operating costs of such a leach process, the method is not economical for very low grade ores or ores which require leach times in excess of 24 hours to achieve economic recovery; (5) batch processing contains an inherent limitation in that there is wasted economic time between batch operations; and (6) because of the complexity of such a mechanically intensive process, design and construction times for the plant are relatively long (as compared to heap leaching, for example).  
      Heap leaching is an alternative to vat leaching and attempts to address the limitations of vat leaching with respect to low grade ores and ores that require longer leach recovery times (e.g., using certain oxides and certain sulfides). The basic operational concept of heap leaching is to trade-off leach recovery time for leach circuit processing size or volume by (1) secondary or tertiary crushing of the ore instead of grinding to a fine grain size, (2) agglomerating the ore into relatively uniform ore spheres to increase permeability of lixiviant and increase contact effectiveness rather than agitating the ore, (3) stacking in broad, relatively shallow piles on an impermeable layer instead of batching in expensive vessels, (4) sprinkling lixiviant on the ore, letting it trickle down under the action of gravity alone through the ore, and collecting the pregnant solution from perforated pipes on the bottom of the heap rather than submerging the ore within a vat or tank, (5) blowing air into the heap (as in the case of bio-heap leaching), and (6) removing the ore continuously from the pad as in the case of re-usable pads to make heap leaching a more continuous rather than a batch process.  
      Although heap leaching extends leaching technology to lower grade and harder-to-leach ores that are not economically done with vat leaching because of the implied processing volume required, heap leaching is less effective in extracting metals and the like from the ores, primarily due to the absence of submersion of the ore in the lixiviant and agitation of the ore (as in agitated vat leaching). Of particular concern in the use of a trickle-type application of lixiviant to a stack or pile of ore on a leach pad is channeling of the lixiviant, leaving significant portions of the leach pile without sufficient lixiviant to extract the theoretical maximum recoverable metals using the heap.  
      Another inherent shortcoming of heap leach is the inability to control environmental inputs such as temperature and oxygenation of the heap, which are critical factors in bio-heap leaching where the effectiveness of the bacteria is closely dependent on these variables.  
      Perhaps the greatest shortcoming of heap leaching is the capital and operating costs associated with large volumes of material, especially in the case of re-usable pads. Whereas in vat leaching the ore is transported in a slurry in pipe conduits, heap leaching, because of the large geometric extents of leach pads and complexity of stacking a stable heap, has been performed almost exclusively with conventional overland conveyors and specialized spreading and reclaim conveyors, which imply high capital and operating costs as compared to the compact plant piping of vat leaching.  
      What is needed then is an economical, efficient method and/or apparatus to react solids and liquids with one another that achieves the benefits to be derived from similar prior art apparatus and methods, but which avoid the shortcomings and detriments individually associated therewith.  
     SUMMARY  
      One embodiment provides for a method of processing selected solids with a selected liquid, the method including the steps of providing a vessel, and crushing the solids to not less than a predetermined median particle size. The crushed solids define, or are referred to herein, as crushed solids. The method also includes the step of reacting the crushed solids with the liquid within the vessel, such that a pregnant leach solution and post-reaction solids are derived. At least some of the reacting of the aforementioned step occurs under conditions of a predetermined hydrostatic head. The method further includes the step of migrating the pregnant leach solution and the post-reaction solids through the vessel substantially under the influence of gravity alone. Furthermore, the method includes the step of extracting the pregnant leach solution and the post reaction solids from the vessel.  
      Another embodiment provides for a method of processing a mine ore with a lixiviant, the method including the step of providing a reaction vessel, wherein the vessel defines solids outlet openings and liquid outlet openings. The method also includes the step of crushing the mine ore to not greater than a predetermined size, such that crushed ore is defined or derived. The method further includes the steps of reacting the crushed ore with the lixiviant within the reaction vessel, thus deriving a pregnant leach solution and post-reaction solids, and extracting at least some of the pregnant leach solution from the reaction vessel via the liquid outlet openings substantially under the influence of gravity alone. The method includes extracting the post-reaction solids and at least some of the pregnant leach solution from the reaction vessel via the solids outlet openings substantially under the influence of gravity alone.  
      These and other aspects and embodiments will now be described in detail with reference to the accompanying drawings, wherein: 
    
    
     DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagrammatic view depicting a system that can be used to perform a method according to one embodiment of the invention.  
       FIG. 2  is block diagrammatic view depicting details of the system of  FIG. 1 .  
       FIG. 3A  is flowchart depicting a method according to one embodiment of the invention.  
       FIG. 3B  is a continuation of the flowchart of  FIG. 3A .  
       FIG. 3C  is a continuation of the flowchart of  FIG. 3A . 
    
    
     DETAILED DESCRIPTION  
      In representative embodiments, the present teachings provide methods and apparatus for processing solids such as run-of-mine ore, in a substantially continuous manner, so that one or more materials of interest can be extracted or isolated from the ore and further processed to a condition deliverable to the market place.  
      The following terms are defined as used herein:  
      Run-of-Mine Ore: Refers to matter comprising at least one material of interest that is to be extracted or separated from the balance of the matter. Run-of-mine ore (or, interchangeably, ore) is in essentially the same condition as when it was removed from its natural or native source and, typically (but not exclusively), defines a substantially solid, chunk-like consistency and includes individual particles of substantially varying size. Non-limiting examples of materials of interest within such ore include gold, silver, platinum group metals, gallium, lead, germanium, refractory metals, molybdenum, copper, zinc, uranium, cobalt, nickel, light metals, crude oil, caregens, rare earth elements, etc. Other ores, comprising other respective materials of interest, can also be used. Examples of a native source for run-of-mine ore include, but are not limited to, a shaft mine, an open pit mine, a strip mine, etc.  
      Lixiviant: This refers to any of a number of chemical compounds, typically (but not necessarily) in a liquid state, which chemically reacts with run-of-mine ore so as to dissolve, or “leach”, one or more materials out of the ore and into solution with the lixiviant. Non-limiting examples of lixiviant include an aqueous solution of acid or acids, an aqueous solution of acid or acids including an oxidizing agent, an aqueous solution of an alkali or alkali&#39;s, sulfuric acid, a solution including sulfuric acid, an aqueous solution of an alkali or alkalis&#39; including an oxidizing agent, an aqueous solution of cyanide including an oxidizing agent, an aqueous solution of sodium or calcium hypochlorite, an aqueous solution of ferrous or ferric sulfate, an aqueous solution of ferrous or ferric sulfate including an oxidizing agent, an aqueous solution including a bacterial catalyst, an aqueous solution of chlorine, an aqueous solution of hydrogen peroxide, a solution of ammonium thiosulfate, or an aqueous solution of air and sulfur dioxide and copper. Other suitable lixiviants can also be used. Various embodiments allow the use of a lixiviant (or lixiviants) of typically greater concentration than those used in known heap leaching operations. Furthermore, the concentration (and/or other characteristics) of a lixiviant can be controlled to tighter tolerances, if desired, during continuous mode operation of various embodiments, as compared to known heap leaching operations.  
      Pregnant Leach Solution (PLS): This refers to a liquid comprising a lixiviant—in some overall degree of chemical depletion or expenditure—and one or more materials dissolved into solution therewith. Thus, pregnant leach solution typically results from a chemical reaction between a solid material, such as crushed run-of-mine ore, and a pristine (new, fresh, or regenerated) lixiviant.  
      Post-Reaction Solids (PRS): This term refers to solids, typically in a crushed form, which have reacted with a lixiviant such that at least some amount of one or more materials are dissolved out of the solids. As used herein, post-reaction solids are usually defined by crushed run-of-mine ore that has reacted, to some degree, with a lixiviant as generally defined above. That is, such post-reaction solids are typically defined by crushed ore matter that has been depleted, to some extent, of one or more materials previously present in its original (pre-reaction) condition. In some cases, post-reaction solids (PRS) will include some quantity (i.e., trace or residual amounts, etc.) of pregnant leach solution (PLS) until and/or unless further treatments or processing steps are performed to remove (e.g., leach) such PLS borne by the PRS.  
      Barren Solution: Generally, this term refers to lixiviant that has been previously used within a leach process (i.e., was once a pregnant leach solution) and has been processed or otherwise sufficiently reconstituted (i.e., recycled) so as to be useful in one or more embodiments. Non-limiting examples of such recycling steps can include removal of the materials dissolved into solution with the PLS, reconstitution by gas injection or addition of new acid, etc. In one example, a barren solution is derived that can be used within a wash process in order to leach (soak, or free) another liquid out of a solid material, thus defining an aqueous leachate. In another example, a barren solution is defined by sufficiently recycling PLS so as to derive a lixiviant in substantially new condition, and which can be used as such.  
      Turning now to  FIG. 1 , a block diagrammatic view depicts a system  100  that can be used to perform one or more methods in accordance with the present teachings. While the system  100  depicts particular elements used in accordance with one embodiment, it is to be understood that other elements (not shown) can be used, and/or selected ones of those elements shown  FIG. 1  can be omitted, in accordance with other embodiments. Thus, the system  100  as depicted in  FIG. 1 , is but one of any number of systems that can be used in accordance with the present teachings.  
      The system  100  includes a supply of run-of-mine ore (ore)  102 . The supply of ore  102  is typically piled in a covered or uncovered fashion to wait further processing, as described hereinafter.  
      The system  100  includes a crusher  104 . The crusher  104  can be defined by any suitable means for crushing the ore  102  to a predetermined median (or, optionally, a mean, not-less-than, or not-to-exceed) size. In one embodiment, the crusher  104  is defined by a jaw mill. In other respective embodiments, the crusher  104  is defined by a gyratory type or SAG mill. One of ordinary skill in the mining engineering arts is aware of numerous such crushers  104  for suitably crushing run-of-mine ore  102 , in accordance with the specific type of ore  102  and/or the desired median crushed size, and further elaboration is not required for purposes herein. In any case, the crusher  104  is suitably selected and used to crush the run-of-mine ore  102 , thus deriving (i.e., defining) a supply (or stream) of crushed solids (i.e., crushed ore)  106 .  
      The system  100  includes a supply of lixiviant  108 . The lixiviant  108  can be defined by any suitable such lixiviant as defined above. The lixiviant  108  is reacted with the crushed solids  106  in order to derive one or more desired by-products (or effects) of the reaction such as, for example, a pregnant leach solution as defined above. For example, the lixiviant  108  can be suitably defined so as to react with the crushed solids  106  such that gold is leached out of the crushed solids  106  and into solution with the lixiviant  108 . Other suitable lixiviants (i.e., liquids, etc.)  108  can also be used in accordance with the particular type of crushed solids  106 , the desired reaction to occur therewith, etc. One of ordinary skill in the mining or chemical arts is aware of numerous such lixiviants  108  and their respective uses.  
      The system  100  of  FIG. 1  also includes a slurry preparation tank  107 . The slurry preparation tank (hereinafter, slurry prep tank)  107  can be defined by a tank or box-like structure and can (optionally) be lined with a hard coating or other suitable wear- or corrosion-resistant material. In one embodiment, the slurry prep tank  107  is formed of steel and is lined with ceramic tile. Other embodiments of the slurry prep tank  107 , respectively formed from other suitable materials, can also be defined and used. The slurry prep tank  107  is configured to receive respectively controlled flows of the crushed ore  106  and the lixiviant  108 . In another embodiment (not shown), the slurry prep tank is also configured to receive a flow of a suitable flocculant. The slurry prep tank  107  serves as a mixing chamber wherein the crushed ore  106  and lixiviant  108  (and flocculant, if used) are combined so as to define a wetted material (or slurry) stream  109 . In another embodiment of the system  100  (not shown), the slurry prep tank  107  is provided in conjunction with suitable piping or other material conduits so that flow of the crushed ore  106  can be optionally bypassed around the slurry prep tank  107 , while the flow of lixiviant  108  into the slurry prep tank is curtailed. In yet another embodiment of the system  100  (not shown), the slurry prep tank  107  itself is omitted altogether.  
      The system  100  of  FIG. 1  further includes a mass flow reactor  110 . The mass flow reactor (MFR)  110  is also referred to herein as a vessel. One or more embodiments of mass flow reactor  110  suitable for use in accordance with the present teachings is/are described in detail in U.S. patent application Ser. No. 10/447,801, titled METHODS AND APPARATUS FOR PROCESSING MIXTURES OF LIQUIDS AND SOLIDS, as filed with the United States Patent and Trademark Office on May 29, 2003 and as incorporated herein by reference in its entirety. The MFR  110  provides a vessel-like structure within which the crushed solids  106  are reacted with the lixiviant  108 . The crushed solids  106  and the lixiviant  108  can be received by the MFR  110  as respectively separate flows or as, or in combination with, the slurry stream  109 , in accordance with the desired mode of operation. As depicted in  FIG. 1 , it is presumed that reaction of the crushed solids  106  with the lixiviant  108  results in the derivation of post-reaction solids and pregnant leach solution, respectively. Other solids/liquids reactions, resulting in other solid and/or liquid by-products, can also be performed within the MFR  110 .  
      The mass flow reactor  110  of  FIG. 1  is configured to permit the post-reaction solids and the pregnant leach solution to migrate through the MFR  110  and to be extracted there from substantially under the influence of gravity alone as a stream of post-reaction solids  112  and a stream of pregnant leach solution  114 , respectively. In this way, the mass flow reactor  110  is distinct, for example, from an agitated vat or other type of ore-handling apparatus wherein driven paddles, augers and/or overall rotary motion are used (whether in conjunction with gravity or not) to forcibly induce ore (or other materials) to migrate from an entry point to an exit point. Further operational aspects of the mass flow reactor  110  will be discussed in detail hereinafter.  
      The system  100  of  FIG. 1  includes a heat exchanger  115 . The heat exchanger  115  receives the flow of PLS  114  from the mass flow reactor  110 . The heat exchanger  115  can be defined by any suitable form such as, for example, a plate-and-frame design, a serpentine tube design, a multi-tube single-pass design, etc. One of skill in the mechanical engineering arts is aware of numerous heat exchanger  115  designs and their general use and further elaboration is not needed for purpose here. In one example, the heat exchanger  115  recovers heat from the PLS  114  and routes it (interconnecting means not shown) for pre-heating the lixiviant  108  prior to introduction into the slurry prep tank  107  and/or the MFR  110 . In another example, such recovered heat is simply expelled to atmosphere via a suitably coupled cooling tower (not shown). In yet another example, heat recovered from the heat exchanger  115  is used to pre-heat water or another fluid for use in an electrical generation plant (not shown). In any of these examples, the pregnant leach solution  114  is cooled to define a cooled PLS stream  117 . In yet another example, the heat exchanger  115  is used to heat the PLS  114  to a temperature greater than that as it is received from MFR  110 , prior to subsequent processing of the (heated) PLS  114 . In such a case, the pregnant leach solution is heated to define a heated PLS stream  117 . In yet another embodiment of the system  100  (not shown), the heat exchanger  115  is optionally bypassed or otherwise inoperative, or the heat exchanger  115  itself is omitted altogether.  
      The system  100  includes pregnant leach solution process (PLS process)  116 . The PLS process  116  can be defined by any suitable process (or combination of sub-processes) configured to receive the pregnant leach solution stream  114  from the mass flow reactor  110 , the cooled/heated PLS stream  117  from the heat exchanger  115 , and/or the PLS stream  134  (described hereinafter) and to separate (i.e., extract) one or more materials out of the residual pregnant leach solution. For example, a suitable PLS process  116  can be defined and used that causes gold to precipitate out of solution with the remaining PLS liquid advancing to the next stage. Non-limiting examples of process steps performed by the pregnant leach solution process  116  include any suitable one, or combination of, heating or cooling, clarification, filtration, bulk precipitation, pH modulation, solvent extraction, electrowinning, mercuric retorting, smelting, carbon column absorption, magnetic separation, cyclonic separation, etc. One of ordinary skill in the mining engineering arts is aware of numerous, well-established methods and materials for extracting particular materials out of pregnant leach solution and specific definition and elaboration is not required.  
      In any case, the pregnant leach solution process  116  includes suitable process steps resulting in the extraction and isolation of one or more minerals, metals, and/or other materials  118  in a condition suitable for provision to the market, or further processing, if desired. Also, the PLS process  116  can be defined and operated so as to reconstitute (i.e., recycle) the lixiviant within the PLS stream  114 ,  117  and/or  134 , or some fraction thereof, so that a renewed lixiviant stream (or supply)  148  is derived. As depicted in  FIG. 1 , the renewed lixiviant  148  is routed back to and combined with the supply or source of lixiviant  108 . In another embodiment (not shown), the PLS process  116  is defined and operated so as to derive a stream (or supply) of barren solution (not shown). Other embodiments of the pregnant leach solution process  116  can also be defined and used.  
      The system  100  of  FIG. 1  also includes a screen process  120 . The screen process  120  can include any suitable mesh-like apparatus such as, for example, a mesh conveyer belt, a vibratory screen assembly, etc. Other suitable screen process  120  apparatus can also be used. The screen process (or screen)  120  is configured to receive and support the post-reaction solids  112  such that post-reaction solids  112  of less than a predetermined size are separated from the balance of the PRS stream  112 . In one embodiment, the screen process  120  is configured so that post-reaction solids of less than ⅝ inch, defining fine solids (or “fines”), are separated from the balance of the post-reaction solids  112 . Other configurations for separating other sizes of post-reaction solids  112  (i.e., solid matter) can also be defined and used. Thus, typical operation of the screen process  120  derives a stream (or supply) of relatively coarse post-reaction solids  122 , and a stream (or supply) of fine solids  124 .  
      As depicted in  FIG. 1 , the coarse solids  122  are routed onto other processing  126 , which can include any desirable step or combination of steps for handling the relatively coarse solids  122 . Such other processing  126  step or steps can include, for example, detoxification and/or disposal of the coarse post-reaction solids  122 , further extraction of another material of interest therefrom, processing and/or market preparation of “cleaned” coal or oil shale (e.g., coal or oil shale from which sulfur has been “washed” or leached within the MFR  110 ), etc. One of skill in the mining arts is aware of numerous subsequent steps that can be performed after screen separation of fines from coarse solids, and further elaboration is not needed for purposes herein.  
      The system  100  of  FIG. 1  further includes a centrifuge process  128 . The centrifuge process  128  includes any suitable apparatus configured to receive the fine post-reaction solids (fines)  124  and to additionally separate pregnant leach solution (i.e., PLS  114 ) there from by way of centrifugal force (i.e., rapid rotation within a drum), thus deriving a stream (or supply) of pregnant leach solution  130 . The pregnant leach solution  130  can be routed if needed to a clarifying process  132 , described in detail hereinafter. Also, the centrifuge process  128  derives a stream (or supply) of generally dried (i.e., “dewatered”) post-reaction solids  136 . One of ordinary skill in the mining arts is aware of various suitable centrifuge processes and apparatus, and further elaboration is not required.  
      The system  100  also includes a barren solution (or water) wash  140 . Typically, the barren solution wash  140  can be used to leach additional PLS (i.e., PLS  114 ) out of the (dried, or “dewatered”) fine solids  136 . For example, some fine solids  136  include surface geometry, absorption characteristics, or other considerations that economically justify use of the barren solution wash  140  in order to recover additional material of interest (i.e., cyanide complexed gold, etc.) therefrom. In one embodiment, the barren solution wash is provided by way of a vessel substantially mechanically equivalent to the mass flow reactor  110 . However defined and used, the barren solution (or water) wash  140  derives a stream (or supply) of aqueous leachate  142  borne by the (dried) fine solids as they exit the barren solution wash  140 . In a sense, the fine solids  136  have been “rewetted” by way of soaking (leaching) within the barren solution wash  140  in the interest of recovering additional material of interest therefrom (e.g., dissolved copper, etc.). In some cases, the barren solution or water wash  140  is not used at all.  
      The system  100  also includes another centrifuge  144 . The centrifuge  144  can be defined by any suitable apparatus configured to receive the stream of “rewetted” fine solids from the barren solution wash  140  and to separate the aqueous leachate  142  therefrom by way of centrifugal force. In this way, the centrifuge  144  derives a stream (or supply) of liquid aqueous leachate  146  and a stream (or supply) of re-dried (or “dewatered”) fine solids  145 . As also depicted in  FIG. 1 , re-dried fines solids  145  are optionally routed onto other processing  138 , which can include any desirable step or combination of steps for handling the re-dried fines solids  145 . Such other processing  138  step (or steps) can include, for example, detoxification and/or disposal of the re-dried fines  145 , further extraction of another material of interest therefrom, cyclonic (or other) separation of different sizes (or classes) of fines material  145 , etc. One of skill in the mining arts is aware of numerous subsequent steps that can be performed after centrifuge separation of liquid from fines, and further elaboration is not needed for purposes herein.  
      The system  100  includes a clarifying process  132 . The clarifying process  132  can be defined by, or include, any suitable apparatus or processing step (or steps), if any, as desired or required, to remove solids from or otherwise handle the stream of pregnant leach solution  130  generated by the centrifuge process  128 , and/or the aqueous leachate  146  generated by the centrifuge  144 . For example, in a case where the PLS  130  contains 5000 ppm solids, reacted lixiviant and material of interest therein (e.g., dissolved copper, etc.), the clarifying process  132  can be suitably defined to remove a substantial fraction of the solids therefrom. In any case, the clarifying process  132  derives a stream (or supply) of pregnant leach solution  134  to be routed on to the PLS process  116  described above. In another embodiment of the system  100  (not shown), the clarifying process  132  is bypassed or omitted altogether. In yet another embodiment (not shown), the clarify process  132  can be suitably interconnected to the heat exchanger  115  so as to be heated or cooled thereby.  
      The system  100  of  FIG. 1  depicts particular system elements (i.e., process apparatus) coupled in particular cooperative relationships. However, it is to be understood that other systems (not shown) can also be defined and used in accordance with various corresponding embodiments. Further exemplary operation of the system  100  will be described hereinafter. While the system  100  of  FIG. 1  is described above in terms of processing run-of-mine ore (i.e.,  102 ), it is to be understood that another system (not shown), including a mass flow reactor (e.g., MFR  110 , etc.), can also be defined and used for decontaminating soil and the like. One of ordinary skill in the mining or industrial arts and/or geological sciences will recognize that the MFR  110  can provide a basis for any number of substantially continuous processes involving reactions between solid and liquid materials.  
       FIG. 2  is a block diagrammatic view depicting selected details of the system  100  of  FIG. 1 . As depicted in  FIG. 2 , the mass flow reactor (i.e., vessel)  110  is coupled to receive the stream of crushed solids (i.e., crushed ore)  106  directly—that is, the slurry prep tank  107  of  FIG. 1  is not included. Furthermore, the mass flow reactor  110  is coupled in fluid communication with the supply of lixiviants  108 . As depicted in  FIG. 2 , the MFR  110  receives the crushed solids  106  via at least one point (or opening)  150  proximate an open top of the MFR  110 . However, in another embodiment (not shown), the MFR  110  is configured to receive the crushed solids  106  via at least one point (or opening) elevationally lower with respect to the MFR  110 . It is to be understood that the system  100  is suitably equipped to regulate the flow of crushed solids  106  into the mass flow reactor  110  over some predetermined range, including complete shut off (zero flow).  
      The mass flow reactor  110  is also configured to receive the lixiviant  108  at a plurality of liquid entry points (or openings)  152  elevationally distributed within the MFR  110 . While not specifically depicted in  FIG. 2 , it is understood that the mass flow reactor  110  is suitably equipped (e.g., via valves, pressure regulators, electronic and/or pneumatic controls, etc.) so as to throttle, or regulate, the flow of lixiviant  108  (i.e., liquid) through each of the liquid entry points  152  over some predetermined range, including complete shut off. The flow of lixiviant  108  can be independently controlled through each liquid entry point  152 , suitably ganged so as to throttle each liquid entry point  152  flow in unison with the others, etc.  
      The MFR  110  is also configured to permit the extraction of post-reaction solids  112  from one or more solids exit points (or openings)  154 . Typically, at least one such solids exit point  154  is coincident with, or substantially proximate to, a bottom center “B” as defined by the mass flow reactor  110 . Other respective suitable locations defined by the MFR  110  can also be used for locating the solids exits points  154 . In any event, the mass flow reactor  110  is suitably equipped so as to throttle the flow of post-reaction solids  112  through each of the solids exit points  154  over some predetermined range, including complete shut off. The flow of post-reaction solids  112  can be independently controlled through each solids exit point  154 , coupled (ganged) so as to throttle each exit point  156  flow in unison with the others, etc.  
      The MFR  110  is further configured to permit the extraction of pregnant leach solution  114  at a plurality of liquid exit points (or openings)  156  elevationally distributed within the MFR  110 . It is to be understood that the mass flow reactor  110  is also suitably equipped so as to throttle (regulate) the flow of lixiviant pregnant leach solution  114  (i.e., liquid) through each of the liquid exit points  156  over some predetermined range, including complete shut off. The flow of PLS  114  can be independently controlled though each liquid exit point  156 , ganged such that each liquid exit point  156  flow is throttled in unison with the others, etc.  
      It is important to note that the mass flow reactor  110  as depicted by  FIG. 2  is configured such that post-reaction solids  112  and pregnant leach solution  114  (as well as, to some respective extents, crushed solids  106  and lixiviant  108 ) are induced to migrate (or flow) thorough the MFR  110  substantially under the influence of gravity alone, in the prevailing direction indicated by the arrow “G”. It is to be further understood, of course, that post-reaction solids  112  and pregnant leach solution  114  also migrate toward their respective solids exit points  154  and liquid exit points  156 , in various directions which deviate from the prevailing direction “G” in order for material (e.g., PRS  112  and PLS  114 ) extraction from the MFR  110  to be performed. However, such extraction of the post-reaction solids  112  and the pregnant leach solution  114  is also performed substantially under the influence of gravity alone. As used herein, “substantially under the influence of gravity alone” refers to migration or motion of respective materials through the mass flow reactor  110  without the use of other mechanical driving means or influences—for example, the mass flow reactor  110  is devoid of any driven paddles or augers, downward and/or upward liquid jetting, or vibration, shaking, rocking or rotation of the MFR  110 , and wherein gravity accounts for not less than ninety percent of the overall migration-inducing force when the mass flow reactor  110  is operated with a gaseous pressure (other than ambient atmospheric) present over the liquid and/or solids materials being processed within the MFR  110  (e.g., see location “U” in  FIG. 2 ). This makes operation of the mass flow reactor  110  distinct from other types of vessels or processing conduits known in mining or the related arts.  
      The mass flow reactor  110  of  FIG. 2  is also configured so as to define an internal cavity of volume “V”, and a maximum possible (or working) depth “L” of liquid there in. In this way, it is possible to establish a predetermined hydrostatic head gradient by providing and/or maintaining the corresponding depth “L” of liquid (i.e., lixiviant  108  and PLS  114 ) within the MFR  110 . In one exemplary embodiment, the MFR  110  is configured such that a stratum corresponding to a hydrostatic head “H” in excess of  65  feet of the liquid is present, and can be maintained, within the mass flow reactor  110 . Other configurations of MFR  110  corresponding to other (potential) magnitudes of hydrostatic head can also be used. In any case, the mass flow reactor  110  can be suitably configured to provide a zone (or stratum) where at least some of the reaction of the crushed solids  106  with the lixiviant  108  can take place under a predetermined hydrostatic head “H” of the liquid. As depicted in  FIG. 2 , the MFR  110  can be generally open to ambient atmospheric pressure at an elevationally upper end “U”. In another embodiment (not shown), the MFR  110  is configured such that a non-atmospheric pressure (i.e., a relative vacuum or over-atmospheric pressure) is present over the liquid within the MFR  110 , wherein such pressure—be it atmospheric or not—can be provided by way of any suitably selected gas (e.g., air, O 2 , N 2 , NO x , CO 2 , etc.).  
      As depicted in  FIG. 2 , the mass flow reactor  110  is coupled in fluid communication with a supply of gas  158 . The MFR  110  receives the gas  158  by way of at least one gas entry point (or opening)  160 . Such gas entry point or points  160  can be selectively located and/or distributed within the MFR  110  as desired or required. Non-limiting examples of the gas  158  include an oxygen/air mixture, a sulfur dioxide/air mixture, air, pure oxygen, a gaseous oxidizing agent, or any of these or another suitable gas or gasses dissolved in a liquid or lixiviant that is injected into the reactor  110  via entry port(s)  160 , etc. Other suitable gases  158  can also be defined and used in. For example, the gas  158  can be an oxygen/air mixture of predetermined ratio that is provided to the MFR  110  for purpose of oxidizing sulfur compounds present within or liberated from the crushed solids  106  so that such oxidized sulfur compounds are more readily handled at some subsequent process (not shown) external to the mass flow reactor  110 . Furthermore, the mass flow reactor  110  in the upper end “U” (or area proximate thereto) can be suitably equipped with ducting or piping, fume collection hoods, fans, etc. (not shown), so that gases (e.g., the gas  158 , a gaseous by-product or by-products of reaction, etc.) can be captured/collected and routed away from the MFR  110  for containment, processing, etc. In any case, one of ordinary skill in the mining arts is aware of numerous processes in which one or more gases can be injected into a reaction zone for one or more purposes, and further elaboration is not required.  
      The mass flow reactor  110  of  FIG. 2  can also be coupled to a supply of flocculant  170  that can be controllably introduced into the MFR  110  at one or more flocculant entry points (or openings)  172 . The flocculant  170  can be defined by any suitable agent used to cause relatively fine particles of the crushed solids  106  to adhere to one another, thus defining a plurality of larger solids entities. In an alternative embodiment, the flocculant  170  is defined by any suitable agent that causes such fine particles of the crushed solids  106  to adhere to relatively larger particles (or chunks) of the crushed solids  106  (agglomeration). In this way, an overall permeability of the crushed solids  106  with respect to the lixiviant (liquid)  108  within the MFR  110  can be suitably affected so as to increase contact between the two. In any case, the flocculant  170  can be provided to the MFR  110  when such flocculation or agglomeration is desired. One of ordinary skill in the mining arts is familiar with the selection and use of flocculants  170  as applied to processing ore “fines”, and further elaboration is not required here.  
      In another embodiment (not shown), a supply of inert solids is provided and selectively used so as to affect and/or stabilize one or more physical characteristics during reaction of solids with liquid(s) within a mass flow reactor (e.g., the MFR  110 , etc.) such as, for example, increasing or decreasing heat conductivity, increasing or decreasing heat absorption, increasing or decreasing heat capacity, etc. Non-limiting examples of such inert solids (not shown) include steel spheres, etc.  
       FIG. 3A  is flowchart  200  depicting a method in accordance with one embodiment of the present teachings. The method of the flowchart  200  is described hereinafter in reference to system  100  of  FIGS. 1 and 2  in the interest of understanding. However, it is to be understood that the method of the flowchart  200  can also be performed using other systems and/or elements (not shown) within the scope of the present teachings. While the flowchart  200  depicts particular method steps and order of execution, it is to be understood that other embodiments that include other respective steps and/or orders of execution can also be used. Thus, the method of the flowchart  200  is exemplary of any number of other such methods within the present scope.  
      In step  202  ( FIG. 3A ), run-of-mine ore is crushed to a suitable median size. For purposes of example, it is assumed that gold-bearing, run-of-mine ore  102  ( FIG. 1 ) is crushed using a suitable crusher  104  so as to derive (define) crushed solids (i.e., crushed ore)  106  having a median size of approximately 0.375 inches in diameter. Other median sizes and/or sizing schemes for the crushed solids  106  can also be used.  
      In step  204  ( FIG. 3A ), crushed solids  106  ( FIG. 2 ) are provided directly into the mass flow reactor  110  by way of solids entry point  150  so as to fill the MFR  110  to a predetermined operating depth (i.e., vertical pile dimension) “S”. Thus, the slurry prep tank  107  ( FIG. 1 ) is assumed to be bypassed or otherwise unused. For purposes of the ongoing example, it is assumed that the MFR  110  is filed with crushed solids  106  to a depth “S” of eighty feet. Other operating depths of the crushed solids  106  within the MFR  110  can also be used. It is further assumed that the cavity volume “V” defined by the mass flow reactor  110  is such that 82,700 tons of crushed solids  106  are present when the exemplary depth “S” of eighty feet is achieved. It is important to note that at this time, no material is being extracted from the MFR  110 . Once the desired depth “S” of crushed solids  106  is established in the MFR  110 , the flow thereof is ceased at least for the time being. Also at this time or anytime while filling, any initial amount of flocculant  160  that is desired can be provided into the MFR  110 .  
      In step  206  ( FIG. 3A ), a predetermined liquid lixiviant  108  ( FIG. 2 ) is provided into the mass flow reactor  110  by way of controlled flow through one or more of the liquid entry points  152 . For purposes of example, it is assumed that a predetermined operating depth “L” of ninety feet of the lixiviant  108  (i.e., liquid) is established in the MFR  110 . Other operating depths “L” can also be used. It is further assumed that the lixiviant  108  is defined by an aqueous solution including cyanide. As in step  204  ( FIG. 3A ) above, no material is being extracted from the MFR  110  ( FIG. 2 ) at this time. Once the desired liquid depth “L” of lixiviant  108  is established in the MFR  110 , the flow thereof is ceased for the time being.  
      In step  208  ( FIG. 3A ), the crushed solids  106  ( FIG. 2 ) are reacted with the lixiviant  108  within the MFR  110  for a predetermined period of time, or dwell, so as to permit at least one material of interest to be dissolved out of the crushed solids  106  and into solution with the lixiviant  108 . Thus, the derivation of post-reaction solids  112  and pregnant leach solution  114  is underway. Also, if desired or required, the gas  158  can be controllably introduced into the mass flow reactor  110 . This dwell time (i.e., period of reaction without any extraction of post-reactions solids  112  or pregnant leach solution  114 ) can be performed for any predetermined period of time such as, for purposes of example, five hours, etc.  
      In step  210  ( FIG. 3A ), the post-reaction solids  112  ( FIG. 2 ) and the pregnant leach solution  114  (as well as substantially not-yet-reacted lixiviant  108  and crushed solids  106 ) begin to migrate through the mass flow reactor  110  in the prevailing direction “G”, by way of gravity alone. In this initial instance, such migration is generally due to settling of material due to the liquid-bath conditions present in the MFR  110 .  
      In step  212  ( FIG. 3A ), which in fact can occur just prior to, or almost simultaneously with, step  210  above, the extraction of post-reaction solids  112  ( FIG. 2 ) via one or more of the solids exits points  154  begins. The extraction of pregnant leach solution  114  by way of one or more of the liquid exit points  156  is also begun. The extraction of the post-reaction solids  112  is generally performed in a controlled fashion so that the volumetric (or mass) flow of the post-reaction solids  112  follows a predetermined pattern or scheme, defining a solids extraction flow rate. In turn, the extraction of pregnant leach solution  114  is also performed in a predetermined controlled-flow manner, defining a liquid extraction flow rate. Such solids and liquids extraction flow rates can be, respectively, substantially constant, increase or decrease linearly or non-linearly over time, etc. In short, any desired flow rate characteristic can be independently employed in regard to the extraction of post-reaction solids  112 , and any desired flow rate characteristic can be employed, up to the maximum permeability rate, in regard to the extraction of pregnant leach solution  114 . In any case, the extraction of PRS  112  and PLS  114  is performed substantially under the influence of gravity alone as previously described above.  
      Also in step  212  ( FIG. 3A ), the introduction (or addition) of crushed solids  106  ( FIG. 2 ) into the MFR  110  is performed at a rate in accordance with the extraction of post-reaction solids  112 . Furthermore, lixiviant  108  is added to the MFR  110  at a rate corresponding to the extraction of pregnant leach solution  114 . Thus, at this time, crushed solids  106  are added to, and post-reaction solids  112  are extracted from, the mass flow reactor  110  in a simultaneous fashion such that a “mass flow” or migration (substantially under the influence of gravity alone) of solid material through the MFR  110  is established and maintained for a predetermined period of time. For purposes of the ongoing example, this simultaneous flow of crushed solids  106  and post-reaction solids  112  is maintained for a period of at least of at least 3 days. Typically, the crushed solids  106  and the post-reaction solids  112  are extracted at substantially equal and/or constant rates, such that the predetermined depth “S” of solids (e.g., eighty feet, etc.) within the MFR  110  is generally maintained constant during this “simultaneous flow” period. Furthermore, lixiviant  108  is added to, and pregnant leach solution  114  (as well as any trace and/or incidental amount of PLS borne by the PRS  112 ) is extracted from, the MFR  110  in a simultaneous fashion, such that a gravity-driven mass flow or migration of liquid material through the MFR  110  is established and maintained for a period of time. For purposes of the ongoing example, this simultaneous flow of lixiviant  108  and pregnant leach solution  114  (as well as any residual amount of PLS borne by the PRS  112 ) is maintained for a period of at least 3 days. Generally, the respective flow rates of the lixiviant  108  and the pregnant leach solution  114  are controlled at substantially equal and/or constant rates, such that the predetermined liquid depth “L” (e.g., ninety feet, etc.) is maintained essentially constant within the MFR  110  during the time of simultaneous flows.  
      It is important to note that the respectively controlled flow rates of solids (i.e., crushed solids  106  and PRS  112 ) and liquids (i.e., lixiviant  108  and PLS  114 ) through the mass flow reactor  110  results in the reacting, or processing, of ore or other solid materials in a manner that is substantially continuous—rather than batch-like—in overall process operation. This means that once the desired depths (i.e., quantities) of solids “S” and liquid “L” are established in the MFR  110  (e.g., as in steps  204  and  206  above), such respective depths (or mass quantities, etc.) can be maintained essentially constant within the mass flow reactor  110 , if desired, by way of appropriate solids and liquid flow control in to and out of (that is, through) the MFR  110 . Once established, such continuous processing can be perpetuated for essentially any predetermined period of time (hours, days, weeks, months, etc.).  
      In step  214  ( FIG. 3B ), the post-reaction solids  112  ( FIG. 1 ) are routed to a screen process  120 . Therein, post-reaction solids  112  of less than a predetermined size are separated from the balance of the post-reaction solids  112 , thus defining a stream (or supply) of relatively coarse post-reaction solids  122 , and a stream (or supply) of fine post-reactions solids (or “fines”)  124 . For purposes of example, it is assumed that the screen process  120  is defined and provided such that the fines  124  are comprised of individual particles less than five-eights inch in size. Other sizing (or classifying) schemes can also be used in separating fines  124  from coarse post-reaction solids  122 . The coarse post-reaction solids  122  ( FIG. 1 ) are then routed to suitable other processing  126  such as, for example, detoxification, disposal, heaping for later processing, etc.  
      In step  216  ( FIG. 3B ), the stream of fine post-reactions solids  124  ( FIG. 1 ) are received by a centrifuge process  128  where additional pregnant leach solution (i.e., PLS  114 ) is extracted from the fines  124  resulting in a stream (or supply) of pregnant leach solution  130 . In another embodiment, (not shown), other equipment such as filters could be used instead of the centrifuge process  128 . Fine post-reaction solids exit the centrifuge process  128  and define a stream (or supply) of dried fines  136 . While such are referred to as “dried”, it is to be understood that relatively small quantities of PLS  114  may still be present on, or absorbed within, the dried fines  136 . This aspect of the dried fines  136  will be considered in further detail below.  
      In step  218  ( FIG. 3B ), the stream of pregnant leach solution  130  ( FIG. 1 ) is received by a clarifying process  132 . The clarifying process  132  removes solids from the PLS  130 , by a gravity type clarifier, a cyclonic type clarifier, by filters, or by any suitable known means, so as to derive a relatively low-solids stream (or supply) of pregnant leach solution  134 . In this way, subsequent PLS  134  processing can be performed with greater efficiency and/or efficacy as most of the solids in the solution have been removed. In some embodiments, the clarifying process  132  is omitted altogether, and the stream (or supply) of PLS  130  directly defines the stream (or supply) of PLS  134  by way of, for example, carbon columns treating dilute gold solutions.  
      In step  220  ( FIG. 3B ), the dried fines  136  ( FIG. 1 ) are (optionally) routed to a barren solution (or water) wash  140 . The barren solution wash  140  is essentially a barren solution filled vessel in which the dried fines  136  are soaked for some period of time so as to further extract (i.e., leach) relatively small or trace amounts of pregnant leach solution (i.e., PLS  114 ) from the dried fines  136 . Typically, the barren solution wash  140  is used only when the material of interest (i.e., gold, platinum, etc.) dissolved into the pregnant leach solution (i.e., PLS  114 ) is of sufficient value to economically warrant such extra processing. When used, the barren solution wash  140  derives a stream (or supply) of aqueous leachate  142  borne by the “rewetted” fine solids. For purposes of ongoing example, it is assumed that at least some of the dried fines  136  are routed to the barren solution wash  140 , where additional gold-bearing pregnant leach solution  114  is leached out of the dried fines  136  and into solution with the barren solution, thus defining the aqueous leachate  142 . It is also assumed that the fines bearing the aqueous leachate  142  are routed to other processing  138 , where the aqueous leachate  142  is separated from the fines (e.g., by way of centrifugal separation  144 , a filter arrangement (not shown), etc.) and thereafter combined with the PLS stream  134  for additional processing at step  222  below. In turn, it is further assumed that any non-washed fine solids  136  are sent to respective other processing  138  and are discarded, etc. In those embodiments (not shown in  FIG. 3B ) where the barren solution wash  140  is not used, the dried fines  136  are simply routed to other processing  138  for detoxification, disposal, etc., as desired.  
      In step  222  ( FIG. 3C ), the respective streams (or supplies) of pregnant leach solution  114  ( FIG. 1 ) and  134  are received at a pregnant leach solution process  116 . Thus, with respect to the PLS stream  114 , the heat exchanger  115  ( FIG. 1 ) is assumed to be bypassed or otherwise unused. Therein, any suitable process step or combination of steps and/or apparatus is/are used to extract at least a majority of the material of interest from the aggregate pregnant leach solution ( 114  and  134  of  FIG. 1 ). For purposes of ongoing example, it is assumed that dissolved gold is recovered from the aggregate PLS by way of adsorption, elution, electrowinning and retorting—processes known to one of ordinary skill in the mining engineering arts. The recovered material of interest (e.g., gold, etc.) is then sent on to step  224  ( FIG. 3C ) below. The residual liquid of processing the pregnant leach solution ( 114  and  134  of  FIG. 1 ) is assumed to be processed as desired by way of regeneration, destruction, containment and disposal, etc.  
      In step  224  ( FIG. 3C ), the recovered material of interest from step  222  above is finally processed as needed so as to be delivered to the market place. For purposes of example, it is assumed that retorted gold is smelted by known techniques to produce gold bullion. Other process steps can also be employed, as needed or desired, in accordance with the goal at hand. In this way, the steps  222  and/or  224  are typically performed so as to isolate at least one material of interest, as originally present in the run-of-mine ore  102  ( FIG. 1 ), in a form that can be provided to (i.e., sold within) the market. At this point, the exemplary method of the flowchart  200  is presumed to be completely described.  
      In the interest of understanding, at least some of the characteristics and advantages of the present teachings are summarized as follows:  
      a) The reaction of crushed solids with lixiviant (or other liquid) can be performed within a vessel, otherwise referred to as a mass flow reactor, as a substantially continuous process;  
      b) Solid and liquid materials migrate through, and are extracted from, a mass flow reactor substantially under the influence of gravity alone and without the use of other relevant mechanical means or forces such as, for example, driven paddles, augers, downward and/or upward liquid jetting, or vibrating, rocking, shaking, and/or rotating the mass flow reactor, and wherein gravity is not less than ninety percent of the migration-inducing force when gaseous pressure is present over the materials within the mass flow reactor;  
      c) At least some of the reaction of crushed solids with liquid within a mass flow reactor can be performed under conditions of a predetermined hydrostatic head of the liquid;  
      d) A flocculant can be used, if desired, to affect the permeability of crushed solids with respect to liquid within a mass flow reactor. In this way, liquid-on-solid contact, and the corresponding reaction between solids and liquids, can be suitably increased;  
      e) A gas can be injected into a mass flow reactor so as to oxidize or otherwise chemically affect compounds present during the reaction of crushed solids with liquid.  
      f) One or more physical and/or chemical variables can be suitably controlled within the mass flow reactor during processing, by any respectively suitable known means. Non-limiting examples of such variables include pH, Eh (i.e., electron potential in solution), temperature, viscosity, the concentration of a gas, the concentration of a liquid, etc.  
      g) A suitable inert solid can be used, if desired, to affect—increase, decrease or stabilize—one or more characteristics within a mass flow reactor during a reaction between solids and a liquid or liquids. Non-limiting examples of such characteristics include heat conductivity, heat absorption, etc.  
      It is anticipated that the invention will be embodied in other specific forms, not specifically described, that do not depart from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive, the scope of the invention being defined by the appended claims and equivalents thereof.