AU690199B2 - In-situ chemical reactor for recovery of metals and salts - Google Patents

Description

In-situ Chemical Reactor for Recovery of Metals And Salts Background of the Invention This invention relates to tL. recovery of valuable metals and mineral salts from fresh and salt water bodies and from various sedimentary deposits and rocks.

Valuable metals and salts are found in nature either as minerals in sediments and/or rocks or as dissolved ions in fresh water and/or brine. Ores have to be processed physically and chemically to produce commercial products. Normally the ores are mined, milled, and refined in factories.

In arid regions such as the Qaidam Basin of Northwest China or in the Dead Sea region of Israel, the potassium-rich brines are mostly chloride brines, and they are also enriched with magnesium, sodium, and other ions. The current methods of recovering potassium from such brines have the disadvantage that the final product of evaporation, after NaCl is removed, is a potassium mixed salt (KC1.MgC1 2 .6H 2 KC1 has to be separated from the mixture in a factory, and 15is the refining process is costly. Furthermore, the final product is not always pure enough to be used as a chemical fertiliser.

Summary of the Invention It has now been discovered that va,luable products can be directly obtained by in-situ mining without having to resort to excavation and milling, and with a 20 minimum of factory refining. The invention of the "in-situ reactor" makes it possible to remove magnesium ions from brines, so that commercially pure KCI can be precipitated directly from brine through evaporation. Not only is the process more economical, but a further advantage is that the KC1 so precipitated is sufficiently pure to be used as chemical fertiliser.

25 The invention is directed to a process for the economic recovery of metals from fresh water, brine and unconsolidated sediments or from rocks. The process provides for recovery of ores in-situ through chemical reaction of a metal-bearing (or metal-extracting) fluid and a solid in an in-situ reactor. The fluid flows through the in-situ reactor under a hydrodynamic gradient. The ore in the fluid can be fractionated or the metal in the solid can be extracted by chemical reaction between the fluid and solid phases.

The invention is particularly suitable for the recovery of potassium and lithium from brine in certain arid regions, such as Northwest China, Israel, Chile, Bolivia, and western North America, or for the mining of gold and other metals found in dark or organic-rich shales, such as those in the Carlin (Nevada) type of gold bearing deposits. The invention further optimises the efficiency of a chemical exchange in in-situ reactors as fluid is induced to mainly move vertically upward through a chemical filter layer, with a resultant faster flow rate because the cross- IN:\LIBC10720:JOC ~I -I 2 sectional area A of such vertical flow is much larger than that of lateral fluid movement of in-situ mining processes currently in use.

The type of "in-situ reactor" employed depends on whether the metal or salt is present in solid form or as dissolved ions in solution.

If the metal or salt is contained in sediment or rock, the metal bearing rock is converted into an "in-situ reactor", so that the metal in the reactor can be dissolved by an injected fluid which is induced to flow vertically upward into collecting ponds, where the fluid is pumped out for refining by conventional methods.

Brief Description of the Drawings Fig. 1 is a cross-sectional view of the strata at the site of an in-situ reactor suitable for use in processing ore bearing fluids.

Fig. 2 is a cross-sectional view of an in-situ reactor suitable for use in processing ore bearing fluids.

Fig. 3 is a cross-sectional view of the reactor of Fig. 2 showing the chemical filter layer in place.

Fig. 4a is a flow chart showing the treatment of brine (high K/Mg (wgt%) ratio).

Fig. 4b is a flow chart showing the treatment of brine (very low K/Mg (wgt%) ratio).

Fig. 5 is a cross-sectional view of an in-situ reactor suitable for use in processing solid ore bearing rock.

Fig. 6 is a cross-sectional view of a variation of the in-situ reactor shown in Fig. Referring to Figs. I and 2 of the drawings, the figures show a cross-section of the strata in an in-situ reactor 10 wherein 11 is a layer of salt and/or sediment, 12 is a sand aquifer, 13 is the bed or base of the reactor and 14 is water, i 25 ho the height of the groundwater table; hi the height of the water-level in the in-situ reactor; Sh112 the height of the bottom of the pond; and 0* h4 the height of the sand (aquifer).

Referring to Fig. 3 of the drawings, the figure shows the in-situ reactor of Fig. 2 30 with chemical filter layer 15 in place, h 0 the height of the groundwater table; hi the height of the water level in the in-situ reactor; h2 the height of the surface of the chemical layer in the reactor; h3 the height of the bottom of the reactor; (hO-hl):(h2-h4) the hydrodynamic gradient; (hil-h2) the water depth in the reactor; (h 2 -h3) the thickness of the chemical filter layer in the reactor: (hO-h3) the depth of the excavation pit; hS 1 T h4 the height of the upper surface of an aquifer; IN: L113AA14990.KWW -s 1 h2-h4 the distance of fluid movement through the reactor; and K transmissibility, in empirical constant with a value related to the permeability of the porous medium through which fluid flows.

Referring to Figs. 5 and 6 of the drawings, the figures show an in-situ reactor 20 for use in processing solid, ore bearing rock wherein 21 is the bed rock, 22 is the water permeable processing zone which may also contain oxidised stone or rock, 23 is water and 24 are bore holes, ho the height of the groundwater table; hi the height of the water level in the in-situ reactor; h 2 the height of the bottom of the pond; h 3 the height of the bottom of the reactor; (ho-h):(h 2 -h 3 the hydrodynamic gradient; hi-h2 the water depth in the reactor; h 2 -h 3 the vertical distance of the water or fluid movement; and S 1is K transmissibility, an empirical constant with a value related to the permeability of the host rock through which fluid flows.

Description of the Preferred Embodiments •If the metal or salt is contained in fresh water or brine in an "in-situ reactor" may be constructed so that the composition of the groundwater or brine is modified S as it flows upward into and filters through a reactive chemical filter layer. The reactor in this case is an open pit 10 having its bottom below the local water table 14 (Figs. 1 and The bottom of the pit is lined with the chemical filter layer which, in some instances, may cover a layer of salt and/or sediment 11 or gravel or gravelly sand 12 (Fig. The composition of chemical filter layer 15 selected for in-situ reactor 10 is determined by the ionic-fractionation desired. The S" chemical employed is dependent upon whether: the metal to be recovered is extracted by the chemical as the fluid is filtered through the chemical filter layer; or one or more undesirable ions are extracted or exchanged and thus removed from the solution by the chemical as the fluid is filtered through the chemical filter layer.

In the first i stance, the metal extracted by the chemical filter layer can be taken out of the in-situ reactor and refined by conventional means. In the second instance, the metal-bearing fluid, with one or more undesirable ions removed from the solution, can be introduced to other facilities where the metal is recovered by conventional means. The purpose of effecting chemical reactions in an in-situ reactor is to minimise the need for factory refining and thus to reduce production costs.

IN:\LIBC100720:JOC L -p- The in-situ reactor is constructed so that the flow rate can be varied to effect optimum chemical reaction between a fluid and a solid as 'he fluid flows through solid. The flow rate Q, or volume per unit time, depends upon three factors, namely: i) the transmissibility of the flow K; ii) the hydrodynamic gradient of the flow, (ho-h 1 )/(hz-h 4 where ho is the height of groundwater table, h, the height of the water level within the pit, h 2 the height of the surface level of the chemical layer in the pit, and h4 the height of the source bed (aquifer) of the water or brine, as noted in Fig. 3; iii) the cross-sectional area A normal to the path of flow.

The rate is determined by the Darcy-Hubbert-Hsu formula Q K [(ho-h 1 2 -h 4

A.

The in-situ reactors are so-designed that the flow rate is to be regulated through adjustment of the three factors.

The hydrodynamic gradient of the in-situ reactors can be easily regulated.

The hydrodynamic potential difference (ho-h 1 can be varied through a change of h 1 when fluid is being pumped out of the in-situ reactor so that the fluid-level within the reactor (hl) stand3 at the level desired, or through an increase of potential height hO when fluid is pumped under increased hydraulic pressure into a gravel layer at the base of the "in-situ reactor".

The transmissibility factor K is related to the permeability of the solid, or solid mixture in the filter. Transmissibility is necessarily changed because of chemical reaction within in-situ reactors. The permeability of the chemical filter layer in the in-situ reactor could, however, be maintained or even increased by a S. 25 mixing of soluble salt with the chemical in the reactor, or through other means.

i.o To recover metals gold or uranium) from black shale or oil shale, leaching fluid must be injected into a host rock which is permeable and oxidised.

The fracturing and shale-burning methods, which have until now been applied only to oil production to render the metalliferous host rocks oxidised and permeable, are used for the recovery of metals from black shale, or oil shale.

In selecting witer supplies for production of KC1 and lithium carbonate production, as adapted for local conditions in the Qaidam Basin of China, it is preferred that the area to be selected is one where the sulfate concentration is low.

The brine should be essentially a chloride of Mg, K, and Na, with a high lithium content.

Since the production requires substantial freshwater or slightly brackish water to dilute the brines during production, a borehole is drilled to an aquifer below the surface in the selected regior and the water is stored in an adjacent reservoir.

The procedures employ chemical fractionation in evaporating ponds and/or in in-situ reactors. For recovering K and Li from Mg rich chloride brines, the IN :\LIC 100720:JOC I -LI I~L~BB~ l 1 9 51 I ~I following ponds and reactors, numbered according to their functional utility, are employed.

In-situ Reactor 1 serves to remove Mg by chemical reaction.

In-situ Reactor 2 serves to convert chloride colution into bicarbonate/chloride solution.

Evaporating Pond 1 serves to precipitate NaCI from brines.

Evaporating Pond 2 serves to precipitate KCI from brines.

Evaporating Pond 3 serves to precipitate K/Mg mixed salt from brines.

Evaporating Pond 4 serves to precipitate Mg as chloride from brines.

Evaporating Pond 5 serves to precipitate mixed salts enriched in Li.

For recovery of K and Li from brines in the Qaidam region of China, the process is shown diagrammatically by Figures 4a and 4b. The steps in the process consist of: 1. Removing Mg For brines with K:Mg (wgt%) ratio of about 1:1, the brine can be fed directly from the underground source to in-situ Reactor 1 as described below (Fig. 4a).

Natural brines commonly have a K:Mg (wgt%) ratio considerably less than 1, eg.

Qaidam brines have a ratio of 1:20. A brine with a low K:Mg (wgt%) ratio is first prepared through the evaporative precipitation of KCI.MgCI 2 .6H20 by conventional means in Evaporating Pond 3 (Fig. 4b). The residual brine enriched with Mg is drained from the evaporating pond, thus removing much of the Mg from the system (step 1) and S* can be used for Li-production as described afterwards.

Evaporating Pond 3 is lined with a gravel or coarse sand layer at the bottom and isolated from ground contact by plastic sheets or other water barrier means and if S necessary, with an overlying chemical filter layer. After the KC1.MgCl2.6H20 is 25 precipitated above the gravel (and/or the chemical filter), a chemical solution is pumped S into the gravel. Such a chemical solution can be made from the dissolution of trona mud by fresh or brackish water. Alternatively, a carbonic acid solution could be pumped into the gravel. The solution rises to acidify a layer of powdered limestone between the gravel S and the K/Mg mixed-salt precipitate, where dissolved bicarbonate is to be used as the 30 chemical agent to remove Mg from the mixed salt. As the solution rises under the pump pressure into the K/Mg precipitate, KCI is dissolved from the mixture, while the Mg reacts with the solution to form hydrous magnesium carbonate (MgCO3.xH20). Thus, Evaporating Pond 3 serves the function of an in-situ Reactor 1 to remove Mg from the brines (production of KC1). Because of the dissolution processes, the flow of the solution through the chemical filter is not impeded, because the permeability of the solid medium is increased by dissolution.

IN)L1113AAI4990:KWW S. I The filtered brine, which now contains mostly dissolved KC1 and NaCI (or CaC12) from in-situ Reactor (converted from Evaporating Pond is pumped into an Evaporating Pond 1 for further processing in step 2.

After the chemicals which line the bottom of the in-situ Reactor are completely converted into hydrous magnesium carbonate, the residue in the reactor can be removed. If necessary, a layer of new chemical is placed above the gravel layer in the reactor. The pit can again be used Ls an Evaporating Pond 3 for the precipitation of KCI.MgCI2.6H 2 0. The magnesium carbonate from the reactor can be processed to make magnesium cement, or periclase (MgO), as local needs demand.

2. Removing Na Evaporating Pond 1 is constructed according to local climatic conditions to provide appropriate evaporation.

Brine which contain mostly dissolved K and Na chloride from in-situ Reactor 15 1 is introduced into and concentrated in Evaporating Pond 1 by natural evaporation until NaCI is almost completely precipitated from solution.

3. Recovering KC1 The residual brines following step 2 are transferred to Evaporating Pond 2 for further natural evaporation. KCI is precipitated from the brine and is recovered (step KCI precipitation is terminated if and when KC1 MgCI 2 .6H 2 0 is about to precipitate, as the Mg-removal may not have been complete.

4. Production of Li Mg is removed from brines drained from Evaporating Pond 3. The residual brine which is drained (during step 1) from Evaporating Pond 3 is transferred to ~'5s Evaporating Pond 4 for further evaporation (step Mg Cl 2 is precipitated and thus the residual brine is depleted in Mg and enriched in Li.

Conversion of a chloride brine into a bicarbonate solution The residual brine following step 4 is transferred to a water reservoir. A dilute chloride solution is prepared by mixing the residual brine with fresh or ;o slightly brackish water to provide a dilute solution having a concentration of several percent.

In-situ Reactor 2, having dimensions similar to in-situ Reactor 1 (=converted Evaporating Pond is constructed with a water reservoir for introduction of dilute chloride solution into Reactor 2. The bottom of the in-situ Reactor is lined with clean gravel or coarse sand to facilitate movement of water through the chemical filter.

The filter should be a layer of trona mud to convert the dilute chloride solution into a bicarbonate solution through a gradual dissolution of the trona mud.

6. Recovery of lithium carbonate IN:\LIBC100720:JOC II_ 7 The bicarbonate solution from in-situ Reactor 2 is introduced into Evaporation Pond 5 and evaporated to dryness so that Mg, Na, K are mainly precipitated as chlorides, and Li mainly as carbonate.

Th 3ride is removed by dissolution. The residue should be carbonate of Li, mixed with Mg and Na carbonates. The lithium carbonate can be refined by conventional methods.

The various detailed procedures to install an in-situ reactor for the exploitation of metals and salts are exemplified by the following examples: Example 1 Recovery of potassium salt through direct precipitation of KCI from Mgrich brines Where chloride brines are enriched with potassium, sodium, and magnesium, the process involves direct KCI precipitation by evaporation resulting in the removal of magnesium, the removal of sodium, and the recovery of KCI.

15 The process requires that a minimum of one in-situ reactor and two evaporating ponds be constructed for serial production. The specifications and their functions are described as follows: Removal of Mg 2 in in-situ Reactor 1 In-situ Reactor 1 having dimensions of 33m x 33m in area and a depth of 20 about Im or more below the groundwater table, or about 3m below the surface is constructed. The pit wall is lined with plastic or with fabric to make it impermeable. The bottom of the pit is lined with a layer of gravelly sand 5-10cm S• thick. The gravelly sand is covered by a chemical filter layer of trona mud or dolomite powder about 15-20cm thick; the filtering layer serving to remove Mg 25 from brine. The thickness of the filter can vary so as to obtain optimum rate of flow.

The brine filling the open pit should be approximately several meters deep, but the water level should be lowered by pumping when movement into the pit is desired. The flow race is maintained at a slow enough rate through the chemical filter so for optimum Mg removal: i) Use trona mud, either as a filler or as an aqueous solution filtering through K/Mg salt to remove magnesium, as previously described, the trona mud being particularly suitable for use with brines low in sulfate ion; ii) Use powdered limestone to be acidified by carbonic acid as the agent to remove Mg as described previously.

If the efficiency of the Mg removal is too low because the flow rate is too high, the brines may be pumped to a brine-reservoir (tower) to be reintroduced into the gravel layer for recycling until the K:Mg ratio is increased to a value greater than 5:1.

IN:\LIBC100720:JOC

I-

8 If the flow rate is too low, as the permeability of the chemical in the filter is decreased by Mg/Na replacement, the trona mud (or dolomite) is mixed in the filtering layer lining the pit with NaCI, so that the filter contains a mixture with NaCI in the mud. Water reservoirs, several meters high and a few meters in diameter, should then be constructed, with pumping system to facilitate mixing with brines to be introduced into the gravelly sand at the bottom of the in-situ reactor. Alternatively, fresh water can be introduced directly into the gravelly sand below the in-situ reactor (driven by the gravity head of the water reservoir) into the gravelly layer to dilute the brine to keep its concentration considerably .o below NaCl saturation. Brine thus diluted, filtering through the trona mud NaCI mixture, should dissolve NaCIl in the trona mud so that the x.rmeability of the filter can be kept at an optimum value.

Another means to facilitate the filtering of brine through the chemical filter layer is to form an interlaminated deposit of the reacting filter chemical and 15 permeable sand in the bottom of the pit; the interlamination can be produced through an alternate deposition of a layer of reacting filter chemical and a layer of sand. This arrangement is particularly suitable if there is considerable cementation caused by chemical reactions as a brine is filtered through the chemical filter layer.

After the chemical filter layer is no longer reactive with the magnesium ion of the brine, new chemical filter material can be placed into the pit, after the spent chemical is removed.

The chemical for the filter in the in-situ reactor is selected because it has the ability to effect ion-exchange to remove magnesium ion from brines. Sodium carbonates (Na 2 CO3.NaHC03) are particularly suitable, because of their 'fast 25 reaction rate and because the sodium ion exchanged could eventually be removed as NaCl by fractional evaporation. For the sake of economy, a trona mud (Na 2

CO

3 .NaHCO 3 2H 2 0) rather than the pure compound is preferred. To economise even further, the use of powdered limestone is preferred, and it is especially suitable for brines with high concentrations of sulfate ion which could then be precipitated by the calcium released by ion-exchange from the limestone.

Removal of Na+ ions in Evaporating Pond I The filtered brine from in-situ Reactor 1 is pumped into Evaporating Pond 1.

The dimension of the pond depends upon the brine inflow rate from the in-situ Reactor, the evaporation rate, and the production volume. Typical evaporating ponds in Qaidam have dimensions of 100m x 300m x 2m.

By means of solar evaporation, sodium ions in the brine are removed by precipitation as sodium chloride.

Recovery of KC1 in Evaporating Pond 2 The residual brine from Evaporating Pond 1 is drained into Evaporating Pond 2, which may have dimensions similar to those of pond 1.

IN:LIBCIO0720;JOC I ~dl Ib id ~s Potassium ion from the brine is precipitated as KCl because of the relatively high K:Mg ratio of the brine. Recovery should proceed until the K:Mg ratio of the brine is reduced so that KCl-MgCl 2 .6H 2 0 is about to be precipitated.

Recovery of KCl.MgCI2.6H 2 0 in Evaporating Pond 3 s If the residual brine from the Evaporating Pond 2 still contains some K ions, it can be introduced into an Evaporating Pond 3 having similar dimensions.

Potassium ion in this brine of a higher K:Mg ratio is precipitated as KCI.MgCI 2 .6H 2 0, which can be recovered and refined in the factory for KC1 as is currently done.

The procedure to recover KCI.MgCl2.6H 2 0 is particularly suitable for those salt-works where facilities are available to separate potassium and magnesium from the mixed salt.

Example 2 Recovery of lithium salt through precipitation of lithium carbonate from 15 K-Mg rich chloride brines In arid regions such as the Qaidam Basin of Northwest China, potassium-rich brines enriched in magnesium and sodium, may contain lithium in sufficient quantity so that lithium can be economically recovered. Lithium is presently extracted by solar evaporation from fresh water or brines. The Qaidam brines are, however, chloride rich, also containing in some instances significant concentrations of sulphate-ions. Such chloride brines may be converted into bicarbonate solution so that lithium can be recovered as lithium carbonate by means of the "in-situ reactors". Before the brine composition is changed by chemical reactions in the insitu reactor, KCI can be recovered as a commercial by-product by the process 25 described in Example 1.

The procedure to install "in-situ reactors" for lithium recovery is as follows: Removing Na and recovering KCI to produce residual brine enriched in Mg and Li KC1 is precipitated as a by-product of lithium production, according to the process described in Example 1. During Step 1 of the process, the residual brine in Evaporating Pond 3 of KCI MgCl 2 .6H 2 0 precipitation is depleted in K, enriched in Mg and somewhat enriched in Li, as described previously.

Removing Mg The residual brine from Evaporating Pond 3 is transferred to Evaporating Pond 4 for further natural evaporation. The residual brine, after MgCl2 precipitation is depleted in Mg and further enriched in Li, as described previously.

Converting chloride brine into dilute solution IN:\LIBC100720:JOC a -r ~JI I~L The residual brine from Evaporating Pond 4 is transferred to a water reservoir. A dilute chloride solution is prepared by mixing the residual brine with fresh or slightly brackish water to provide a dilute chloride solution.

Converting a chloride solution into a chloride/bicarbonate solution.

The dilute chloride solution is injected into an in-situ Reactor 2.

In-situ Reactor 2 is constructed with dimensions similar to those of in-situ Reactor 1, with a water tank, where evaporated brine from Evaporating Pond 4 has been diluted to produce a dilute chloride solution. This solution is then introduced into the Reactor 2. The bottom of this in-situ reactor should be lined with clean gravel to facilitate movement of water upward through the filter. The hydrodynarnic gradient influencing the flow rate could be adjusted by pumping water out of the pit of the in-situ Reactor 2.

The chemical filter layer lining the bottom of the reactor pit should be a layer of bicarbonate salt. The dilute chloride solution from the water tank near in-situ is Reacto "ould flow under its gravity head, or be pumped, into the gravel layer at the very base of tie in-situ reactor. The solution then ascends through the chemical filter layer and enters the pit. Through the dissolution of the carbonate salt in the filter, the dilute solution becomes a saturated bicarbonate solution, with eoooo subordinate chloride and sulfate ions.

Sodium carbonates, such as trona muds, are recommended as a filtering chemical for use in in-situ Reactor 2 because of the high solubility and fast S dissolution rate. Powdered limestone (CaCO 3 can be used as the filtering chemical if the dilute solution prepared from the dilution of brines from Evaporating Pond 4 is acidified by carbonic acid to increase the solubility and S. 25 dissolution rate. The use of calcium carbonate is not only economical, it also has sea. 0 the advantage of depleting the sulfate concentration of the solution.

e) Recovery of Lithium carbonate The bicarbonate solution from in-situ Reactor D is introduced into Evaporating Pond E and evaporated to dryness so that Mg, Na, K are precipitated mainly as chlorides, and Li mainly as carbonate.

The chloride is removed by dissolution. The residue should be a carbonate of Li, mixed with Mg and Na carbonates. The lithium carbonate can be refined by conventional method.

Example 3 Recovery of Gold from Carlin (Nevada)-type Deposits.

Organic-rich metalliferous rocks contain appreciable amounts of disseminated gold and associated metals, such as silver, mercury, arsenic, antimony, etc., have been called the Carlin-type deposit. Black shales containing appreciable amount of disseminated uranium, and associated metals such as vanadium, molybdenum, N:ALIBCI10720:JOC nickel, etc., have been called the Chattanooga-type deposit. These organic-rich metalliferous sedimentary rocks (shales, mudstones) are relatively impermeale.

The Carlin gold deposit was discovered and first mined in the 1960s. Those ores, containing 7 or 10 grams of gold per ton in oxidised, leached rocks, could be mined by conventional methods of excavating the metalliferous rocks and extracting the gold from the excavated and mined ores by dilute (10 parts per million) cyanide solutions. The current mining processes are, however, so costly that the gold deposits below the oxidised, leached zones cannot be economically mined. Mineral reserves of low-grade gold are, how 'er, immense. Nevada, for lo example, was estimated in 1990 to have a reserve of 3900 metric tons. With the process of the present invention, many such low-grade deposits can be economically recovered.

The reasons why the Carlin-type deposits below the oxidised, leached zone cannot be recovered by conventional practices are tlreefold: the ore-bearing rock is too impermeable -or injected leaching solutions to penetrate into the ore body; the ore deposit contains too much organic matter and/or metallic sulfides S which render ineffective the leaching solutions; the hydrological framework of the region may lead to contamination of groundwaters by leaching solutions injected into the ore body.

Recovery of desired metals such as gold from the Carlin or Chattanooga type deposits can be accomplished by first fracturing and retorting organic-rich shale, ie., shale burning using presently available means and then converting the orebearing host rock into an in-situ reactor so that the leaching solution can be injected 25 into the reactor to dissolve the metals present therein. The in-situ reactors are constructed so that the flow path of injected fluids is controlled and thile solvents used for leaching ore metals do not contaminate or pollute groundwaters.

The procedure for working Carlin-type gold deposits, as an example, is described as follows: Fracturing and retorting organic shale The current methods of shale burning, developed for the purpose of extracting hydrocarbons from oil shales, are first applied to a deposit. A cavity is excavated underground where the rock can be ignited and into which oxygen, and in some instances fuel, are introduced to sustain the shale burning. Suitable processes are described in US 3 894 769, 4 043 595, 4 162 808, 4 182 552, 4 24 100, 4 436 344 and 4 444 256. To increase the porosity and permeability of the rock for more effective shale burning, various methods of explosion fracturing and hydrofracturing have been employed. Suitable processes are described in US 4 085 971, 4 210 366, 4 239 286, 4 522 260, 3 917 345, 4 487 260, 4 444 258, 4 522 265, 4 869 322, 5 228 510, 4 487 260 and GB 1 482 024.

IN:\LIBC100720:JOC -rm I Lls I 12 Thus, through a combination of current methods of fracturing and shale burning, an impermeable ore-bearing, organic-rich, host-rock can be converted into a porous and permeable oxidised "in-situ reactor" as hereafter described.

A borehole is drilled to depth z. Fluid is pumped under high pressure to a zone t, z meters below the surface to fracture the rocks in the zone by hydrofracturing. Fracture surfaces will radiate from the borehole, and flammable material will be pumped into the hole to ignite the burning of organic-rich shale.

Oxygen is pumped into the hole to sustain the burning, and the organic material in the rock is the fuel for the fire. Additional fuel can be introduced if the organic matter in the rock is not sufficient. The zone of "shale burning" between t and z meters below the surface can be controlled by the so-called "floor-block material" as described in US 4 478 282. Holes can be drilled on the periphery of the shaleburning zone to release the exhaust gases produced by shale burning.

Hydrocarbons produced by burning can be collected through the application of conventional methods such as described in US 4 369 842. The shale burning can Sbe extended from the original borehole outward until the entire ore-body to be exploited is burnt.

The porous and permeable burnt rock, surrounded on all sides and surrounded below by impermeable, organic-rich rock which is not burnt, is the in-situ reactor, S 2C into which leaching solution can be injected.

ii) Solution mining by leaching fluid moving under hydrodynamic gradient through the in-situ reactor.

The current solution-mining methods employed to process such shales inject leaching fluid into poi us and permeable strata, and the fluid moves laterally under 25 a pressure gradient. Boreholes are drilled on the peripher, of the injection zone, and leaching fluid is pumped into the holes under high pressure. The fluid flows then into a borehole at the centre of the zone, where the ore-bearing solution is collected and pumped out for refining.

The present invention introduces a method of moving fluids vertically upward through a mass of burnt, but still not very permeable rock. Boreholes for injecting leaching solution are drilled on the periphery of the zone of shale burning, ie., the in-situ reactor. As shown in Figs. 5 and 6, instead of one collecting borehole in the centi:,, one or more shallow collecting ponds are dug above the burning zone.

By lowering the water level within the pond, a vertical hydrodynamic gradient is produced, so that the injected fluid is induced to move upward into the pits. The hydrodynamic gradient influencing the rate of the flow can be varied by lowering the water-level within the ponds (by pumping water out of pond); the greater the level of water in a pond beneath the groundwater table, the greater is the hydrodynamic gradient and thus rate of the vertically upward flow movement. The rate can further be adjusted by varying the pressure of injection-fluid. Because of IN:\LIBC100720:JOC ~pl I 13 the much greater cross-sectional area normal to the path of vertical flow, the qaantity of leacning fluid flowing vertically upward is much more than that flowing laterally, and the leaching is rendered more efficient.

To extract gold from the Carlin-type of deposit, very dilute cyanide solution has to be used. Although a concentration of lOppm is so small that it could not lead to great health hazard, the toxicity of the fluid is nevertheless so notorious that in-situ solution mining of gold is commonly prohibited because of fear of groundwater contamination by cyanide. The present invention has the advantage that the injected fluid is forced to move through the porous and permeable in-situ reactor to the collecting ponds in the centre of the zone of shale burning. Hardly any injected fluid could penetrate into the impermeable, organic-rich host rock surrounding the in-situ reactor. The negligible amount of the injected fluid that might move sideways into the unoxidised organic-rich host rock is immediately .etoxified, because cyanide solution is easily neutralised by the organic compounds in the organic-rich host rock. Solution mining by injecting fluids into an in-situ reactor will, therefore, not constitute an environmental hazard. Furthermore, since the ores are not excavated but extracted by solution, the mine areas will not be polluted by the dumping of tailings. Instead, the collecting ponds can be refilled and seeded in the depressions into which groundwater flows.

o iii) Solution containing ore-metal, such as gold, is collected and pumped out of collecting ponds to be processed in factory by conventional refining methods.

Although the present invention has been described with pretense and embodiments, it is to be understood that modifications and variations may be resorted to without departing from the scope of the invention, reference being had 25 to the appended claims for a full definition of the scope of the invention.

IN:\LIBCI00720:JOC I i

Claims (16)

1. A process for recovering salts and metals from solid or fluid ore-deposits comprising inducing hydrodynamic flow of a salt- or metal-bearing solution through a chemical filter layer into a natural or artificial basin having walls and a floor constructed on a site bearing desired metals or salts, said chemical filter layer being located on said floor, said floor of said basin lying below the groundwater table and the flow rate is regulated through a change of the hydrodynamic gradient, to promote chemical reaction between the fluid and the chemicals in the basin and thereafter separating the reactor product.

2. The process according to claim 1 wherein the hydrostatic gradient is changed _y lowering the water level in the basin.

3. The process according to claim 1 wherein the hydrostatic gradient is changed by elevating the groundwater table.

4. The process according to any one of claims 1 to 3 wherein said solution flowing through chemical layer on the floor of said basin is rich in dissolved ions wherein the undesirable ions are removed by the chemical reaction between the fluid and the chemical layer.

The prccess according to any one of claims 1 to 3 wherein said solution flowing through said chemical filter layer on the floor of said basin is ich in dissolved ions wherein the desired ions are extracted by said chemical filter layer.

6. The process according to claim 4 wherein the ore deposit through which the fluid flows is oxidised.

7. The process according to any one of the preceding claims wherein said solution is a leaching solution induced to flow through the solid ore deposit to extract S.:2 25 desired metals and salts from the ore.

S8. The process according to any one of the preceding claims wherein a shale burning method is applied to a sol;' ore bearing body to reduce the resistance of said ore :bearing body to fluid movement and to oxidise said ore bearing body.

9. The process according to any one of the preceding claims wherein said 30 solution for extracting ore is positioned within an impermeable rock basin, thereby avoiding contaminated groundwater. z

10. The process according to claim 8 wherein fuel is injected into the burning .zone to assist spontaneous burning.

11. The process according to any one of the preceding claims wherein the chemical layer at the bottom of said basin contains a mixture of soluble salt which is dissolved by the fluid flowing through, wherein said chemical layer is kept permeable.

12. The process according to any one of the preceding claims wherein trona mud or limestone is used as the chemical to remove Mg-ion in a brine so that potassium- exploitation in the form of direct KCI precipitation by evaporation is possible. L NB4K 'r 7' f IN:\I,IBAA14990:KWW r 0 )O M r L~h r~l 111 -1

13. The process according to claim 5, wherein lithium is contained in chloride solution, and brine is converted into a bicarbonate solution through reaction with trona or other carbonates in the chemical layer at the bottom of the basin so that lithium could eventually be precipitated as a carbonate and be refined by conventional method.

14. The process of claim 1 wherein the chemical filter layer is trona mud or limestone, to convert a chloride solution into a chloride/bicarbonate solution.

A process for recovering salts and metals from solid or fluid ore-deposits, substantially as hereinbefore described with reference to any one of the examples.

16. Salts and metals recovered from solid or fluid ore-deposits by the process of any one of claims 1 to Dated 18 February, 1998 Tarim Associates for Scientific Mineral Oil Exploration AG Patent Attorneys for the Applicant/Nominated Person SFPUSON FERGUSON *ee *9 09 i*« 9 o. S *i IN:\I.I13AAj49Y)0:KWW In-situ Chemical Reactor for Recovery of Metals and Salts Abstract An "in-situ reactor" is provided to facilitate recovery of metals and salts such as potassium, lithium, gold from salt-bearing natural waters, sediments, and rocks by passing a fluid containing such metals and salts through a reactive chemical bed placed at the bottom of a reactor, the metal and salt bearing fluid flowing through the reactive chemical bed to react with the active components to produce a fluid from which the metals and salts can be more easily extracted. In a cross-section of the strata in an in-situ reactor [11] is a layer of salt and/or sediment, [12] is a sand aquifer, [13] is the bed or base of the reactor and [14] is water, [ho] is the height of the groundwater table; [hi] is the height of the water-level in the in-situ reactor; is the height of the bottom of the pond; and [h 4 is the height of the sand (aquifer). *S Gee o 4 555* IN:\LIBC100720:JOC