Production of H2S For Efficient Metal Removal From Effluents

Abstract

Method and apparatus pertaining to the production of hydrogen sulfide using sodium salts recycle. Sodium sulfate is reacted with a carbon containing stream to produce sodium sulfide and carbon dioxide. The sodium sulfide is blended with elemental sulfur and water. The blend is subjected to elevated temperatures and pressures to result in the production of hydrogen sulfide and sodium sulfate. A mixing apparatus, such as a bubble column reactor, has been found to be especially useful. The hydrogen sulfide can be used for removing metal from effluents.

Claims

1. A method to extract metals in a liquid stream containing at least one metal, comprising the steps of: flowing gaseous hydrogen sulfide (H.sub.2S) into a mixing apparatus containing the liquid stream; wherein the gaseous hydrogen sulfide and the liquid stream are mixed under conditions sufficient to extract the at least one metal.

2. The method of claim 1, whereby the mixing apparatus is comprised of one or more bubble column reactors.

3. The method of claim 1, whereby the hydrogen sulfide (H.sub.2S) gas is produced electrochemically.

4. The method of claim 3 further comprising: combining a make-up stream of Na.sub.2SO.sub.4 with a Na.sub.2SO.sub.4 liquor recycle stream, and directing the combination into a Na.sub.2SO.sub.4 concentrator.

5. The method of claim 4, wherein the concentrator is designed to extract water to thereby increase a Na.sub.2SO.sub.4 concentration.

6. The method of claim 5, wherein the concentrated Na.sub.2SO.sub.4 is then directed through a pump, into a Na.sub.2SO.sub.4/Na.sub.2S converter.

7. The method of claim 6, wherein natural gas flows in conjunction with the Na.sub.2SO.sub.4.

8. The method of claim 6, wherein the converter operates at a temperature from about 1000° C. to about 1100° C.

9. The method of claim 6 wherein Na.sub.2S is produced and a by-product is CO.sub.2.

10. The method of claim 6 wherein the Na.sub.2S is directed into a prep taken along with an appropriate amount of a water for a stoichiometric solution.

11. The method of claim 10 wherein a high-pressure pump is used to pressurize the solution.

12. The method of claim 11 wherein the stream is blended with another water stream configured to facilitate heat recovery of reaction products.

13. The method of claim 12 wherein the heat recovery is facilitated using an interchanger device.

14. The method of claim 12 wherein the blended stream flows through a heater and into a first H.sub.2S reactor along with a molten elemental sulfur stream.

15. The method of claim 14 wherein the molten elemental sulfur is produced by blending a sulfur stream and a recycle sulfur stream then pumping the composite of these two streams into a sulfur tank.

16. The method of claim 14 wherein the molten elemental sulfur is pumped out of the sulfur tank using a jacketed high-pressure positive displacement pump and directed into the first H.sub.2S reactor.

17. The method of claim 14 wherein the first H.sub.2S reactor is equipped with an agitation or mixing device.

18. The method of claim 14 wherein the first H.sub.2S reactor operates at a temperature of about 100° C. to about 250° C. and a service pressure of about 20 bar to 50 bar.

19. The method of claim 14 wherein the first H.sub.2S reactor is configured to work in cascade mode where the overflow from the first reactor is directed into a second reactor.

20. The method of claim 19 wherein the second reactor is also equipped with an agitation or mixing device; and operates at about the same temperature and pressure as the first reactor.

21. The method of claim 14 wherein each of the first and second reactors produces hydrogen sulfide.

22. The method of claim 1 whereby a bioreactor is used to generate H.sub.2S.

23. The method of claim 17 wherein the agitation or mixing device comprises a bubble column reactor.

24. The method of claim 9 wherein the CO.sub.2 is captured by a geopolymer based material.

25. The method of claim 9 wherein the CO.sub.2 is used to activate a geopolymer based material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is an embodiment of recycling/production process.

[0017] FIG. 2 is an alternate embodiment of a recycling/production process.

[0018] FIG. 3 displays a basic flow process.

[0019] FIG. 4 represents details of a feed system (H.sub.2S).

[0020] FIG. 5 displays the effect of bubble size.

[0021] FIG. 6 is a diagram showing a H.sub.2S precipitation process.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In one embodiment, as represented in FIG. 1, a make-up stream, 1, of Na.sub.2SO.sub.4 is combined with a Na.sub.2SO.sub.4 liquor recycle stream, 2, and directed into a Na.sub.2SO.sub.4 concentrator, 3. The concentrator is designed to extract a significant amount of water, 4, that increases the concentration of Na.sub.2SO.sub.4. This concentrate stream is then directed through a pump, 5, into the next unit operation. Natural gas, 6, is also permitted to flow in conjunction with the Na.sub.2SO.sub.4 concentrate. These two streams are directed into a Na.sub.2SO.sub.4/Na.sub.2S converter, 7, which operates at high temperatures of about 1000-1100° C., where “about” is defined as +/−10%. The natural gas provides the carbon source for the conversion reaction whereby Na.sub.2S becomes the preferred product. A stream of CO.sub.2, 8, is produced as a co-reaction product and is sent to the vent stack.

[0023] The Na.sub.2S is directed into a prep tank, 9, into which an appropriate amount of water, 10, is injected to prepare an appropriate stoichiometric solution. This solution is then pressurized using a high-pressure pump, 11. This stream is then blended with another water stream, 29, which is specifically incorporated to facilitate heat recovery of reaction products using an interchanger device. This Na.sub.2S and water stream then flows through a heater, 12, and into the H.sub.2S reaction system.

[0024] A sulfur stream, 13, is blended with a recycle sulfur stream, 14. A composite of these two streams is then pumped into a sulfur tank, 15. The sulfur will melt inside the H.sub.2S reactor. There is no need to maintain a sulfur temperature of about 120° C. outside of the reactor. This elemental molten sulfur is pumped out using a jacketed high pressure positive displacement pump, 16, and directed into the H.sub.2S reaction system.

[0025] The Na.sub.2S-water stream and the molten elemental sulfur stream are directed to flow into the first H.sub.2S reactor, 17. This reactor is equipped with an agitation device, 18, that ensures the maintenance of finally dispersed sulfur in the Na.sub.2S-water medium. The H.sub.2S reactor operates at a temperature of 200-250° C. and a service pressure between 20-50 bar. The H.sub.2S, which is a product of the reaction, leaves the reactor through line 19. The H.sub.2S reactor, 17, is configured to work in a cascade mode where the overflow from this reactor is directed into the next reactor through line 20. This H.sub.2S reactor, 21, as noted is working in a cascade mode using the overflow from the first reactor, 17. This reactor is also equipped with an agitation-dispersion device, 22, which ensures homogeneity of the reaction. Hydrogen sulfide, the reaction product, leaves through line 23. The merged H.sub.2S lines from reactor 17 and 21 flows through a backpressure control valve, 24. The depressurized H.sub.2S stream, 25, is then piped for its appropriate use.

[0026] The hot liquids leaving the two H.sub.2S reactors are combined as stream, 26. This stream primarily comprises of Na.sub.2SO.sub.4, a small amount of unreacted Na.sub.2S, unreacted sulfur and unreacted water. It first flows through the tube side of a heat interchanger, 27. Water, stream 28, flows through the shell side of this interchanger to maximize the pick-up of heat. This hot water stream 29, is redirected back into the H.sub.2S reactor cascading system. The cooled reactor effluent stream, 30, then flows into a centrifuge that is specifically designed to separate the sulfur slurry component from the Na.sub.2SO.sub.4 liquor component. The sulfur slurry component, 32, is then sent into a dehydrator, 33, where the water is boiled out as stream 34 leaving behind sulfur in a molten condition. This sulfur is pumped back into the main sulfur tank, 15.

[0027] Leaving the centrifuge, 31, is the Na.sub.2SO.sub.4 liquor recycle stream, 2, that is directed to the Na.sub.2SO.sub.4 concentrator. This stream undergoes concentration and flows into the Na.sub.2SO.sub.4 to Na.sub.2S converter that closes the sodium salt recycle loop. In another embodiment, as represented in FIG. 2, a make-up stream, 1, of Na.sub.2SO.sub.4 is combined with a Na.sub.2SO.sub.4 liquor recycle stream, 2, and directed into a Na.sub.2SO.sub.4 concentrator, 3. The concentrator is designed to extract a significant amount of water, 4, that increases the concentration of Na.sub.2SO.sub.4. This concentrate stream is then directed through a pump, 5, into the next unit operation. Natural gas, 6, is also permitted to flow in conjunction with the Na.sub.2SO.sub.4 concentrate. These two streams are directed into a Na.sub.2SO.sub.4/Na.sub.2S converter, 7, which operates at high temperatures of around 1000-1100° C. The natural gas provides the carbon source for the conversion reaction whereby Na.sub.2S becomes the preferred product. A stream of CO.sub.2, 8, is produced as a co-reaction product and is sent to the vent stack or, in some embodiments, the CO.sub.2 is captured by a geopolymer based material and may be used to activate the geopolymer based material. Geopolymers are inorganic, typically ceramic, alumino-silicate forming long-range, covalently bonded, non-crystalline (amorphous) networks. Typical examples of a geopolymer material includes raw materials used in the synthesis of silicon-based polymers that are mainly rock-forming minerals of geological origin.

[0028] The Na.sub.2S is directed into an agitated Na.sub.2S solution and sulfur slurry prep tank, 9. Finally ground, comminuted elemental sulfur, 10, is pneumatically transported into the prep tank, 9. A recycle sulfur stream, 12, is also continuously blended into the slurry pump tank, 9. A stream of water emanating from interchanger 15 is also continuously introduced into the prep tank. The product from the Na.sub.2S solution and sulfur slurry prep tank is pressurized using a high-pressure pump, 13. High pressure slurry solution stream, 14, then flows through an interchanger, 15, where it picks up any available heat from the stream, 11, that is flowing into the prep tank. The warmed slurry solution stream, 16, then flows through a heater, 17, that brings the entire stream up to the necessary temperature for initiating and conducting the downstream reactions.

[0029] The Na.sub.2S-sulfur/water stream is directed to flow into the first H.sub.2S reactor, 19. This reactor is equipped with an agitation device, 20, that ensures the maintenance of finally dispersed sulfur in the Na.sub.2S-water medium. The H.sub.2S reactor operates at a temperature of 200-250° C. and a service pressure between 20-50 bar. The H.sub.2S, which is a product of the reaction, leaves the reactor through line 21. The H.sub.2S reactor, 19, is configured to work in a cascade mode where the overflow from this reactor is directed into the next reactor through line 22. This H.sub.2S reactor, 23, as noted is working in a cascade mode using the overflow from the first reactor, 19. This reactor is also equipped with an agitation-dispersion device, 24, which ensures homogeneity of the reaction. Hydrogen sulfide, the reaction product, leaves through line 25. The merged H.sub.2S lines from reactors 19 and 23 consolidate as line, 26 and flow through a backpressure control valve, 27. The depressurized H.sub.2S stream, 28, is then piped for its appropriate use.

[0030] The hot liquids leaving the two H.sub.2S reactors are combined as stream, 29. This stream primarily comprises of Na.sub.2SO.sub.4, a small amount of unreacted Na.sub.2S, unreacted sulfur and unreacted water. It first flows through the tube side of a heat interchanger, 30. Water, stream 31, flows through the shell side of this interchanger to maximize the pick-up of heat. This hot water stream, 32, is directed to the interchanger, 16, and from there becomes line 11 that flows into the prep tank, 9. The cooled reactor effluent stream, 33, then flows into a centrifuge, 34, that is specifically designed to separate the sulfur slurry component from the Na.sub.2SO.sub.4 liquor component. The sulfur slurry component, 35, is then recycled using pump, 36, and becomes stream 12 that flows into prep tank, 9.

[0031] Leaving the centrifuge, 34, is the Na.sub.2SO.sub.4 liquor recycle stream, 2, that is directed to the Na.sub.2SO.sub.4 concentrator. This stream undergoes concentration and flows into the Na.sub.2SO.sub.4 to Na.sub.2S converter that closes the sodium salt recycle loop.

NON-LIMITING EXAMPLES

[0032] In one embodiment the hydrogen sulfide is generated electrochemically. Generating H.sub.2S in an electrochemical reactor whereby one can:

[0033] 1. put elemental sulfur in a protic ionic liquid (like pyridinium phosphate) and heat to T>90 C to melt the sulfur;

[0034] 2. insert a cathode made of platinum or copper or steel or graphite;

[0035] 3. insert a hydrogen anode (like hydrogen bubbled into a container with an inert anode inside an inverted Teflon cup. The anode inside the cup could be platinum wire or a dimensionally stable anode (DMA, which is Ru-oxide on titanium) or platinized graphite (platinum plated on graphite paper), etc.;

[0036] 4. A power supply is connected with the negative electrode connected to the cathode and the positive terminal connected to the anode; and

[0037] 5. as current passes sulfur should form H.sub.2S at the cathode as shown below: [0038] S+2e.fwdarw.S.sup.−2 (which goes to H2S in the presence of H+) cathode reaction and hydrogen should form proton at the anode [0039] H.sub.2.fwdarw.2H++2e− anode reaction so the net reaction is [0040] H.sub.2+S.fwdarw.H.sub.2S

[0041] Hydrogen can be from tank hydrogen or can be made on demand by the electrolysis of water by controlling current. With adequate H.sub.2 then H.sub.2S should also be supplied on demand by controlling the current.

[0042] In another embodiment the hydrogen sulfide can be produced using bio-reactors and feed into a mixing system or apparatus.

[0043] In another embodiment, use of proprietary bubble column reactors (BCR) can be done. In an example of its operation, an acid mine effluent has been tested at a site, with an average flow rate of 100 m3/day, and a concentration of 720 ppm of Fe, 21 ppm of Cu and 258 ppm of Zn at pH 2.5. The purpose of this setup was to try to reduce the concentration of metals and neutralization of the effluent. This is accomplished by producing H.sub.2S through a plant.

[0044] In one embodiment, hydrogen sulfide and dosing in BCR columns with the following operating conditions of the plant is performed: [0045] Cond. Operation [0046] Temperature 160-200° C. [0047] Pressure 100-200 psi [0048] H2S flow 10-30 L/min [0049] The conditions of the BCR columns is: [0050] Number of Columns 20 [0051] Effluent flow 100-150 m3/day [0052] Dosage H2S 10-30 L/min [0053] Effluent pH treated 6-7

Example 1: Design of Reactor

[0054] Capacity of 150 Kg/day H2S (Sufficient capacity to treat effluent, 20% excess) [0055] 2 batch reactors made of Ni alloy [0056] Internal nickel coating and graphite seals [0057] 316L alloy capacitor [0058] 9000 watt heating system [0059] Temperature and pressure safety system [0060] Semi-automatic instrumentation and control [0061] Compact modular installation, surface 2.0×3.2 m

Example 2: Design of BCR Columns

[0062] 20 columns maximum treatment capacity of 150 m3/day [0063] Control and Instrumentation [0064] Compact modular installation, surface 1.5×6.5 m or 1 Multi filter bag housing BFS [0065] Reagent pumping and dosing system operational details: [0066] Operation: Continous [0067] Effluent Fluid: 7 L/min. [0068] pH-rxc: 4-7 (NaOH) [0069] Neutralization pH 7 [0070] [Fe]ini, (mg/L): 720 [0071] [Cu]i ni, (mg/L): 21 [0072] [Zn] ini, (mg/L): 257