PROCESS FOR RECOVERY AND RECIRCULATION OF CONCENTRATED SULFURIC ACID

Description

PROCESS FOR RECOVERY AND RECIRCULATION OF CONCENTRATED SULFURIC ACID

[0001] The present invention relates to a process for recovering concentrated sulfuric acid from a wet gas and recirculating the concentrated sulfuric acid to the upstream process requiring concentrated sulfuric acid.

[0002] In the production of valuable metals such as nickel and copper, so-called sulfuric acid leaching processes are commonly used when the metals of interest exist as oxides, for example, NiO. In these processes, the oxides of the desired metals in the ore are converted into sulfates, which are soluble in water and therefore can be easily separated from the rest of the ore material and subsequently refined into the pure metal.

[0003] The acid leaching process can take various forms with regard to the ratio of sulfuric acid to ore, temperature, pressure, time and recovery of metallic sulfates.

[0004] In one of these processes for nickel production, concentrated sulfuric acid is mixed with ore powder to form a paste. The formation of nickel sulfate occurs in the paste in a digestion step and in a subsequent drying and heating step.

[0005] We have now identified an economical process for recirculating sulfuric acid by condensing concentrated sulfuric acid.

[0006] For the purposes of this application, the unit % by weight will mean weight / weight %, the unit % by volume will mean volume / volume %, and the unit ppmv will mean volume / volume parts per million.

[0007] For the purposes of this application, where gas-phase concentrations are given, they are, unless otherwise specified, given as volume / volume concentration.

[0008] For the purpose of this application, concentrations of Petition 870260059194, dated 06 / 17 / 2026, page 9 / 67 2 / 21 Sulfur (SU3) in gaseous form is stated as a % by volume of %, under the assumption that all hexavalent sulfur is present as SO3 and therefore includes SO3 as well as hydrated SO3 present as gaseous H2SO4.

[0009] For the purposes of this application, vertical and horizontal should be interpreted as allowing moderate deviation, such as less than 5° or 10° from the vertical or horizontal, respectively.

[0010] Liquid sulfuric acid, H2SO4, exists in mixtures with water in concentrations ranging from 0 to 100% by weight of H2SO4. The properties of sulfuric acid solutions depend on the concentration, both in relation to chemical reactions and to the corrosion of the material used for storing and transporting sulfuric acid.

[0011] For the purposes of this application, concentrated sulfuric acid has a concentration of 85 to 100% by weight of H2SO4. Diluted sulfuric acid has a concentration of 0 to 10% by weight of H2SO4. The concentration of sulfuric acid on the world market is 93 to 98.5% by weight of H2SO4.

[0012] A first aspect of the present invention relates to a process for the production of sulfuric acid from a process gas comprising 1 to 10% by volume of SO3 and 10-70% by volume of H2O on a non-hydrated basis, as well as 1-5,000 mg / Nm3 of particulate solids having a diameter greater than 1 µm, said process comprising the following steps: a) Condense sulfuric acid from the process gas by indirect heat exchange with a cooling medium, producing a stream of concentrated sulfuric acid, a desulfurized process gas containing sulfuric acid mist, and a quantity of heated cooling medium. b) to remove sulfuric acid mist from the desulfurized process gas in an acid mist removal step, in order to produce Petition 870260059194, dated 06 / 17 / 2026, page 10 / 67 3 / 21 a stream of dilute sulfuric acid and a clean gas, c) Recycle at least a quantity of concentrated sulfuric acid to an upstream process, such as acid leaching of mineral ore, optionally along with a quantity of said diluted sulfuric acid.

[0013] This has the associated benefit of providing a process for the economical recycling of SO3 as sulfuric acid. For specific processes, the amount of solids can be 100 mg / Nm3, 500 mg / Nm3 or 1,000 mg / Nm3. Particulate solids can typically have a diameter of less than 1 mm.

[0014] A second aspect of the present invention relates to a process according to the first aspect, further comprising the step of passing a dust-laden process gas comprising 1-50 g / Nm3 of particulate solids through a dust removal unit, such as an electrostatic precipitator, a candle filter or a cyclone, producing a stream of solids and said process gas. This has the associated benefit of providing a process that allows a dust-laden process gas stream comprising a very high amount of dust, such as 1-50 g / Nm3 or 5-30 g / Nm3.

[0015] A third aspect of the present invention relates to a process according to any of the above aspects, wherein the cooling medium is air or process gas, further comprising the step of diluting the process gas or the dust-laden process gas with a heated cooling medium stream having a temperature of 160°C to 300°C. This has the associated benefit of providing a combined heated dilute stream with a reduced risk of H2SO4 condensation.

[0016] A fourth aspect of the present invention relates to a process according to any aspect above in which the process gas contains 2 to 6% by volume of SO3 and 20 to 50% by volume of H2O in Petition 870260059194, dated 06 / 17 / 2026, p. 11 / 67 4 / 21 non-hydrated base. This has the associated benefit of providing a suitable process gas for condensing H2SO4 in concentrated form.

[0017] A fifth aspect of the present invention relates to a process according to any of the above aspects in which the condensation of sulfuric acid is carried out in a falling film condenser, wherein the process gas flows inside substantially vertical glass tubes and cooling medium outside the substantially vertical glass tubes to separate the process gas and the cooling medium, wherein the inlet temperature of the process gas is 250 to 300 °C and the outlet temperature of the process gas is 70 to 120 °C. This has the associated benefit of providing a capacitor with cost and thermal efficiency.

[0018] A sixth aspect of the present invention relates to a process according to any one of the first four aspects above, in which the condensation of sulfuric acid is carried out in an acid condenser, wherein the process gas flows out of substantially horizontal glass tubes and the cooling medium flows into substantially horizontal glass tubes to separate the process gas and the cooling medium, wherein the inlet temperature of the process gas is 220 to 300 °C and the outlet temperature of the process gas is 70 to 120 °C. This has the associated benefit of providing a condenser that is robust with respect to clogging by particulate matter.

[0019] A seventh aspect of the present invention relates to a process according to any aspect above, in which the concentrated sulfuric acid produced is 90 to 98.5% by weight of H2SO4. This has the associated benefit of providing a process that produces high-quality concentrated acid for recycling in upstream processes, such as mineralogical leaching, for example, of nickel or ore. Petition 870260059194, dated 06 / 17 / 2026, p. 12 / 67 5 / 21 copper. Ideally, sulfuric acid is at least 92% by weight of H2SO4 or 94% by weight of H2SO4.

[0020] An eighth aspect of the present invention relates to a process according to any of the above aspects in which the sulfuric acid condensation unit is equipped with a clogging-resistant defogging device, such as an electrostatic precipitator or a knitted, woven or non-woven mist filter. This has the associated benefit of preventing the release of sulfuric acid aerosol or droplets from the process. Clogging resistance can be established by a variety of means, such as dust blowing, rinsing and mechanical agitation.

[0021] A ninth aspect of the present invention relates to a process according to any of the above aspects, in which the cooling medium is air or process gas in which the heated cooling medium of the sulfuric acid condensation unit is 160 to 260 °C and is recycled to one or more upstream processes requiring combustion air and / or dilution air.This has the associated benefit of an energy-efficient process, in which thermal energy can reduce, for example, the need for fuel in upstream processes.

[0022] A tenth aspect of the present invention relates to a process according to any aspect above in which seed particles are added to the process gas to achieve a total amount of added powder particles and seed particles in the range of 1010 to 1013 particles / Nm3 of process gas / 1 % by volume of SO3 on a non-hydrated basis. This has the associated benefit of supplementing the particulate matter in the process gas so that nucleation seeds are available, leading to an appropriate number and size of sulfuric acid droplets.

[0023] An eleventh aspect of the present invention relates to a process according to any aspect above in which the Petition 870260059194, dated 06 / 17 / 2026, p. 13 / 67 6 / 21 The concentration of particulate solids in the sulfuric acid product from the acid condensation unit is 0.01 to 2.0% by weight. This has the associated benefit of recycling a quantity of material not leached with the sulfuric acid to the upstream process and reducing the amount of particles in the clean gas stream.

[0024] A twelfth aspect of the present invention relates to a process according to any aspect above in which both sulfuric acid streams produced in step a) and in step b) are recycled to the upstream process, such as acid leaching of mineral ore. This has the associated benefit of providing a process with little or no residual sulfuric acid stream and maximum sulfuric acid utilization.

[0025] A thirteenth aspect of the present invention relates to a process according to any aspect above in which at least 20% by weight, 50% by weight, 80% by weight or 90% by weight of the particulate solids with a diameter greater than 1 µm are salts of one or more metals taken from the group of Ni, Zn, U, Cu, Mo, Fe, Li, Au and rare earth metals, such as sulfate salts. This has the associated benefit of sulfuric acid contamination of such particulate solids being compatible with a process for leaching ore with sulfuric acid. In a specific embodiment, the metal with the highest concentration in said particulate solids with a diameter greater than 1 µm will also be the metal with the highest concentration in the mineral ore subjected to acid leaching.

[0026] A fourteenth aspect of the present invention relates to a process plant for carrying out the process according to any of the above claims.

[0027] In humid gases, that is, gases containing water vapor, there will be an equilibrium between gaseous SO3 and H2SO4 according to the hydration reaction: Petition 870260059194, dated 06 / 17 / 2026, page 14 / 67 7 / 21 SO3(g) + H2O(g) θ H2SO4 (g)

[0028] At high temperatures, i.e., > 400 °C, practically only SO3 will exist, while H2SO4 will be dominant at temperatures below 200 °C. In the intermediate temperature range, both SO3 and H2SO4 are present. For convenience, the sum of the concentrations of SO3 and H2SO4 are combined into a single value, assuming that the acid is in its non-hydrated state, i.e., SO3.

[0029] The drying and heating stage of the acid leaching process requires heat input to dry the slurry and heat the solids to the desired temperature, i.e., > 400 °C and up to more than 1,000 °C, depending on which chemical reactions are desired in this stage.

[0030] The heat is normally supplied by the combustion of a fuel with air as the O2 source. The drying and heating stage can, for example, be carried out in a rotary kiln, where the combustion gas sweeps through the kiln to dry and heat the slurry in the kiln. The drying stage transfers water from the slurry to the combustion gas, and the additional heating will result in the evaporation of excess sulfuric acid and the decomposition of metal sulfates. When the combustion gas exits the drying and heating stage, the water concentration may be greater than 20% by volume and the sulfuric acid vapor concentration may be greater than 2% by volume.

[0031] In another rotary kiln layout, the kiln can be indirectly burned / heated, meaning that the paste inside the rotary kiln is only in contact with a carrier gas, which can be air, a fraction of the combustion gas from indirect burning, or another gas. Indirect heating can also be provided by electric heating.

[0032] The concentration of powder in the exhaust gas of the drying and heating unit can be as high as 50 g / Nm3, the exact concentration depends on the properties of the powder and handling in the step of Petition 870260059194, dated 06 / 17 / 2026, page 15 / 67 8 / 21 drying and heating and the speed of the combustion / carrier gas. The powder will be primarily mineral, comprising at least 20% by weight, 50% by weight, 80% by weight or 90% by weight of metals to be recovered, such as sulfates or oxides of Ni, Zn, U, Cu, Mo, Fe, Li, Au and rare earth metals. The powder metals generally correspond to the metals in the ore and preferably to the metals to be produced from the ore. The upper limit of the metal content may be 2 times the lower limit, at 95% by weight, 99% by weight or 100% by weight.

[0033] The process gas temperature at the outlet of the drying and heating stage will be in the range of 250 to 400 °C for an acid leaching process, but may be higher if chemical conversion of the slurry is desired. In this case, heat exchangers may be installed to recover some of the high-temperature energy while cooling the process gas. The process gas pressure may be slightly below or slightly above atmospheric pressure, depending on the process layout.

[0034] The dry pulp will fall from the rotary kiln to be processed further, however, a fraction of the dry pulp will be carried away by the combustion / conveyor gas as dust and will leave the kiln via the drying and heating gas.

[0035] It is not desirable for such gas to be emitted into the atmosphere and therefore the gas is treated to remove sulfuric acid vapor, preferably recovering the sulfuric acid vapor as concentrated sulfuric acid, which can be recycled to the acid leaching process.

[0036] Sulfuric acid is hygroscopic in nature and, combined with the high concentration of water in the gas, the production of concentrated sulfuric acid requires careful process design.

[0037] The gas is then typically cooled by quenching to Petition 870260059194, dated 06 / 17 / 2026, p. 16 / 67 9 / 21 Cooling the gas removes soluble gases such as SO3 / H2SO4, HCl, HF, remaining dust, and gaseous metallic compounds. Quenching is typically a direct contact unit in which hot gas is directly contacted with a cold liquid, cooling the gas through a combination of sensible heat transfer and water evaporation. The cold liquid can be water, but it will usually be a dilute solution of sulfuric acid circulating in the quenching tower. Quenching types can be, for example, venturi-type contactors, packed beds, spray nozzle arrangements, and so on. To reduce the risk of clogging, dust in the gas can be removed by means of a hot electrostatic precipitator, candle filters, cyclones, or other methods.

[0038] The cooled gas typically exits the cooling unit at 50 to 70 °C and will contain some sulfuric acid mist, which is normally separated from the cooled gas in a wet electrostatic precipitator.

[0039] This clean gas will then normally be sent to a sulfuric acid plant to convert the SO2 in the clean gas into concentrated sulfuric acid, which can be recycled to the acid leaching process.

[0040] In CA 1,338,815 and WO 2008 / 064698, processes for the catalytic production of sulfuric acid from SO2 are presented. The processes involve the catalytic oxidation of SO2 to SO3 in multiple catalytic steps with intermediate cooling, followed by hydration of SO3 and condensation of H2SO4. To obtain efficient condensation, 1010 to 1013 solid particles per Nm3 per 1% of H2SO4 vapor are incorporated into the gas containing H2SO4, for example, by combustion of silicon oil. In CA 1,338,815, the seed particle size is estimated to be less than 0.6 µm.

[0041] For such catalytic production of sulfuric acid from SO2, a high concentration of mineral powder would be detrimental to the operation. Petition 870260059194, dated 06 / 17 / 2026, page 17 / 67 10 / 21 uninterrupted process, since the catalyst bed would be clogged, as the commonly used catalyst is a sticky alkaline vanadium melt in a porous oxide. The effect of this will also be that typically 95% of the mineral dust will be captured in the catalyst particles, so the amount of dust for the condenser will be very limited. Furthermore, in the production of sulfuric acid by catalytic oxidation of SO2-rich gases, such as coal flue gas, Claus process exhaust gas, or carbon black production exhaust gas, some dust may be present in the SO2-rich gases, but most of this dust will be carbon particles, which are oxidized upon contact with the alkaline vanadium melt catalyst. Therefore, the amount of dust directed to downstream condensation will typically be below 1 mg / Nm3.

[0042] For an acid leaching process, where the drying and heating stage occurs at moderately low temperatures, almost all the sulfur is found in the form of SO3 or H2SO4 and there is no need to have a dedicated sulfuric acid plant to oxidize SO2; all the sulfuric acid will be recovered in the quenching tower and the wet electrostatic precipitator. Depending on the conditions, a mixture of SO2 and SO3 may also be present in the gas leaching process, and in this case a process for condensing hydrated SO3 may be followed by any known SO2 removal process, including catalytic oxidation to SO3 and scrubbing processes.

[0043] Furthermore, if the acid is intended to be recycled to the acid leaching process in which the powder was formed, contamination with powder originating from the acid leaching process will not pose a problem, and the tolerance for contamination will be higher.

[0044] The quenching tower is not suitable for the production of concentrated sulfuric acid, as the water concentration in the drying and heating gas is high and the quenching operating temperature is low. Petition 870260059194, dated 06 / 17 / 2026, p. 18 / 67 11 / 21 In addition to the low acid concentration, the quenching operation requires substantial amounts of cooling energy, either as cooling water and / or cooling air in the acid circulating in the quenching process, or direct injection of water into the gas. The latter will increase the water concentration in the drying and heating gas, thus producing an even lower concentration of sulfuric acid, unsuitable for recycling in the acid leaching process.

[0045] In principle, sulfuric acid from the cooling tower can be concentrated in a separate unit by means of water evaporation, but this is complicated and the concentration unit requires a substantial energy input.

[0046] The present invention describes a process in which concentrated sulfuric acid, suitable for recycling in the acid leaching process, is recovered from hot gas, minimizing energy requirements, by a sulfuric acid condensation principle similar to that used in the production of sulfuric acid by catalytic oxidation of SO2-rich gases in wet gas sulfuric acid plants.

[0047] The hot gas from the drying and heating process can be conditioned by adding hot gas to dilute the gas for controlling the sulfuric acid dew point temperature and the process gas temperature, ensuring that the process gas has a suitable temperature and sulfuric acid dew point temperature for the sulfuric acid condenser.

[0048] The hot gas from the drying and heating stage may optionally also pass through a dust removal unit, such as a hot ESP, cyclone or candle filter, to remove at least a fraction of the dust from the process gas before the process gas enters the sulfuric acid condenser to reach a moderate dust load, such as below 3,000 mg / Nm3 or 5,000 mg / Nm3.

[0049] The sulfuric acid condenser is typically a Petition 870260059194, dated 06 / 17 / 2026, p. 19 / 67 12 / 21 A falling film type condenser in which the process gas containing sulfuric acid vapor is indirectly cooled as it flows upwards within vertical glass tubes. When cooled, the sulfuric acid vapor condenses and, by gravity, moves downwards and is stripped of water by the upward-moving process gas, and the sulfuric acid removed from the bottom of the acid condenser becomes concentrated and suitable for use in the acid leaching process. The cooled gas typically exits the condenser at 60 to 120 °C, which allows a substantial amount of water vapor to exit with the cooled gas while ensuring complete condensation of the sulfuric acid vapor.

[0050] Indirect cooling of the process gas is normally carried out by air or other gases flowing on the outside of the vertical glass tubes and the hot cooling air from the sulfuric acid condenser can, for example, be used as combustion air in the drying and heating stage, saving fuel in that stage, and / or as air conditioning for the drying and heating gas.

[0051] In a specific layout of the vertical falling film condenser, a dense demister will be located at the top of the condenser tube to collect and return acid droplets to the falling film condenser. In the case of substantial amounts of dust in the process gas, there is a risk that such dense demisters will become clogged with solids, although the liquid flow in the demisters should wash away the solids. In this case, a loose demister will be used to minimize the risk of dust accumulating in the demister.

[0052] Typically, defoggers are made of knitted metal or plastic wire with vacuums exceeding 95%. For high-efficiency defoggers, the vacuum is lower to allow for a larger collection area, at the cost of greater pressure drop and a higher risk of Petition 870260059194, dated 06 / 17 / 2026, p. 20 / 67 13 / 21 Defroster blockage, if there are solids in the gas.

[0053] In principle, defoggers can be omitted, but in that case, the emission of acid droplets from the falling film condenser can be substantial.

[0054] In a special layout of a sulfuric acid condenser, spray nozzles can be installed above the defogger(s) to provide intermittent washing of the defoggers in case of solid buildup.

[0055] The falling film condenser will typically have so-called nucleation control to minimize the formation of sulfuric acid mist, i.e., submicron sulfuric acid droplets, which are very difficult to collect in defoggers. Nucleation control provides particles to the process gas, for example, by combustion of silicone oil, so that the sulfuric acid vapor has available surfaces for condensation, efficiently suppressing the formation of acid mist. With dust particles already present in the hot gas, nucleation control may be superfluous and therefore can be omitted, simplifying the condensation process.Typically, the particle size is preferably in the range of 10¹⁰ to 10¹³ particles / Nm³ of process gas / 1% by volume of H₂SO₄. This ensures a balance between the number of particles and the amount of condensable H₂SO₄, forming droplets of a size suitable for collection in defoggers, and similarly, a small number of seed particles causing the spontaneous formation of many small droplets that are only collected in defoggers with low efficiency. To minimize silicone oil consumption and acid contamination of the product, the seed particle size is desired to be less than 0.1 µm. However, if the acid is intended to be recycled in the acid leaching process forming powder, there will be powder contamination originating from the leaching process. Petition 870260059194, dated 06 / 17 / 2026, page 21 / 67 14 / 21 acid will not pose a problem, and tolerance to contamination will be greater.

[0056] Inevitably, there will be some sulfuric acid mist in the cooled gas exiting the sulfuric acid condenser, and a suitable acid mist removal device is preferably installed to ensure that the clean gas emitted into the atmosphere complies with environmental legislation. Defoggers of different layouts, Brink-type defogging candles, and wet electrostatic precipitators can be used for acid mist removal. For the present application with dust in the defogging gas, a wet electrostatic precipitator will be more robust against clogging with dust particles and is the preferred technology, but Brink-type defogging candles, especially if configured with a cleaning mechanism, can also be used.

[0057] Downstream of the acid mist removal device, the clean, cooled gas can be sent to other gas cleaning units, such as an SO2 scrubber and / or a blower, before the clean gas is released into the atmosphere through a chimney. The gas cleaning unit can also be located between the acid condensation unit and the acid mist removal device.

[0058] The sulfuric acid condenser can also be supplied with horizontal tubes in which the process gas flow is on the outside of the tubes and the cooling medium flow is inside the tubes. As nucleation control does not work very well under such conditions, the outlet gas of such a condenser may require an acid mist removal device, and this is usually an integrated part of such a sulfuric acid condenser design. This design is robust against dust particles in the process gas. The concentration of sulfuric acid produced will be lower than that of the vertical falling film condenser described above, but still high enough. Petition 870260059194, dated 06 / 17 / 2026, page 22 / 67 15 / 21 for recirculation for the acid leaching process.

[0059] The sulfuric acid condenser can also be a fixed-bed type condenser, where the process gas is cooled and the sulfuric acid is condensed in a countercurrent flow with relatively hot concentrated sulfuric acid. Acid mist control does not work under these conditions, and it will be possible to configure the fixed-bed condenser to provide a suitable sulfuric acid concentration for recirculation to the acid leaching process. The choice of construction materials is very limited, as the hot concentrated acid will be very corrosive to metals, and therefore brick lining and / or fluoropolymer lining may be necessary. Figures

[0060] Figure 1 shows a process flowchart with the quenching-type condenser according to the established technology.

[0061] Figure 2 shows a process flowchart according to a preferred embodiment of the present invention.

[0062] Figures 1 and 2 consist of a schematic and sequential representation of the prior art process and the proposed process, respectively.

[0063] In Figure 1, the metal ore (1) is fed into the digestion unit (3) and mixed with sulfuric acid from a combination of fresh concentrated acid (2) and sulfuric acid (38) recycled from the quenching unit (34).

[0064] The acid ore paste formed (4) is transferred to a drying and heating unit (5), such as a rotary kiln, where the paste is dried and heated to produce a solid product of sulfuric acid-treated metal ore (8). Drying and heating are preferably carried out by combustion of a fuel (6) with combustion air (9).

[0065] The outlet gas from the drying and heating unit (10), Petition 870260059194, dated 06 / 17 / 2026, p. 23 / 67 16 / 21 containing sulfuric acid vapor, water vapor and a large amount of dust, such as up to 50 g / Nm3, is passed to an optional dust removal unit (15), such as an electrostatic separator, cyclone or candle filter, separating most of the dust in the outlet gas into a solid stream (16) and a partially dust-free outlet gas (17).

[0066] The partially dust-free outlet gas (17) enters the cooling unit (34), where the gas is cooled and the sulfuric acid and water vapor are partially condensed to form a sulfuric acid product (36). Cooling can be achieved by a combination of direct addition of water for evaporative cooling (42) and / or water / air cooling (inlet 43 and outlet 44) in the cooling unit's circulation system.

[0067] The sulfuric acid product (36) is split into a fraction, which is recycled back to the acid leaching process (38) and a fraction (40), which can be used in other processes and / or will be sent to a sulfuric acid concentration unit.

[0068] The gas exiting the quenching unit (46) will contain some sulfuric acid mist, which is separated in the wet electrostatic precipitator (48), forming a stream of diluted sulfuric acid (50) and a cleaning gas (52), which can be sent to the atmosphere or other gas cleaning units.

[0069] In Figure 2, the metal ore (1) is fed into the digestion unit (3) and mixed with sulfuric acid from a combination of fresh concentrated acid (2), recycled concentrated sulfuric acid from the sulfuric acid condensation unit (22) and optionally diluted sulfuric acid from the acid mist removal unit (28).

[0070] The acid ore slurry formed (4) is transferred to a drying and heating unit (5), where the slurry is dried and heated to produce a solid acid-treated metal ore product. Petition 870260059194, dated 06 / 17 / 2026, p. 24 / 67 17 / 21 sulfuric (8). Drying is preferably carried out by combustion of a fuel (6) with combustion air, preferably hot air from the acid condensation unit (7).

[0071] The outlet gas from the drying and heating unit (10), containing sulfuric acid vapor, water vapor and a large amount of dust, such as up to 50 g / Nm3, is optionally mixed with hot air (12) and the optionally diluted drying and heating outlet gas (14) is passed to an optional dust removal unit (15), such as an electrostatic separator, cyclone or candle filter, separating most of the dust in the outlet gas into a solid stream (16) and a partially dust-free outlet gas (17) comprising less than 5,000 mg / Nm3 of dust.

[0072] To maintain a temperature above the dew point of sulfuric acid, the dust-free gas (17) is optionally diluted with hot air via line 18 and the diluted dust-free gas (20) is then directed to a sulfuric acid condensation unit (22). The concentrated sulfuric acid from the acid condensation unit is withdrawn via line 24, cooled (not shown) and recycled to the digestion unit (3).

[0073] The cooling of the dust-free gas in the sulfuric acid condensing unit is carried out by cooling air supplied by line 32, and heated cooling air exits the acid condensing unit via line 34. A fraction of the heated cooling air is directed back to the upstream processes via line 36, and the unused heated cooling air is vented via line 35. The recycled heated cooling air (36) is optionally heated (or cooled) in heat exchanger 38 before the temperature-conditioned cooling air is directed to one or more air streams 7, 12, and 18. Depending on the process requirements, the heat exchanger may be positioned in the air streams. Petition 870260059194, dated 06 / 17 / 2026, page 25 / 67 18 / 21 individual. If deemed more beneficial, the heat exchanger can be replaced by other heating means, for example, an electric or fuel-fired backup heater.

[0074] The outlet gas from the condensation unit (26) is sent to a sulfuric acid misting unit (28), in which the sulfuric acid mist is separated from the outlet gas as diluted sulfuric acid in stream 30 and optionally recycled to the digestion unit (3). The mist-free outlet gas (32) is emitted to the atmosphere, optionally passing through other gas cleaning units and / or a process gas blower (not shown). Examples

[0075] This example compares the operating conditions for the basic quenching solution with the operating conditions for the sulfuric acid condensation process according to the invention.

[0076] In this example, Table 1 shows operational data for basic quenching designs according to the prior art and a proposed design with a sulfuric acid condensation unit. The process gas composition is 4.1% by volume SO3, 42% by volume H2O, 300 °C, atmospheric pressure and 1,000 ppmv of sulfuric acid in the outlet gas of the cooling and condensation unit, where the outlet gas of the drying and heating unit has a flow rate of 26,000 Nm3 / h. The dew point temperature of the sulfuric acid in this process gas is approximately 270 °C.

[0077] In the inventive layout design, 5,000 Nm3 / h of heated dilution air are added to lower the dew point temperature of the sulfuric acid to protect the construction materials in the sulfuric acid condensation unit.

[0078] In Example 1, the basic cooling-type solution, the outlet gas from the drying and heating unit is cooled by direct injection of water for evaporative cooling, and in Example 2, by means Petition 870260059194, dated 06 / 17 / 2026, page 26 / 67 19 / 21 of circulating sulfuric acid, cooled by cooling water in the circulation circuit. Table 1 provides the basic operating parameters for the different process layouts.

[0079] It is clear from the data that the cooling-type operation will produce sulfuric acid with a lower concentration than with the sulfuric acid condensation unit, more than doubling the volume of intermediate-strength sulfuric acid produced in Examples 1 and 2 compared to the concentrated sulfuric acid of Example 3. The concentration range of 40 to 50 wt% H2SO4 is commonly too weak to provide an efficient leaching process, and therefore the addition of concentrated acid is necessary, so it will not be possible to recycle all the acid to the upstream process. Furthermore, this low concentration is not used in the commercial acid market, where a minimum of 93 wt% H2SO4 is required.

[0080] It is conservatively assumed that 1,000 ppmv of acid mist (100% by weight H2SO4) in the outlet gas will be found in the primary acid production units. The very dilute acid from wet ESP will significantly decrease the mixed acid concentration of the two production units. However, the 69% by weight H2SO4 of the inventive layout will still be high enough for the acid leaching process and all acid production can be recycled, thus eliminating a potential problem with residual acid production.

[0081] With regard to process gas cooling, basic cooling with evaporative cooling is quite efficient, as no external cooling is required. Water consumption is 2,050 kg / h, most of which will be found in the sulfuric acid product, thus decreasing the sulfuric acid concentration and increasing the mass flow rate.

[0082] Using only cooling water in cooling and Petition 870260059194, dated 06 / 17 / 2026, page 27 / 67 20 / 21 assuming a 10 °C increase in the cooling water temperature, the cooling water flow rate will be 687,000 kg / h, which is a very large flow rate. The sulfuric acid concentration will be slightly higher than for direct water cooling.

[0083] The sulfuric acid condensation unit of Example 3 requires atmospheric air as a cooling medium; about half of the cooling airflow can be used as dilution air before the condensation stage and combustion air in the drying and heating stage. The latter will decrease the fuel requirement in the drying and heating unit. Table 1: Description Unit Example 1 Example 2 Example 3 Outlet gas from drying / heating unit Nm3 / h 26,000 26,000 26,000 Addition of dilution air Nm3 / h 0 0 5,000 Concentration of sulfuric acid product % by weight 41 46 96 Sulfuric acid production Kg / h 11,250 9,970 4,725 Cooling of process gas in the condensing unit kW - 7,980 3,610 Cooling water flow Kg / h 2,050 - - Cooling water flow Kg / h - 687,000 - Cooling air flow Nm3 / h - - 53,400 Petition 870260059194, dated 06 / 17 / 2026, page 28 / 67 21 / 21 Description Unit Example 1 Example 2 Example 3 Concentration of wet ESP acid % by weight 6.3 6.3 6.2 Production of wet ESP acid Kg / h 1,610 1,530 2,020 Cooling water flow kg / h 100,000 101,000 133,000 Water in wet ESP exhaust gas % by volume 11 7 28 Total acid production Kg 12,870 11,500 6,745 Mixed acid concentration % by weight 36 41 69

Claims

CLAIMS 1. Process for the production of sulfuric acid from a process gas comprising 1 to 10% by volume of SO3 and 10 to 70% by volume of H2O on a non-hydrated basis, as well as 1-5,000 mg / Nm3 of particulate solids having a diameter greater than 1 µm, said process comprising the following steps: a) condensing the sulfuric acid from the process gas by indirect heat exchange with a cooling medium, producing a concentrated sulfuric acid stream, a desulfurized process gas containing sulfuric acid mist and a quantity of heated cooling medium, b) removing the sulfuric acid mist from the desulfurized process gas in an acid mist removal step in order to produce a dilute sulfuric acid stream and a clean gas, c) recycling at least a quantity of concentrated sulfuric acid to an upstream process, such as acid leaching. of mineral ore,optionally along with a quantity of said diluted sulfuric acid, characterized in that said particulate solids comprise at least 20% by weight of salts of one or more metals from the group of Ni, Zn, U, Cu, Mo, Fe, Li, Au and rare earth metals.

2. Process according to claim 1, characterized in that it further comprises the step of passing a process gas laden with dust comprising 1-50 g / Nm3 of particulate solids through a dust removal unit, such as an electrostatic precipitator, a candle filter or a cyclone, producing a stream of solids and the process gas.

3. Process, according to claim 1 or 2, characterized in that the cooling medium is air or process gas, Petition 870260059194, dated 06 / 17 / 2026, page 30 / 67 2 / 3, further comprising the step of diluting the process gas or the powder-laden process gas with a stream of heated cooling medium having a temperature of 160 °C to 300 °C.

4. Process, according to any one of claims 1 to 3, characterized in that the process gas contains 2 to 6% by volume of SO3 and 20 to 50% by volume of H2O on a non-hydrated basis.

5. A process according to any one of claims 1 to 4, characterized in that the condensation of sulfuric acid is carried out in a falling film condenser, wherein the process gas flows inside vertical glass tubes and the cooling medium flows outside the vertical glass tubes to separate the process gas and the cooling medium, wherein the inlet temperature of the process gas is 250 to 300 °C and the outlet temperature of the process gas is 70 to 120 °C.

6. A process, according to any one of claims 1 to 4, characterized in that the condensation of sulfuric acid is carried out in an acid condenser where the process gas flows out of horizontal glass tubes and cooling medium inside the horizontal glass tubes to separate the process gas and the cooling medium, wherein the inlet temperature of the process gas is 220 to 300 °C and the outlet temperature of the process gas is 70 to 120 °C.

7. Process, according to any one of claims 1 to 6, characterized in that the concentrated sulfuric acid produced is 90 to 98.5% by weight of H2SO4.

8. Process, according to any one of claims 1 to 7, characterized in that the condensation of sulfuric acid is carried out in a sulfuric acid condenser equipped with a clogging-resistant defogging device, such as an electrostatic precipitator or a knitted, woven or non-woven mist filter.

9. A process, according to any one of claims 1 to 8, characterized in that the cooling medium is air or process gas, wherein the heated cooling medium of the sulfuric acid condensation unit is 160 to 260 °C and is recycled to one or more upstream processes that require combustion air and / or dilution air.

10. Process, according to any one of claims 1 to 9, characterized in that seed particles are added to the process gas to achieve a total amount of added powder particles and seed particles in the range of 1010 to 1013 particles / Nm3 of process gas / 1% by volume of SO3 on a non-hydrated basis.

11. Process, according to any one of claims 1 to 10, characterized in that the concentration of particulate solids in the sulfuric acid product of the acid condensation unit is 0.01 - 2.0 % by weight.

12. Process, according to any one of claims 1 to 11, characterized in that both sulfuric acid streams produced in step a) and step b) are recycled to the upstream process, as acid leaching of mineral ore.

13. A process according to any one of claims 1 to 12, characterized in that at least 50% by weight, 80% by weight or 90% by weight of said particulate solids with a diameter greater than 1 µm are salts comprising one or more metals taken from the group of Ni, Zn, U, Cu, Mo, Fe, Li, Au and rare earth metals, such as sulfate salts.

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