An improved method of concentrating fluorosilicic acid

Abstract

The present disclosure relates to a method for concentrating fluorosilicic acid from a first liquid stream comprising fluorosilicic acid. In one implementation, the solution comprising fluorosilicic acid and a gaseous stream comprising silicon tetrafluoride is introduced into a first reactor. The first reactor reacts to form the products and separates the products into at least one intermediate gas stream and at least one intermediate liquid stream. The at least one intermediate liquid stream is then introduced into at least one additional reactor. At least one product of the reactor is then separated using the at least one additional reactor. The at least one additional reactor separates the at least one product into at least a final liquid stream comprising fluorosilicic acid. The fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first liquid stream.

Description

AN IMPROVED METHOD OF CONCENTRATING FLUOROSILICIC ACIDTechnical Field

[0001] The present disclosure generally relates to a method of concentrating fluorosilicic acid (FS A). In particular, and without limitation, the present disclosure relates to concentrating FSA using a series of draft tube stirred tank reactors, each stirred tank reactor including at least one axial impeller in the upwards or downwards direction. The present disclosure relates to an apparatus comprising draft tube stirred tank reactor(s) configured to improve gas-liquid phase mixing within the vessel while silica particles remain in suspension, without negatively impacting the desired reactions.Background

[0002] FSA finds uses across many different technology areas, especially as a precursor to chemical manufacturing. Much of FSA is used a reagent to convert alumina into aluminum trifluoride which can be used as an additive for the production of aluminum. Additionally, FSA may be used to refine lead. FSA may also be converted into a variety of salts, which are useful in producing porcelains, concretes, insecticides, phosphors, and wood preservation agents.Another important application of FSA is for the production of silicon tetrafluoride and hydrofluoric acid.

[0003] In most cases the concentration of the FSA will determine the feasibility of preparing these other compounds. Many known methods of producing FSA do not produce FSA at a high enough concentration to be economically feasible. If FSA is not produced at a high enough concentration, additional processing must be taken to further refine the acid which incurs large additional manufacturing costs. Additionally, many known methods of concentrating FSA are difficult or impractical to scale effectively.Summary

[0004] The inventors discovered an improved method of concentrating FSA. In one embodiment, the present disclosure is a method for concentrating FSA, comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product; separating the first product into at least one intermediate incoming liquid stream containing silica solids and at least one final outgoing gaseous stream; feeding the at least one intermediate incoming liquid stream- which optionally contain silica solids and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream comprising fluorosilicic acid and solid silica particles and at least one first gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

[0005] In another exemplary embodiment, the present disclosure is a method for concentrating FSA through a reactor system comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product; separating the first product into at least one intermediate outgoing liquid slurry stream and at least one final outgoing gaseous stream; feeding the at least one intermediate incoming liquid slurry stream and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid slurry stream and anintermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid slurry stream comprising fluorosilicic acid and solid silica particles and at least one first gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

[0006] In another exemplary embodiment, the present disclosure is method for concentrating FSA through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising: reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product; separating the first product into at least one intermediate outgoing liquid slurry stream of the at least one liquid slurry stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid slurry stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid slurry stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicicacid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

[0007] In another exemplary embodiment, the present disclosure is method for concentrating FSA through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising: reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product; separating the first product into at least one intermediate liquid slurry stream of the at least one liquid stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

[0008] As used herein, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise.Brief Description of the Drawings

[0009] The accompanying drawings, which comprise a part of this specification, illustrate several embodiments and, together with the description, serve to explain the principles disclosed herein.

[0010] FIG. 1 is a flow diagram of the apparatus according to one embodiment.

[0011] FIG. 2 shows a block flow diagram of an anhydrous hydrogen fluoride process, such as one within which an apparatus according to one or more embodiments can be disposed.

[0012] FIG. 3 shows a less granular description of the FSA Concentration step from FIG. 2.

[0013] FIG. 4 shows a less granular description of the STF Production sub-portion of the STFProduction / HF Generation step from FIG. 2.

[0014] FIG. 5 shows a less granular description of the HF Generation sub-portion of the STF Production / HF Generation step from FIG. 2.

[0015] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate disclosed embodiments and, together with the description, serve to explain the disclosed embodiments. The drawings are not necessarily to scale. Certain dimensions, for example, may be exaggerated for purposes of clearer illustration.Detailed Description of the Illustrative Embodiments

[0016] To begin the process, an FSA solution and gaseous silicon tetrafluoride are introduced into a reaction zone of the reactor, shown as E-3 in Figure 1. The FSA solution can comprise from about 8 to about 35 mass percent of FSA based on the total mass of the FSA solution, such as, for example, from about 15 to about 30 mass percent, from about 20 to about 25 mass percent, and from about 22 to about 24 mass percent.

[0017] An incoming gas stream comprises the gaseous silicon tetrafluoride. The incoming gas stream can comprise from about 96 % to about 100 % silicon tetrafluoride, such as, for example, from 98 % to about 100 % silicon tetrafluoride and from 99 % to about 100 % silicon tetrafluoride. In some embodiments, the incoming gas stream comprises 99 wt% of silicon tetrafluoride, such as, for example, at least 99.1 wt% of silicon tetrafluoride, at least 99.2 wt% of silicon tetrafluoride, at least 99.3 wt% of silicon tetrafluoride, at least 99.4 wt% of silicon tetrafluoride, at least 99.5 wt% of silicon tetrafluoride, at least 99.6 wt% of silicon tetrafluoride, at least 99.7 wt% of silicon tetrafluoride, at least 99.8 wt% of silicon tetrafluoride, and at least 99.9 wt% of silicon tetrafluoride.

[0018] Ordinarily, the reaction produces heat and thus requires cooling. Cooling may be achieved through use of a cooler, chiller, or heat exchanger. The cooler, chiller, or heat exchanger may be configured to absorb the heat of reaction partially or fully. In some embodiments, the cooling is achieved using an external cooler where the at least one cooler, chiller, or heat exchanger is located externally with respect to the reaction vessel. In other embodiments, the cooler, chiller, or heat exchanger are located within or internal to the reaction vessel. In some embodiments, cooler, chiller, or heat exchanger may be configured as a cooling coil.

[0019] The FSA from the reactor, E-3, is sent to the reactor, E-2. The FSA stream at this step has increased FSA concentration as compared to the incoming stream. As was described above, the FSA enters as a liquid and is concentrated by reacting the incoming STF gas with water which produces more FSA according to at least formula (1) below. Additionally, the hydrolysis reaction produces solid SiO particles. These SiCh particles remain suspended in the solution while the STF gas undergoes intense mixing with the FSA solution resulting in greater reactionrates with only a small amount of SiO2falling out of the liquid mixture. The resulting FSA stream is sent to the reactor, E-l. The resulting STF stream is sent to the reactor, E-3.3SiF4+ 2H2O 2H2SiF6+ SiO2Formula (1)

[0020] In one embodiment, a dilute stream of FSA is fed into a first vessel in a counter current manner with respect to a small stream of STF. The first vessel contains at least one axial impellor operating either upwards or downwards through a draft tube. The draft tube may be located in-the top, bottom, or center of the vessel. By using at least one draft tube, the SiO2particles remain in suspension while the mass transfer is enhanced between the gaseous STF and liquid FSA, improving reaction conversion into STF. The stream of STF enters the first vessel which then mixes with the dilute stream of FSA, where STF is hydrolyzed into FSA resulting in a greater concentration of FSA. The resulting FSA stream flows to a second vessel in which a larger flow of STF gas enters (i.e., larger than the small stream of STF incoming into the first vessel). The small stream of STF gas is either passed to a more dilute vessel of FSA, or water, or removed from system and scrubbed to ensure it is not released to atmosphere.

[0021] The process may be repeated. A more concentrated FSA stream is taken to subsequent reactors with ever larger streams of STF. Each of these reactors, however, operates in the manner described above. When FSA of a desired concentration has been produced, the stream containing that FSA is reacted with a flow of FSA that comes from the STF removal column.

[0022] For pedagogical use, three reactors are described, however, fewer or more reactors may be utilized. There may be between 2 and 10 reactors, such as, for example, from between 3 and 9 reactors, from between 3 and 7 reactors, and from between 3 and 5 reactors. Each reactor may be further subdivided into multiple reactors.

[0023] In some embodiments, the residence time in any of the reactors ranges from about 1 minute to about 60 minutes, such as, for example, from about 5 minutes to about 30 minutes.

[0024] Generally, the FSA and silicon tetrafluoride streams flow in a counter current fashion. In other words, for example, FSA generally flows from reactor E-l to reactor E-2 and then to reactor E-3 while silicon tetrafluoride generally flows from reactor E-3 to reactor E-2 and then to reactor E-l.

[0025] In some embodiments, the first reactor is operated at a pressure above atmospheric pressure. In other embodiments, the first reactor is operated at or below atmospheric pressure.

[0026] The FSA stream from the reactor, E-2, is sent to the reactor, E-l . As described above, the entering STF stream is reacted with water to produce FSA, rendering a more concentrated FSA stream. This FSA stream additionally contains SiOa particles which are kept well mixed and in a slurry.

[0027] The concentrated FSA stream is sent to a filter to separate the silica particles from the FSA solution. In some embodiments, the filter may be filtering press, rotary vacuum filter, belt filter or the like. Filtered silica may be disposed of, further processed, or sold.

[0028] In some embodiments, at least one intermediate liquid stream exiting the reactor, E-l, comprises solid silica particles. In some embodiments, the solid silica particles are suspended in the at least one intermediate incoming stream. In some embodiments, the at least one intermediate liquid stream comprises a slurry.

[0029] In some embodiments, each sequential liquid stream exiting a reactor comprises a greater amount of solid silica particles as compared to liquid streams exiting upstream reactors. For example, the at least one intermediate liquid stream exiting the reactor, E-2, comprises a greater amount of silica particles compared to the at least one intermediate liquid stream exitingthe reactor, E-l. Additionally, the at least one final liquid stream exiting the reactor, E-3, comprises a greater amount of silica particles compared to the at least one intermediate liquid stream exiting the reactor, E-2.

[0030] The concentrated FSA solution is sent to the STF Generator. The FSA solution is heated to between about 150 and about 250 °F, such as, from example, between about 160 and about 240 °F and between about 180 and about 230 °F. At the temperatures described, the FSA decomposes with STF, containing some HF and H2O, and is sent to the STF Removal column. The reaction is shown as Formula 2:H2SiF6^ SiF4+ 2HF Formula (2)

[0031] Sulfuric acid flows downward through the STF Generation column. The concentration of sulfuric acid in the sulfuric acid solution ranges from about 90% to about 99%, such as, for example, from about 92%o to about 98%, from about 94% to about 98%, and from about 96% to about 98%. The sulfuric acid washes the HF and water out of the STF stream. The STF stream is sent to the first, highest concentration, of the FSA reactors. The sulfuric acid / HF / water solution from the STF Removal column is sent to the STF generator as both a heat source and an acid catalyst for the STF Generation reaction. A final liquid stream from the STF Generator is sent for further processing.

[0032] Without being bound to a particular theory, in some embodiments, at least the gaseous silicon tetrafluoride reacts in the reaction zone, resulting in a greater amount of FSA produced compared to the FSA inputted. This intermediate product is then separated into a gaseous and liquid stream for further refining of the FSA. In other words, the FSA mass concentration of the liquid stream inputted into the reactor is less than the FSA mass concentration of the liquid stream leaving the reactor. In some embodiments, the liquid stream leaving the reactor is anintermediate product which is fed into at least one subsequent reactor and separator. In some embodiments, the intermediate product is separated into a gaseous and liquid stream using at least one bubble column reactor, trickle bed reactor, or fluidized bed reactor. In some embodiments, the liquid stream comprising FSA leaving the reactor is not further refined.

[0033] In some embodiments, the final liquid stream comprising FSA may comprise FSA at a concentration of about 35 weight percent or greater based on the total mass of the final liquid stream, such as, for example, from about 35 weight percent to about 50 weight percent and from about 40 weight percent to about 45 weight percent.

[0034] According to the present disclosure, the reaction is facilitated using a draft tube impellor reactor. Without being bound to a particular theory, a draft tube impellor reactor facilitates conversion into FSA through intimate contact between the gas and liquid of the reactor while keeping the SiO? suspended. In some embodiments, the intimate contact influences the rate of conversion, selectivity, and yield of the reaction.

[0035] In some embodiments, the draft tube impellor may comprise at least one axial-flow impeller. In some embodiments, the draft tube impellor may comprise at least one radial-flow impeller set below the draft tube. In some embodiments, the draft tube impellor comprises a draft tube. In some embodiments, at least one axial-flow impeller is located at least partially within the draft tube. In some embodiments, the at least one axial-flow impellor is located entirely within the draft tube. In some embodiments, the draft tube is located an axial center of the reaction vessel. In some embodiments, the draft tube comprises baffles to facilitate further contact of the gas and liquid reactants.

[0036] In some embodiments, the draft tube comprises at least one cooling coil. In some embodiments, at least one cooling coil is located within the first reactor. In some embodiments,the at least one cooling coil is placed in contact with an inner surface of a reaction vessel of the reactor.

[0037] The first reactor produces an intermediate product which is then separated into at least one intermediate gaseous stream and at least one intermediate liquid stream. The intermediate liquid stream is then fed into at least one intermediate reactor.

[0038] In some embodiments, at least one intermediate reactor comprises a draft tube impellor. The draft tube impeller may comprise at least one axial-flow impeller. In some embodiments, the draft tube impellor may comprise at least one radial-flow impeller. In some embodiments, the draft tube impellor comprises a draft tube. In some embodiments, at least one axial-flow impeller is located at least partially within the draft tube. In some embodiments, the draft tube comprises baffles to facilitate further contact of the gas and liquid reactants.

[0039] In some embodiments, the draft tube comprises at least one cooling coil. In some embodiments, at least one cooling coil is located within the at least one intermediate reactor. In some embodiments, the at least one cooling coil is placed in contact with an inner surface of a reaction vessel of the at least one intermediate reactor.

[0040] Generally, as the number of intermediate reactors increases, the concentration of FSA in the final liquid stream increases.

[0041] After undergoing the desired number of intermediate reactors, an intermediate outgoing stream of liquid exits the at least one intermediate reactor. This intermediate outgoing stream of liquid is fed into a final reactor.

[0042] In some embodiments, the final reactor comprises a draft tube impellor. The draft tube impeller may comprise at least one axial-flow impeller. In some embodiments, the draft tube impellor may comprise at least one radial-flow impeller. In some embodiments, the draft tubeimpeller comprises a draft tube. In some embodiments, at least one axial-flow impeller is located at least partially within the draft tube. In some embodiments, the draft tube comprises baffles to facilitate further contact of the gas and liquid reactants.

[0043] In some embodiments, the draft tube comprises at least one cooling coil. In some embodiments, at least one cooling coil is located within the final reactor. In some embodiments, the at least one cooling coil is placed in contact with an inner surface of a reaction vessel of the final reactor.

[0044] In some embodiments, flow of the reactants and products can be facilitated by a pressure gradient across the reactors. In other words, the first reactor may be operated at a pressure greater than the operating pressure of at least one of the at least one intermediate separator and the final separator. In some embodiments, the first reactor is operated at a pressure below ambient pressure. In some embodiments, the first reactor is operated at a pressure of below about 0 psig, such as, for example, from about -1 to about 5 psig, from about -1 to about 4 psig, from about -1 to about 3 psig, from about -1 to about 2 psig, from about -0.5 to about 3 psig, from about -0.5 to about 2 psig, and from about -0.5 to about 1 psig.

[0045] When the first reactor is operated at a pressure below ambient pressure, at least one additional reactor may be operated at about 5-15” water below the pressure of the first reactor, such as, for example, from about 5” to 15” water column vacuum, from about 6” to 14” water column vacuum, from about 7” to 13” water column vacuum, from about 8” to 12” water column vacuum, and from about 9” to 11” water column vacuum.

[0046] In some embodiments, the final reactor is operated at a pressure above ambient pressure. In some embodiments, the final reactor is operated at a pressure of above about 0 psig, such as, for example, from about 0.1 to about 45 psig, from about 0.1 to about 40 psig, fromabout 0.1 to about 35 psig, from about 0.1 to about 30 psig, from about 1 to about 30 psig, from about 5 to about 30 psig, and from about 10 to about 20 psig.Process Context

[0047] In phosphate rock, typically about 3-4% fluoride can be present. In past commercial phosphate processing, when fluoride is present, it has often been seen as an undesirable contaminant. Thus, when phosphate rock is processed, particularly to phosphoric acid, the fluoride may end up as fluorosilicic acid (FSA; PhSiFe). Some phosphoric acid manufacturers have sold FSA to drinking water treatment facilities or converted it to higher value products such as silicon tetrafluoride (STF). These product lines are not growing rapidly and some have gone away in the US. Another higher value product that can be made from FSA is hydrogen fluoride (HF) which can be produced in the anhydrous state (AHF).

[0048] Another advantage of colocation of AHF facilities with phosphate rock processing (phosphoric acid manufacturing) facilities is that there is overlapping infrastructure present. For instance, AHF processes typically utilize large amounts of sulfuric acid (SA). Large phosphate rock processing (phosphoric acid manufacturing) facilities typically have sulfuric acid plants at the site. Additionally, AHF processes typically make use of high concentration SA to produce a more dilute e.g., about 70%) stream that cannot easily be stored (it can be used or disposed of). Phosphoric acid processes can typically use the dilute SA stream in their production processes.

[0049] FIG. 2 shows a block diagram of an overarching AHF process. The process contains 4 granular steps: concentration; filtration; STF production / HF generation; and AHF purification.

[0050] Typically, the FSA concentration step may not be a simple concentration operation, e.g., boiling off water to concentrate FSA, for several reasons. One can be that FSA may break down on concentration, and another can be that, when HF is formed from FSA, STF is generallyformed at the same time. The STF should typically be recovered, or else ~67% of the potential fluoride atoms would be lost. One way to recover STF is to hydrolyze it, such as to FSA and / or silica. The hydrolyzed FSA can be reincorporated into the FSA stream, thereby further concentrating it.

[0051] Because hydrolysis of STF to FSA typically also produces silica (SiOz), the concentrated FSA stream may include a combination (slurry) with silica. The silica, to the extent present, can be filtered out in the filtration section. The concentrated FSA (CFSA), which is very low in silica content, if not mostly silica-free, can be sent to the STF Production / HF Generation section. The silica, to the extent present, can be washed and can be a separate product stream or sent for disposal. The FSA wash stream, typically less dilute than “concentrated FSA,” can be sent back to the FSA concentration step for recovery.

[0052] The CFSA can be reacted in an STF reactor, e.g., with SA as a catalyst, to produce STF, which can then be recycled to the concentration section. Along with the STF, HF is typically generated. The HF can be in (or combined with) SA, and typically also water, either in liquid or gaseous form. If liquid, that combined HF / S A / water stream can be vaporized. In gaseous form, the HF / SA / water stream can be scrubbed, with a crude HF portion (see, e.g., FIG.5) typically sent to purification. The remaining SA / water may have any residual HF removed for recovery, if desired, after which it may additionally or alternatively be sent back to phosphate rock processing / phosphoric acid manufacturing process, particularly if colocated.

[0053] The purification section in FIG. 2 can typically include one or a series of distillation columns to remove heavies (e.g., water and SA), lights (e.g., STF, air), any optionally any undesired by-products. In some embodiments, such as when water content is desired to be reduced to extremely low levels (such as in the ultimate formation of AHF), an additional waterremoval step may be broadly encompassed within the purification section as well. The final, purified, AHF can be seen as a product, and is represented in FIG. 2 as being sent to storage, although it may be piped elsewhere for immediate use as an alternative to shorter- and / or longer- term storage.

[0054] FIG. 3 shows further detail of the FSA Concentration box / step from FIG. 2. In an embodiment, it is shown as a countercurrent operation in which FSA (typically at least partially in liquid phase) can be concentrated by counterflow of STF (typically at least partially in gaseous phase), represented here as the STF input to FSA Concentration from FIG. 2. Although four (4) reactors are exemplified in FIG. 3, the ordinary skilled artisan should understand that there may be more or fewer reactors present in this FSA Concentration step. Exactly at which reactor in a multi-reactor process each feed and recycle stream may enter is typically flexible, but the general idea is that FSA-based and / or predominantly liquid phase inputs can typically enter upstream in concentration on the FS A / liquid phase flow path and typically flow in the FSA / liquid phase flow direction, while STF-based and / or predominantly (solid and / or) gaseous phase inputs can typically enter downstream on the FSA / liquid phase flow path (upstream on the STF / gas phase counterflow path) and typically flow opposite the FSA / liquid phase flow direction.

[0055] The “SiF4” input shown entering Reactor 1 is meant to represent the same stream as the “STF” flow between STF Production / HF Generation box / step and FSA Concentration box / step from FIG. 2 - it can flow counter to the FSA / liquid phase flow. The feed FSA, which may be from a colocated phosphate rock processing / phosphoric acid manufacturing process, is shown as entering via Reactor 3 - it can flow in the same direction as the FSA / liquid phase flow.

[0056] At each stage (in each reactor), some STF can be converted into FSA, with the reactors being present in number and operated at conditions such that a vast majority (typically almost allthe STF) can be consumed (e.g., such that only trace amounts are “lost” to the scrubber). Water is shown as entering Reactor 4, flowing in the FSA / liquid phase flow direction opposite the STF / gas phase counterflow, with a goal of converting as much of the STF as possible into FSA. Some of the water, along with whatever FSA is converted in Reactor 4, can be sent to Reactor 3, where the feed FSA is shown to enter, and also where any optional recycle from the SiCb filtration step that may contain FSA (from the SiCh filtration box / step in FIG. 2, described as an “FSA wash stream,” but which is not specifically shown as an effluent stream) is shown as entering in FIG. 3.

[0057] A remaining portion of the water entering Reactor 4, in tandem with non-neutral pH by-products of the STF-to-SFAZ-SiOi reaction, can optionally be a side stream from Reactor 4 (and / or from any one or more of the other Reactors) and can be sent for neutralization, as desired. Additionally, though not shown, air (such as from a scrubber) may be an additional (gas phase) input to one or more of the Reactors (e.g, to Reactor 4), which air may be a recycle of the “trace SiF4-air to scrubber” (gas phase) effluent shown as exiting from Reactor 4.

[0058] From Reactor 3 to Reactor 2 to Reactor 1, as exemplified in FIG. 3, some quantity of STF can be converted into FSA, which can progressively increase the concentration of FSA. In some embodiments, the FSA concentration can increase significantly, e.g. to about 45 wt%, until CFSA, represented as an effluent exiting Reactor 1 (most downstream on the FSA / liquid phase path) can be sent to filtration.

[0059] The SiC>2 filtration step may be performed by any standard filtration method, e.g, filter press, belt filter, rotating or non-rotating pressure filters, dead end filters or the like. The basic operation for the filter can be to separate FSA from silica formed in the hydrolysis of STF to FSA, thereby increasing concentration of FSA in the process. Typically, a concentrated FSA(CFSA) stream can comprise a CFSA (typically predominantly liquid phase) portion and a cake (typically predominantly solid phase) portion. The cake portion may contain silica but may also contain some FSA “trapped” in the cake. This cake may be washed to remove any “trapped” FSA, which FSA-containing “wash” effluent can be recycled by sending it back to the FSA Concentration step. Washing of the cake can advantageously reduce losses of FSA to the cake. When utilized, washing can be batch-wise, or continuous, in a one step or multi-step counter current fashion, or the like.

[0060] The STF Production / HF Generation section (box / step) of the process (from FIG. 2) can be broken into two sub-sections, namely STF Production and HF Generation, as shown in FIG. 4. The CFSA from the SiCh Filtration step can be sent as an input stream to the STF reactor. To ensure a relatively high conversion and / or a relatively quick reaction, sulfuric acid can also advantageously be added to the STF reactor, as represented in FIG. 4 by two inputs (“Optional recycled SA streams” and “SA with HF & water”). The CFSA can be converted into HF and STF in the STF reactor, such as under relatively hot and acidic conditions. Represented in FIG. 4 as an overhead (predominantly vapor phase), an outlet of the STF reactor can comprise mostly STF (typically gas phase), but may contain some amounts of HF and / or water. The SA, HF, and water output from the STF Reactor is shown as being sent to the HF Generation subsection, which can be seen in further detail in FIG. 5.

[0061] The HF and / or water can be transformed / removed in the STF column by the addition of SA (represented in FIG. 4 as “concentrated SA” in counterflow). The (counterflowed) SA that is not consumed in the STF column can be sent to the STF reactor (shown as bottoms) as a source of SA in the STF reactor, optionally with entrained HF and / or water, if they are not separated out from the unconsumed SA.

[0062] As shown in FIG. 5, along with generating crude HF, the HF Generation sub-section also aims to achieve good recovery of HF from the SA via the HF flash tank. Indeed, an SA, HF, and water stream (output from the STF Reactor in FIG. 4) can be heated to produce a predominantly vapor-phase stream that is represented as an input to an HF Flash Tank, where pressure (and / or temperature) can be altered to separate components remaining in a vapor phase (represented as top effluent from the HF Flash Tank) from components remaining in / transforming to a condensed (e.g., liquid) phase (represented as bottom effluent from the HF Flash Tank; identified in FIG. 5 as “SA / HF / water”).

[0063] The vapor phase effluent from the HF Flash Tank can be scrubbed with SA in the HF Column to remove a considerable amount of water. The resulting (predominantly vapor phase) effluent, represented as the overhead of the HF Column, can advantageously be a crude HF stream that can be sent to purification, such as described vis-a-vis FIG. 2.

[0064] The (typically liquid phase) SA stream (represented as bottoms in FIG. 5) from the HF Flash Tank can contain HF, which optionally can be recovered, e.g., using a stripper column to remove HF, which can involve (counter)flow of air and / or steam (as shown in FIG. 5). The SA from this column can typically be dilute and can advantageously be recycled, such as to a dryer, and / or sent out to a colocated phosphate rock processing / phosphoric acid manufacturing process - FIG. 5 shows sending a portion of dilute SA to both, although needs may alternatively dictate all “dilute SA” being used by either application, to the exclusion of the other, as desired. The air stream from the stripper column can typically entrain HF and water, represented as the overhead of the stripper and effluent to the dryer in FIG. 5. In two columns (represented in FIG. 5 as a dryer and an absorber), or alternatively in a single column (not shown), the air, HF, and water can be scrubbed to recover any HF, with the resulting air (shown as the overhead effluent fromthe absorber in FIG. 5) optionally being sent to the scrubber. When two columns are used, as shown in FIG. 5, SA (bottoms from the dryer column) may be sent back to the HF Flash Tank and / or to the STF Reactor from FIG. 4 (not shown) and SA (bottoms from the absorber column) can be sent to the HF Column and / or to the STF Reactor from FIG. 4 (not shown). Although “concentrated SA” is shown as the input to the absorber in FIG. 5, using the two-column dryer / absorber option, the SA may not be concentrated (e.g., may be at one of a variety of dilutions) or may be the feed to a single column representing the dryer plus the absorber. Optionally, the temperature of any SA stream can be adjusted, as desired / needed. The “SA with HF & water optionally to STF reactor,” shown as the bottoms effluent from the HF Column in FIG. 5, represents at least one of the “Optional recycled SA streams” from FIG. 4.

[0065] With the context of FIGS. 2-5, the following linkages can be made between them and FIG. 1. The “first incoming liquid stream” from FIG. 1 can encompass the Feed FSA stream from FIG. 2, and Reactors E-3, E-2, and E-l can correspond to Reactors 3, 2, and 1, respectively from FIG. 3. The unlabeled (gaseous) input to Reactor E-3, as well as the at least one intermediate and final incoming gaseous streams from FIG. 1 can correspond to the SiF4 (gas phase counterflow) streams from FIG. 3, with the final outgoing gaseous stream from FIG. 1 corresponding to the Trace SiF4-air to scrubber stream exiting Reactor 4 in FIG. 3. Similarly, the first incoming liquid stream, the at least one intermediate liquid slurry stream, and the at least one final liquid stream from FIG. 1 can correspond to the FSA, SiO2 (liquid phase flow) streams between reactors and the Concentrated FSA, SiO2 to Filtration, respectively, from FIG. 3.Additional Embodiments

[0066] Additionally or alternatively, the following embodiments should be understood to be included within and at least partially representative of the present disclosure.

[0067] Embodiment 1. A method for concentrating fluorosilicic acid, comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product; separating the first product into at least one intermediate liquid slurry stream and at least one final outgoing gaseous stream; feeding the at least one intermediate liquid slurry stream and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream comprising fluorosilicic acid and solid silica particles, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

[0068] Embodiment 2. A method for concentrating fluorosilicic acid, comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product; separating the first product into at least one intermediate liquid stream and at least one final outgoing gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream comprising fluorosilicic acid and solid silica particles and at least one first gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greaterthan the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

[0069] Embodiment 3. A method for concentrating fluorosilicic acid through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising: reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product; separating the first product into at least one intermediate liquid stream of the at least one liquid stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

[0070] Embodiment 4. The method of embodiment 3, wherein the silicon tetrafluoride flow rate of the at least one final gaseous stream is less than the silicon tetrafluoride flow rate of the intermediate incoming gaseous stream.

[0071] Embodiment 5. The method of any one of embodiments 1 and 3-4, wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

[0072] Embodiment 6. A method for concentrating fluorosilicic acid through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising: reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product; separating the first product into at least one intermediate liquid stream of the at least one liquid stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

[0073] Embodiment 7. The method of embodiment 2 or embodiment 6, wherein each of the first reactor and the at least one additional reactor comprise the at least one draft tube.

[0074] Embodiment 8. The method of any one of embodiments 1-7, wherein the at least one draft tube comprises an axial flow impeller and / or at least one cooling coil.

[0075] Embodiment 9. The method of any one of embodiments 1-8, wherein the at least one intermediate incoming liquid stream comprises solid silica particles, and wherein the final liquid stream comprises a greater amount of solid silica particles than the amount of solid silica particles of the at least one intermediate incoming liquid stream.

[0076] Embodiment 10. The method of any one of embodiments 1-9, wherein the at least one final liquid stream comprises at least about 35 wt% of fluorosilicic acid, for example from about 37 wt% to about 45 wt% of fluorosilicic acid.

[0077] Embodiment 11. The method of any one of embodiments 1-10, wherein the first reactor is operated at or above a pressure greater than the operating pressure of the at least one additional reactor.

[0078] Embodiment 12. The method of embodiment 11 , wherein the first reactor is operated at a pressure below ambient pressure.

[0079] Embodiment 13. The method of embodiment 12, wherein the first reactor is positioned at a height greater than the at least one additional reactor and the at least one additional reactor is configured to operate at 5-15” water below the pressure of the first reactor.

[0080] Embodiment 14. The method of embodiment 11, wherein the final reactor is operated at a pressure above ambient pressure.

[0081] Embodiment 15. The reactor of any one of embodiments 1-14, wherein one or more aspects of FIGS. 2-5, as harmonized with FIG. 1, are present.ExamplesExample 1

[0082] The foregoing description has been presented for purposes of illustration. It is not exhaustive and is not limited to precise forms or embodiments disclosed. Modifications and adaptations of the embodiments will be apparent from consideration of the specification and practice of the disclosed embodiments. Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and / or alterations based on the present disclosure. It is intended that the specification and examples be considered as example only.

[0083] A stream comprising 20 wt% FSA in water enters the reactor E-3 at 50 gallons per minute (gpm). At the same time a gaseous stream enters reactor E-3 comprising STF at 213 pounds / hr. For this example, a second liquid stream, the dilute stream from washing of the filter cake, enters reactor E-3 at 94 gpm and containing 29 wt% FSA. Coolers, either internal or external, remove the heat of reaction. The resulting liquid stream has a volumetric flow rate of 144 gpm, comprising 26 wt% FSA and also 0.05 wt% SiCfi.

[0084] The 144 gpm liquid stream is then sent to reactor E-2. Additionally, there is a gaseous stream of STF containing 2,200 pounds / hr of STF sent to reactor E-2. The two streams react, in this case with an external heat exchanger pump around to remove heat, with the resulting gas stream being 213 pounds / hr STF and the resulting liquid stream being 145 gpm containing 27.5 wt% FSA with 0.5 wt% SiCE.

[0085] The 145 gpm liquid stream is sent to reactor E-l . Additionally, there is a gaseous STF stream containing 12,000 pounds per hour of STF gas sent to reactor E-l . These streams reactwithin reactor E-l, with the heat of reaction removed in a pump around loop through a heat exchanger. The results are a gaseous STF stream is with a mass flow rate of 2,200 pounds per hour, and a liquid stream with a volumetric flow rate of 151 gpm and containing 34 wt% FSA as well as 2.4 wt% SiCh.

[0086] The liquid stream with a volumetric flow rate of 151 gpm is then sent to a filter. The filter removes all or some of the SiCh from the liquid stream. The concentrated FSA, with the SiCh essentially removed, is sent to the STF reactor. The filter cake is washed with water and sent back to E-3.

[0087] The concentrated, essentially SiCh-free, stream is sent to the STF reactor with sulfuric acid. The sulfuric acid may be sent to the concentrated FSA stream directly or through an absorption or distillation column. The STF reactor decomposes the FSA into HF and STF. The STF being sent back to E-l, though it may optionally be taken through a column to remove some or essentially all the HF. The tails of the STF reactor are sent to another process to recover the HF from the sulfuric acid.

[0088] The foregoing description has been presented for purposes of illustration. It is not exhaustive and is not limited to precise forms or embodiments disclosed. Modifications and adaptations of the embodiments will be apparent from consideration of the specification and practice of the disclosed embodiments. Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and / or alterations based on the present disclosure. It is intended that the specification and examples be considered as example only.

Claims

CLAIMSWhat is claimed is:

1. A method for concentrating fluorosilicic acid, comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product; separating the first product into at least one intermediate liquid slurry stream and at least one final outgoing gaseous stream; feeding the at least one intermediate liquid slurry stream and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream comprising fluorosilicic acid and solid silica particles, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

2. The method of claim 1 , wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

3. The method of claim 2, wherein the at least one draft tube comprises an axial flow impeller.

4. The method of claim 2, wherein the at least one draft tube comprises at least one cooling coil.

5. The method of claim 1 , wherein the at least one intermediate incoming liquid stream comprises solid silica particles, and wherein the final liquid stream comprises a greater amount of solid silica particles than the amount of solid silica particles of the at least one intermediate incoming liquid stream.

6. The method of claim 1, wherein the at least one final liquid stream comprises at least about 35 wt% of fluorosilicic acid, for example from about 37 wt% to about 45 wt% of fluorosilicic acid.

7. The method of claim 1, wherein the first reactor is operated at or above a pressure greater than the operating pressure of the at least one additional reactor.

8. The method of claim 7, wherein the first reactor is operated at a pressure below ambient pressure.

9. The method of claim 8, wherein the first reactor is positioned at a height greater than the at least one additional reactor and the at least one additional reactor is configured to operate at 5- 15” water below the pressure of the first reactor.

10. The method of claim 7, wherein the final reactor is operated at a pressure above ambient pressure.

11. A method for concentrating fluorosilicic acid, comprising: reacting at least one first incoming liquid stream comprising fluorosilicic acid solution and at least one final incoming gaseous stream comprising silicon tetrafluoride in a reaction zone of a first reactor to produce a first product;separating the first product into at least one intermediate liquid stream and at least one final outgoing gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream into at least one additional reactor; reacting the fed at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream comprising fluorosilicic acid and solid silica particles and at least one first gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

12. The method of claim 11 , wherein each of the first reactor and the at least one additional reactor comprise the at least one draft tube.

13. The method of claim 12, wherein the at least one draft tube comprises an axial flow impeller.

14. The method of claim 11 , wherein the at least one draft tube comprises at least one cooling coil.

15. The method of claim 11, wherein the at least one intermediate incoming liquid stream comprises solid silica particles, and wherein the final liquid stream comprises a greater amountof solid silica particles than the amount of solid silica particles of the at least one intermediate incoming liquid stream.

16. The method of claim 11, wherein the at least one final liquid stream comprises at least about 35 wt% of fluorosilicic acid, for example from about 37 wt% to about 45 wt% of fluorosilicic acid.

17. The method of claim 11 , wherein the first reactor is operated at a pressure greater than the operating pressure of the at least one additional reactor.

18. The method of claim 17, wherein the first reactor is operated at a pressure below ambient pressure.

19. The method of claim 18, wherein the first reactor is positioned at a height greater than the at least one additional reactor and the at least one additional reactor is configured to operate at 5- 15” water below the pressure of the first reactor.

20. The method of claim 17, wherein the final reactor is operated at a pressure above ambient pressure.

21. A method for concentrating fluorosilicic acid through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising: reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product;separating the first product into at least one intermediate liquid stream of the at least one liquid stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream.

22. The method of claim 21, wherein the silicon tetrafluoride flow rate of the at least one final gaseous stream is less than the silicon tetrafluoride flow rate of the intermediate incoming gaseous stream.

23. The method of claim 21, wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

24. The method of claim 23, wherein the at least one draft tube comprises an axial flow impeller.

25. The method of claim 23, wherein the at least one draft tube comprises at least one cooling coil.

26. The method of claim 21 , wherein the at least one intermediate incoming liquid stream comprises solid silica particles, and wherein the final liquid stream comprises a greater amount of solid silica particles than the amount of solid silica particles of the at least one intermediate incoming liquid stream.

27. The method of claim 21, wherein the at least one final liquid stream comprises at least about 35 wt% of fluorosilicic acid, for example from about 37 wt% to about 45 wt% of fluorosilicic acid.

28. The method of claim 21 , wherein the first reactor is operated at a pressure greater than the operating pressure of the at least one additional reactor.

29. The method of claim 28, wherein the first reactor is operated at a pressure below ambient pressure.

30. The method of claim 29, wherein the first reactor is positioned at a height greater than the at least one additional reactor and the at least one additional reactor is configured to operate at 5- 15” water below the pressure of the first reactor.

31. The method of claim 28, wherein the final reactor is operated at a pressure above ambient pressure.

32. A method for concentrating fluorosilicic acid through a reactor system comprising at least two reactors; at least one liquid stream comprising fluorosilicic acid; and at least one gaseous stream comprising silicon tetrafluoride, wherein the at least one liquid stream and the at least one gaseous stream flow in a counter current manner, comprising:reacting at least one first incoming liquid stream of the at least one liquid stream and at least one final gaseous stream of the at least one gaseous stream at a reaction zone of a first reactor of the reactor system to produce a first product; separating the first product into at least one intermediate liquid stream of the at least one liquid stream and at least one intermediate outgoing gaseous stream of the at least one gaseous stream; feeding the at least one intermediate incoming liquid stream and an intermediate incoming gaseous stream of the at least one gaseous stream into at least one additional reactor of the reactor system; reacting the fed at least one intermediate incoming liquid stream and the intermediate incoming gaseous stream to produce at least one intermediate product; and separating the at least one intermediate product using the at least one additional reactor into at least one final liquid stream of the at least one liquid stream comprising fluorosilicic acid and at least one first gaseous stream of the at least one gaseous stream, wherein the fluorosilicic acid mass percentage in the at least one final liquid stream is greater than the fluorosilicic acid mass percentage in the at least one first incoming liquid stream, and wherein at least one of the first reactor and the at least one additional reactor comprise at least one draft tube.

33. The method of claim 32, wherein each of the first reactor and the at least one additional reactor comprise the at least one draft tube.

34. The method of claim 33, wherein the at least one draft tube comprises an axial flow impeller.

35. The method of claim 32, wherein the at least one draft tube comprises at least one cooling coil.

36. The method of claim 32, wherein the at least one intermediate incoming liquid stream comprises solid silica particles, and wherein the final liquid stream comprises a greater amount of solid silica particles than the amount of solid silica particles of the at least one intermediate incoming liquid stream.

37. The method of claim 32, wherein the at least one final liquid stream comprises at least about 35 wt% of fluorosilicic acid, for example from about 37 wt% to about 45 wt% of fluorosilicic acid.

38. The method of claim 32, wherein the first reactor is operated at a pressure greater than the operating pressure of the at least one additional reactor.

39. The method of claim 38, wherein the first reactor is operated at a pressure below ambient pressure.

40. The method of claim 39, wherein the first reactor is positioned at a height greater than the at least one additional reactor and the at least one additional reactor is configured to operate at 5- 15” water below the pressure of the first reactor.

41. The method of claim 38, wherein the final reactor is operated at a pressure above ambient pressure.

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