Phosphoric Acid Sector

There are a number of K-Tech process applications that have a range of applicability to various industrial sectors. Examples of specific process opportunities that can be developed within the wet-process phosphoric acid industry, utilizing the core K-Technologies expertise, include, but are not limited to, the following:

Uranium Extraction
from Phosphoric Acid

K-Technologies, Inc. has extensive in-house expertise relative to the recovery of uranium from phosphoric-acid operations (U3O8 from P2O5). K-Tech personnel were instrumental in the development and commercialization of the so-called “Second Generation” solvent extraction technology that was implemented in the mid-late 1970’s. This type of technology became the mainstay of the U3O8 from P2O5 industry for the 1970’s-90’s
time period.

As a result of various economic pressures in the 1990’s, these 2nd Generation systems were shut down and the industry remained somewhat dormant for a period of years. Continued expansion of the nuclear power industry, and the associated long-term demands for U3O8 have renewed interest in the recovery of U3O8 from “non-conventional” sources, such as phosphoric acid. Uranium demand is expected to continually outstrip supply as new deposits become more difficult and costly to develop and secondary sources from government stockpiles decline.

While having in-house expertise available relative to the solvent extraction methodologies, K-Tech has continued its efforts to develop advanced (Generation 3) recovery techniques. These systems do not rely on solvent extraction approaches, but rather are based on the application of continuous non-solvent extraction techniques, e.g. modified solid sorbent systems. They result in a more simplified process and plant footprint; reduced capital and operating costs; and enhanced safety aspects. These advanced techniques utilize K-Tech’s proprietary continuous processing technology to allow for the application of the non-solvent systems.

As a result of these efforts over the past several years, K-Tech has demonstrated the effectiveness of the approach at both the bench-scale and pilot plant level. The process approach utilizes a 2-stage system where the U3O8 is removed from the primary phos-acid stream and recovered as a concentrated intermediate stream. The concentrated (U) stream is further treated in a smaller secondary system to produce a final purified U-containing solution which is then processed in a standard refining system to produce high purity natural uranium oxide (U3O8) as a solid product.

It should be noted that this natural U3O8 product is identical, from a handling and safety standpoint, to those materials produced in “conventional” uranium mining and milling operations currently in operation in some 16 countries around the world. Natural uranium is the starting raw material in the nuclear fuel cycle, and must be upgraded in two additional steps at other highly regulated licensed facilities in order to make fuel suitable for nuclear power plants. These steps involve first converting the U3O8 to UF6 gas, and then enriching the fissionable U-235 content from 0.7% to 3.5% to 5%.

Detailed economic analyses indicate that significant capital and operating cost savings are potentially achievable with the 3rd Generation K-Tech U3O8 from P2O5 recovery processes. These savings can range from 25% to 35% depending on the size of the facility and other site specific conditions. More detailed information can be found in papers we have presented at several international conferences.

Further, recent work indicates that the K-Tech 3rd Generation technology may be applicable to the recovery of U3O8 from P2O5 in more concentrated phos-acid streams, such as those originating from the Hemi-Hydrate P2O5 processes. This finding significantly increases the hemi-hydrate producers’ opportunity for value-add from this source.

K-Tech has the ability to evaluate Client samples to determine the applicability of the approaches to a specific phos-acid feedstock and can provide Clients with important information of the potential attractiveness of U3O8 recovery to its operations. These indications can be developed at reasonable costs so as to allow for insightful and informed decisions to be made by the Client with minimal front-end risks.

Rare Earths Recovery
from Phosphoric Acid

Wet process phosphoric acid represents a significant “non-conventional” rare earth (RE) source, and K-Tech has technology for the recovery of RE from this source. More importantly, K-Tech also has technology for the subsequent purification of the recovered RE to produce individual rare earth products such as europium oxide, terbium oxide, etc. K-Tech personnel have been working with RE recovery and separations from a variety of process streams since the early 1980’s and have developed recovery concepts for a number of “non-conventional” sources, including phos-acid.

Over the past several years the RE markets and supply chain have seen some rather dramatic movements, and the market now realizes that RE from other sources, both from a feedstock and geographical standpoint, are needed. As such, there has been a significant increase in RE sourcing assessments and evaluation of alternate feedstock sources.

It is well known that many phosphate rock sources contain some level of RE, but the concentrations tend to be low, i.e. in the parts/million to hundreds of parts/million. It is also known that during the rock digestion process, the majority of the RE is not dissolved, but remains in the phosphogypsum waste. However, some percentage of available RE does dissolve into the phosphoric acid and this is where K-Tech has focused its recovery efforts.

An obvious advantage of the phos-acid source is that the bulk of the front-end work, i.e. getting the RE out of the ground and into solution, has already been done as a result of the phos-acid process requirements, i.e. mining, beneficiation, grinding, dissolution, liquid/solids separation, etc. Even considering the RE losses to the phosphogypsum, this provides potential economic attractiveness when compared to conventional ore sources. Obviously, the key is to have an economical method to recover and purify the relative low concentrations of the rare earths from the phos-acid media.

K-Tech has technology that can be applied to this task. The techniques employed allow for removal of the low concentrations of RE from the phos-acid, using non-solvent extraction methods, with the subsequent production of a low volume intermediate stream that contains a significantly higher concentration of rare earths than was present in the starting phos-acid.

This intermediate can be further processed to produce a marketable mixed RE product. Since the rare earths in phos-acid tend to be relatively higher in the more desirable mids and heavies RE fractions, this mixed intermediate should have an inherently higher value in the marketplace when compared with “conventional” mixed salt concentrates, e.g. RE-carbonates from traditional sources.

Once the RE have been recovered as an intermediate fraction, the next step in major value-add potential is to have a process that can separate the individual RE components from one another. From a chemical separation standpoint, this represents the major process challenge, as the individual RE species all behave in much the same manner. Therefore, techniques such as fractional crystallization, specific precipitations, and the like are generally not applicable. It is to this end that more efficient separation techniques must be applied. K-Tech has developed technology that allows for the continuous processing of the intermediate rare earth-containing solution to separate the individual RE from each other. Thus, purified materials such as europium oxide, terbium oxide, yttrium oxide, etc. can be produced using K-Tech’s processes.

With the K-Tech process approach, the recovery of RE from phos-acid sources as a mixed intermediate product may represent an attractive option to the phos-acid producer to add value and enhance

overall plant economics. Additional value-add can be achieved by further processing the intermediate solution to produce individual purified RE products.

The economics associated with the recovery of rare earths, (and possibly combined RE/uranium) will vary from site to site. Specific rock and attendant phos-acid sources will yield different results. However, based on several different phos-acid sources that have been assessed by K-Tech, the projected capital and operating costs associated with rare earths recovery are typically much less than those associated with the “conventional” processing operations. This becomes especially attractive in the combined case of simultaneous RE and U recovery (for which K-Tech has developed processing techniques).

Furthermore, and depending on the degree that the RE are recovered and separated, rare earths may offer a value-add that is potentially higher than uranium recovery from phos-acid. Even better, the simultaneous recovery of both rare earths and uranium could provide the P2O5 producer with exceptional value-add economics and diversification options.

Minor Element Reduction
in Phosphoric Acid

In the production of wet-process acid, there are a number of impurities that are dissolved into the phos-acid stream, along with the P2O5 component, as a result of the phosphate rock digestion with sulfuric acid. While many of these impurities have little effect on the downstream processing of the acid to produce various products, some of these impurities can have detrimental impacts on the ability of the acid to produce specification-grade products such as merchant-grade acid (MGA) or diammonium phosphate (DAP) fertilizer.

In general, the key items of concern in the phos-acid are the so-called “minor elements (ME)” that consist of iron (expressed as Fe2O3); aluminum (expressed as Al2O3); and magnesium (expressed as MgO). To provide an indication of an acid’s ability to produce specification fertilizer products, particularly DAP, the ratio of the total minor elements (Fe2O3+Al2O3+MgO) to the total P2O5 (ME/P2O5) in the filter acid is used. In general, an MER of less than about 0.08 is desirable.

Unfortunately, as phosphate rock reserve quality has gradually decreased over the years, and newer reserves have been identified with higher ME levels, there is a need for a technique that can economically reduce the MER in a given phos-acid stream with minimized P2O5 losses and acid strength dilution. While various techniques have been evaluated in the past, in most cases their application to higher MER acids results in excessive P2O5 losses, or other adverse effects, such as production of large amounts of low-grade fertilizer by-products which are unsalable.

To this end K-Tech has developed technology for the reduction of the MER in wet-process acid. This process is based on the application of a specialized continuous sorbent contacting system where a target portion of the ME’s are removed from the acid, then recovered as a separate concentrated stream of soluble ME materials (non-P2O5 compounds). The recovered ME’s can be disposed of directly to the facility’s gypsum stack system, or separately treated to produce a ME-precipitate that can be disposed of.

The treated phos-acid is returned to the P2O5 plant for further downstream processing. P2O5 losses and dilution are minimal and there is no need to handle quantities of low-grade ME-phosphates, as is the case with some of the previous approaches.

Alternatively, depending the nature of the ME species ratio, there is the opportunity to recover the removed ME components as one or more saleable co-product(s). For example, if a phos-acid contains excessive levels of magnesium, then this component can be removed from the acid and converted to a magnesium sulfate solution or dry product. Since magnesium sulfate has secondary fertilizer nutrient value in the form of soluble magnesium and sulfur, and also as an animal feed ingredient, the “impurity” in the acid becomes a co-product opportunity.

While the bulk of the work with the MER reduction technique has been conducted with Di-Hydrate filter acid (25-28% P2O5), further test work has indicated that it is applicable to higher strength P2O5 solutions, i.e. in excess of 50% P2O5. This would allow for a smaller stream of acid to be treated if there was a situation where only a portion of the P2O5 required MER reduction, e.g. preparation of super-phosphoric acid from high MgO concentrated acid. It would also allow for the treatment of higher MER phos-acids that are produced in the Hemi-Hydrate or Hemi-Dihydrate processes.

A general discussion relative to the K-Tech MER reduction process is contained in an accompanying paper that was delivered at an international symposium.

As in the case of the U recovery process, K-Tech can readily assess the potential applicability of the MER reduction process to a given acid source at the Phase 0 or limited laboratory testing level. This approach allows for a cost-effective determination of the potential attractiveness of this approach to a Client’s specific acid.

Fluoride and Silica Recovery from Phos-Acid Vapors or Pond Waters

As a result of a number of years of participation by K-Tech personnel in process evaluations, assessments, pilot plant, and demonstration programs, specialized technology has been developed that can be applied to the recovery of fluoride and silica materials from various phos-acid plant streams. Specifically, recovery of fluoride and silica materials from phos-acid vapors originating from the phos-acid digestion and concentration operations themselves can be carried out using one of several methodologies.

For example, if the P2O5 operation already has hydrofluosilicic acid (H2SiF6) recovery, then this intermediate stream can be processed to produce up-graded products. If there is not an existing recovery operation then the barometric cooling system can be modified to allow for fluoride/silica recovery as well as allow for improved cooling techniques to minimize the amount and area of fluoride-silica containing cooling pond waters at
the facility.

A more attactive opportunity for the phos-acid producer may be the recovery of fluoride and silica from recirculating cooling/gypsum pond waters. This technique has been demonstrated via the operation of a large-scale pilot operation a number of years ago and allows for a total disconnect of the F/Si operation from the phos-acid plant. This ensures that the F/Si operation has zero impact on the phos-acid operation. Assuming that the gypsum and cooling ponds are interconnected, the recovery of F/Si from pond water, can take advantage of the soluble fluoride and silica components that have been “stacked” in the gypsum pile, thus providing for a large starting “inventory” of F and Si. Recovery of F/Si from recycled pond water also allows for the potential recovery of contained P2O5, which would be handled separately. In the cases of revised barometric condenser operation and/or recovery from recirculated pond waters, the F/Si components are removed from the solution stream, using advanced continuous ion exchange techniques. They are then recovered as a concentrated fluosilicate solution. This solution is then processed to separate the fluoride species from the silica components.

In the past, fluosilicic acid materials have been processed to reject the silica “impurity” and allow for the production of fluoride salts. This represented an economic “short-fall”: in the process. By utilization of advanced processing techniques, the separation of the silica material from the fluoride component can now be accomplished to produce high quality, precipitated-grade silica products which have a multitude of industrial and food grade uses and are marketed as premium products.

As the markets for precipitated silica products are fairly large, recovery of silica from a phos-acid operation is not likely to substantially impact market pricing. In addition, this recovery methodology can yield silica products at significantly lower capital and operating costs compared with the more conventional precipitated silica production techniques.