BACKGROUND AND SUMMARY OF THE INVENTION

This application claims benefit of provisional patent application Ser. Nos. 62/994,214, filed Mar. 24, 2020, and 63/047,830, filed Jul. 2, 2020.

The invention concerns recovery of rare earth elements and creating a new source of rare earth minerals. In particular, the invention involves recovery of REEs from wastewater, particularly acid mine water, or leachate from coal ash piles or coal refuse or gob piles, or water from pools in deep mines or from coal ash ponds or from other mining operations, using Sulfur Modified Iron (SMI). The invention also encompasses removal of contaminants from water using SMI, wherein REEs are removed as a byproduct.

Sulfur Modified Iron has been used for some years to remove metal contaminants from water. Sometimes the contaminated water is in groundwater, sometimes in drainage ponds, sometimes in leachate, sometimes in industrial process water. The contaminants have included selenium, nitrates, chromium, cadmium and arsenic and compounds of these substances. The contaminant metals are adsorbed and/or absorbed (chemisorbed) by the SMI and fixed to the SMI. SMI is effective in removing small (low level) concentrations of these metal contaminants from water, often to a level below detectable limits. Normally the SMI with contaminants fixed to the particles is disposed of safely without risk that the contaminants will be released back into the environment.

Rare earth metals if present in the water are also adsorbed/absorbed (chemisorbed) to the SMI and fix (bind) to the SMI particles. Rare earth metals found in low concentrations in water include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu) gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y). The water may have picked up the rare earth metals by leaching through rock at a mining site or at other locations, such as coal ash piles, coal ash ponds, gob piles or refuse piles from deep mining.

The REEs are identified as rare because it is unusual to find them in large concentrations; they are not actually rare. Conventional rare-earth recovery methods require an expensive, difficult and messy extraction process that generates large volumes of contaminated waste. The conventional mining and extraction processes require mining ore from mineral deposits in rock, which is crushed into a powder, dissolved in powerful chemical solutions and filtered. The process is repeated multiple times to retrieve rare earth oxides. Additional processing and refining separates the oxides from their tight bonds and further groups them into light rare earths and heavy rare earths.

In usable form, these elements are necessary components of many modern technologies. Many of them are used in cellular phones, computers, televisions, magnets, batteries, catalytic converters, defense applications and many more segments of modern society.

As an example, acid mine drainage from abandoned mines, or active mines, is one of the biggest industrial pollution sources in Appalachian streams. SMI has been used effectively to remove contaminants from these sources. While reducing unwanted contaminants, the SMI also adsorbs/absorbs and fixes to the SMI rare earth metals that may be present in this water. The SMI concentrates these rare earth metals while cleaning millions of gallons of mine drainage, so that the rare earth metals can be cost-effectively extracted. Coal and the water coming from coal mines can contain all 17 of the rare earth elements, with a substantial amount of the heavy rare earths that are particularly valuable.

Pursuant to the invention, water expected to contain rare earth metals is collected at a site, illustrated herein with a coal mining site, either a surface mine or a deep mine. Such sites will also typically contain selenium, in various oxidated compounds, as discussed in the applicant's U.S. Pat. Nos. 9,272,934, 9,427,706, 9,878,922 and 10,059,613.

In one aspect of the process of the invention, the REE-containing runoff water at a surface coal mining site is caught in detention ponds. In the above-cited patents remediation of the pond water to remove selenate down to permissible levels for discharge to lakes and streams was performed by treatment with Sulfur-Modified Iron (SMI) in an upflow reactor vessel. The SMI will also contain REEs, which will be a by-product of essentially the same process. In some instances the REEs can be the primary product of the SMI process.

After a prefiltering step to remove suspended and colloidal solids, the runoff or pond water is pH-adjusted as needed and pumped through the SMI reactor in upward flow, for a specified detention time in the SMI. The treated water can then be run through an oxidation tank and filtered to remove dissolved iron that is a residual from the SMI process. The process preferably is run in continuous flow.

After a period in which the SMI becomes essentially saturated and less effective and no longer removes appreciable amounts of the contaminant and/or REEs, the spent SMI is removed and processed to separate out rare earth metals, which can be done using existing extracting technologies.

As in the previous patents, the system preferably includes provision for “fluffing” the SMI medium periodically, to expand the bed of SMI with a rapid flow of water through the medium. Not a backflush, this fluffing opens up the spaces between SMI particles, reversing compacting that has occurred, and refreshes the active surfaces to extend the life of the bed. This can be done once or more per day, for about ten to twenty minutes, at, for example, about ten times normal (service) flow rate. Fluff flow is in the same upflow direction as normal service flow. This fluffing cycle is useful in any SMI reactor column removing metals or other substances from water, not limited to coal mine runoff. As an alternative the SMI medium can be as a continuous moving medium, as discussed further below.

The process of the invention encompasses water from deep coal mines as well as surface mines. Acid mine drainage water can be extracted from deep mine pools far beneath the surface, where reclamation has covered all traces of the mine at the surface. In addition, the process can be applied to gob piles or refuse piles from deep coal mines, some of which include millions of cubic yards of rocks, clay and other refuse separated from coal brought out of the mines, and these refuse piles contain REEs.

It is an object of the invention to provide a process and system which effectively and efficiently extract REEs from water, particularly acidic water at, for example, a coal mining site. This can be as a byproduct of a process to remediate contaminants from the water or from refuse or ash piles, or as a primary product. Other objects and advantages of the invention will be apparent from the following description of preferred embodiments, considered along with the accompanying drawings.

