Minerals Refining Company

HHS Technology


Minerals Refining Company’s patented, university-developed technology, called the Hydrophobic-Hydrophilic Separation (HHS) Process, uses surface chemistry to simultaneously clean and dewater fine (-100 mesh) and ultrafine (-325 mesh) coal. The result is more tons of salable coal, reduced waste, and improved plant economics.

How it Works

  1. A feed slurry containing recoverable coal is separated from water and ash-forming minerals simultaneously via 2-liquid flotation involving a hydrophobic liquid.
  2. The two liquids are phase separated, leaving the water and ash-forming minerals in the aqueous phase, while the coal is dispersed in the hydrophobic liquid phase.
  3. The recovered coal is upgraded using a patented process.
  4. The hydrophobic liquid is recovered from the upgraded coal and used again.

Science Behind MRC’s Innovation

Slide1In Step I, a coal particle in one liquid (water) moves to another (hydrophobic liquid). The process is spontaneous with a negative free energy change. The coal particle transferred to the hydrophobic liquid will be free of surface moisture. In this transfer step, the mineral particles (such as clay) dispersed in the water will be left behind. As a result, the two-liquid flotation process removes both surface water and mineral matter simultaneously. In Step II, the coal particle is separated from the hydrophobic liquid using an appropriate solid-liquid separation process such as filtration. The residual hydrophobic liquid left on the coal surface is stripped off by vaporization/condensation, which requires energy. However, the energy requirement is approximately 14-16% of the energy required for thermal drying. Because the two-liquid flotation process is based on coal being hydrophobic and mineral matter being hydrophilic, the process is referred to as hydrophobic-hydrophilic separation (HHS).

For more information, please review the Paper that was presented by Dr. Roe-Hoan Yoon at the 2016 SME Annual Conference.


Development of HHS Technology

The HHS Process was developed at Virginia Tech by Dr. Roe-Hoan Yoon and research partner Dr. Gerald Luttrell after decades of work on fine coal cleaning and de-watering. HHS uses the concept of chemically displacing the coal from both hydrophilic mineral matter and moisture. A proprietary breakthrough discovery, made in 2010, resulted in moisture levels of -325-mesh coal dropping from +30% to single-digit values.

With the financial assistance of Evan Energy Investments, the process was further developed into a continuous, though still laboratory scale, process. Development next proceeded to the construction of a proof-of-concept (POC) unit, where large batches of waste slurry from operating preparation plants could be tested in extended runs.

3d Drawing of Pilot Plant v2PROOF-OF-CONCEPT

The proof-of-concept unit was commissioned at Virginia Tech in June of 2013. Here, Minerals Refining Company tested coal-waste slurry from a number of plants in Virginia, West Virginia, Pennsylvania and Kentucky. The HHS process consistently produced a salable coal product with ash content of 3% to 6% by weight and single-digit moisture values.


With a proven technology in hand, MRC entered into a commercial contract with the one of the largest U.S. coal companies to install a 1 clean-ton per hour Pilot Plant at an operation in Southwest Virginia. The plant became operational in late 2015 and completed testing in 2017.  It successfully upgraded a split of the <40 µm (<325 mesh) deslime-cyclone overflow and recovered the coal as a high-quality product.  The 5%-solids slurry feed averaged 58% ash, while the final product contained 4-1/2% ash and 5-to-9% moisture.  The moisture is controllable while the ash is a function of the seam liberation characteristics.  The ash achieved can be compared to the overall quality produced by plant, which is 6-1/2%.

Commercial Plants

On the strength of the pilot plant results, MRC is currently designing the first commercial plant, with construction scheduled to start before the end of 2018.  The first plant will be located in the coalfields of Central Appalachia, with an expected output of 20 tons per hour of clean coal.


Safety is the highest priority for MRC. Consistent with the safety measures taken in the design and construction of MRC’s Pilot Plant, all commercial HHS plants will be equipped with numerous safety features. Most notably, the entire HHS Process is performed under a nitrogen-inerting atmosphere.