Aqueous Biphase Extraction for Processing of Fine Coal

Abstract

EXECUTIVE SUMMARYThe objective of this research project is to develop an aqueous biphase extraction process for the treatment of fine coals. Aqueous biphase extraction is an advanced separation technology that relies on the ability of an aqueous system consisting of a water-soluble polymer and another component, e.g., another polymer, an inorganic salt, or a nonionic surfactant, to separate into two immiscible aqueous phases. The principle behind the partition of solid particles in aqueous biphase systems is the physicochemical interaction between the solid surface and the surrounding liquid solution. In order to remove sulfur and mineral matter from fine coal with aqueous biphasic extraction, it is necessary to know the partitioning behavior of coal, as well as the inorganic mineral components. Therefore, in this research emphasis was placed on the partitioning behavior of fine coal particles as well as model fine inorganic particles in aqueous biphase systems.In the polyethylene glycol (PEG)/salt/H 2 O system, it was found that pyrite partition was highly dependent upon pH conditions: at high pH the particles preferred the salt-rich (bottom) phase, while they moved to the polymer-rich (top) phase at low pH. This behavior is attributable to the different surface oxidation products associated with the pH variations: formation of FeOOH in alkaline solution, and a hydrophobic iron-deficient product (Fe 1-x S 2 ) in acidic environment. The partitioning behavior of oxide particles (e.g., Al 2 O 3 , Fe 2 O 3 , SiO 2 , TiO 2 ) in the PEG/Na 2 SO 4 /H 2 O system indicated that, in the absence of polymer-solid interaction, the surface hydrophilic/hydrophobic properties determined solid partition; otherwise, the specific polymer-solid interaction dominated the distribution of the solid particles.Aside from the polymer/salt aqueous biphase systems, the partitioning behavior of hematite and silica was also investigated in polymer/polymer (PEG/dextran) and polymer/nonionic surfactant (Triton X-100 (TX100)/dextran) systems. In these systems interaction between the phase components and the solid surface played an important role in determining the solids distribution. For both biphase systems, hematite stayed in the bottom dextran-rich phase, which was attributable to the strong interaction between dextran and ferric oxide. However, the partitioning behavior of silica was found to be pHdependent. At low pH the particles preferred the top phase; with increase in pH, the solids gradually moved to the interface, then to the bottom phase and they transferred back to the top phase again at very high pH. The results were attributed to the competition between dextran/SiO 2 and TX100/SiO 2 or dextran/SiO 2 and PEG/SiO 2 interactions.Surfactant addition also offers an important way to change the surface chemistry of a solid. In the PEG/salt/H 2 O system, it is found that only surfactants adsorbed chemically on the solid surfaces had a significant influence on solid distribution, e.g., xanthate/pyrite and oleate/hematite. In contrast, i...

Aqueous Biphase Extraction for Processing of Fine Coal

“…The partitioning behavior of many inorganic particles in aqueous biphase systems has been investigated in our laboratory (18)(19)(20). As in conventional liquid-liquid extraction (21)(22)(23), the partition of particles in aqueous biphase systems is dependent upon the physicochemical interaction between the solid surface and the liquid solution, rather than the bulk properties of the solid or solution such as density.…”

“…In previous paper, the partitioning behavior of silica in the PEG/Na 2 SO 4 system (19) has been studied. In this system, the particles prefer the top PEG-rich phase under all pH values, which is attributable to the specific polymer-solid interaction through hydrogen bonding between the surface silanol groups and oxygen atoms in the polymer chains.…”

“…In this system, the particles prefer the top PEG-rich phase under all pH values, which is attributable to the specific polymer-solid interaction through hydrogen bonding between the surface silanol groups and oxygen atoms in the polymer chains. No information has been found in the literature about the partition of silica in the polymer/polymer or polymer surfactant aqueous biphase systems (8)(9)(10)(11)(12)(13)(14)(18)(19)(20). For comparison with our previous studies (19), this work will investigate the partition of silica in the Dex/TX100 and PEG/Dex system.…”

“…No information has been found in the literature about the partition of silica in the polymer/polymer or polymer surfactant aqueous biphase systems (8)(9)(10)(11)(12)(13)(14)(18)(19)(20). For comparison with our previous studies (19), this work will investigate the partition of silica in the Dex/TX100 and PEG/Dex system. In the polymer/nonionic surfactant systems, additions of ionic surfactant successfully modify the distribution of proteins (24)(25)(26).…”