Amine-aldehyde resins and uses thereof in separation processes

A method for purifying a coal ore, comprising:

• a. providing a coal ore comprising coal and one or more soluble or insoluble impurities;
• b. prior to or during a size or a density classification operation, contacting an aqueous slurry of the coal ore with an amine-aldehyde resin, and
• c. separating the purified coal from the aqueous slurry;
• wherein the purified coal has, relative to the coal ore, a reduced amount of mercury, nitrogen, sulfur, silicon, ash, or pyrite, as measured on a volatile free weight basis;
• and
• wherein the amine-aldehyde resin comprises a urea-formaldehyde resin prepared by:
• mixing formaldehyde, urea, triethanolamine and optionally ammonia reactants at an alkaline pH, heating the mixture to an elevated temperature for a time sufficient to obtain complete metholylation of the urea, the reactants being present in an amount of about 1.50 to 4.0 moles of formaldehyde, about 0.001 to 0.1 mole of triethanolamine, and about 0.0 to 0.5 mole ammonia, per mole of urea;
• and
• adding acid to lower the pH to within the range of about 4.9 to about 5.2 and adding urea until the molar formaldehyde to urea ratio is within the range of about 1.5:1 to about 2.5:1 and reacting for a time sufficient to reduce free formaldehyde to less than 2%.