Systems and methods to treat flue gas desulfurization and metal-bearing waste streams to recover value-added materials
Disclosed herein are systems and methods from processing flue gas desulfurization (FGD) gypsum feedstock and ash feedstocks, either separately or together. FGD gypsum conversion comprises reacting FGD gypsum (e.g. calcium sulfate) feedstock, in either batch or continuous mode, with ammonium carbonate reagent to produce commercial products wherein the commercial products comprise ammonium sulfate and calcium carbonate. Ash conversion comprises a leach process followed by a precipitation process to selectively precipitate components at predetermined pHs resulting in metal hydroxides which may be optionally converted to oxides or carbonates. The processes may be controlled by use of one or more processors.
1 . A method for processing a waste stream, the method comprising:
configuring a processor to operate a process comprising:
loading a first powder feedstock into a first reactor, wherein the first powder feedstock comprises a calcium sulfate component;
introducing an ammonium carbonate reagent to the first reactor to produce ammonium sulfate and calcium carbonate in a reaction slurry;
pumping the reaction slurry to a second reactor when a reaction to produce ammonium sulfate and calcium carbonate is complete thereby forming a reacted slurry;
filtering the reacted slurry resulting in a calcium carbonate residue and ammonium sulfate filtrate liquor;
loading a second powder feedstock into a third reactor, wherein the second powder feedstock comprises a metal-bearing component, a silica component, and an aluminosilicate component;
leaching the second powder feedstock by at least one of contacting, passing, and percolating an acid and hydrogen peroxide through the second powder feedstock and collecting a metal-bearing leachate formed in the third reactor, wherein after collecting the metal bearing leachate, the third reactor comprises dried solids comprising silicates;
responsive to collecting the metal-bearing leachate, adjusting a pH value of the metal-bearing leachate to a first predetermined pH value to precipitate a first component from the metal-bearing leachate, wherein the first predetermined pH value is 4, and wherein the first component comprises iron and aluminum;
responsive to precipitating the first component, separating by filtration the first component, and collecting a first filtrate in a fourth reactor; and
responsive to collecting the first filtrate, adjusting the first filtrate to a second predetermined pH value to precipitate a second component from the first filtrate, separating by filtration the second component to result in a second filtrate, and collecting the second filtrate in a fifth reactor.
2 . The method of claim 1 , wherein the processor uses the predetermined pH values to separate the components based on predetermined logic.
3 . The method of claim 1 , wherein leaching the second powder feedstock is performed in one or more stages.
4 . The method of claim 1 , wherein the acid comprises sulfuric acid, nitric acid, hydrochloric acid, or any combination thereof.
5 . The method of claim 1 , further comprising adjusting the first filtrate to the second predetermined pH value using a base component that is at least one of calcium hydroxide, sodium hydroxide, potassium hydroxide, and ammonium hydroxide.
6 . The method of claim 1 , wherein the first component and the second component are hydroxides of at least one of iron, aluminum, and a mischmetal, wherein the mischmetal is a mixed metal alloy of rare-earth elements.
7 . The method of claim 1 , wherein the first component or the second component includes a mischmetal, wherein the mischmetal is a mixed metal alloy of rare-earth elements and wherein the mischmetal is at least one of a cerium mischmetal and a rare-earth mischmetal, wherein the rare-earth mischmetal comprises at least one of cerium, lanthanum, scandium, and neodymium.
8 . The method of claim 1 , wherein the first component further comprises scandium or uranium.
9 . The method of claim 1 , wherein the process further comprises calcining the first component.
10 . The method of claim 9 , wherein the first component comprises iron in the form of ferric hydroxide, and wherein calcining the first component results in the formation of a ferric oxide product.
11 . The method of claim 1 , wherein the pH of the metal-bearing leachate is about 1.5.