METHOD AND APPARATUS FOR REMOVING ARSENIC FROM AN ARSENIC BEARING MATERIAL
A method and apparatus for removing arsenic from an arsenic-bearing material. The method includes the steps of contracting an arsenic-bearing material with an arsenic leaching agent to form an arsenic-containing solution and arsenic-depleted solids. The leaching agent can be an inorganic salt, an inorganic acid, an organic acid, and/or an alkaline agent. The arsenic-depleted solids are separated from the arsenic-containing solution, which is contacted with a fixing agent to produce an arsenic-depleted solution and an arsenic-laden fixing agent. The fixing agent comprises a rare earth-containing compound that can include cerium, lanthanum, or praseodymium. The fixing agent is then separated from the arsenic-depleted solution. A recoverable metal in the arsenic-depleted solids, arsenic-containing solution or arsenic-depleted solution can be separated and recovered. Recoverable metals can include metal from Group IA, Group IIA, Group VIII and the transition metals.
1 . A method for removing arsenic from an arsenic-bearing material, the method comprising the steps of:
contacting an arsenic-bearing material with an arsenic leaching agent to form an arsenic-containing solution and arsenic-depleted solids;
separating the arsenic-depleted solids from the arsenic-containing solution;
contacting the arsenic-containing solution with a fixing agent under conditions in which at least a portion of the arsenic is fixed by the fixing agent to yield an arsenic-depleted solution and an arsenic-laden fixing agent, the fixing agent comprising a rare earth-containing compound; and
separating the arsenic-laden fixing agent from the arsenic-depleted solution.
2 . The method of claim 1 , wherein one or more of the arsenic-containing solution, the arsenic-depleted solids, and the arsenic-depleted solution comprises a recoverable metal.
3 . The method of claim 2 , further comprising the step of precipitating the recoverable metal from one or more of the arsenic-containing solution and the arsenic-depleted solution.
4 . The method of claim 2 , further comprises the step of electrolyzing one or more of the arsenic-containing solution and the arsenic-depleted solution to separate the recoverable metal.
5 . The method of claim 2 , further comprising adding the arsenic-depleted solids to a feedstock in a metal refining process to separate the recoverable metal.
6 . The method of claim 1 , wherein the arsenic leaching agent comprises one or more of an inorganic salt, an inorganic acid, an organic acid, and an alkaline agent.
7 . The method of claim 6 , wherein the alkaline agent comprises sodium hydroxide.
8 . The method of claim 1 , wherein the recoverable metal comprises a metal from Group IA, Group IIA, Group VIII and the transition metals.
9 . The method of claim 1 , wherein the arsenic-containing solution has a pH of more than about 7 when the arsenic-containing solution is contacted with the fixing agent.
10 . The method of claim 9 , wherein the arsenic-containing solution has a pH of more than about 9 when the arsenic-containing solution is contacted with the fixing agent.
11 . The method of claim 10 , wherein the arsenic-containing solution has a pH of more than about 10 when the arsenic-containing solution is contacted with the fixing agent.
12 . The method of claim 1 , wherein the arsenic-containing solution has a pH of less than about 7 when the arsenic-containing solution is contacted with the fixing agent.
13 . The method of claim 12 , wherein the arsenic-containing solution has a pH of less than about 4 when the arsenic-containing solution is contacted with the fixing agent.
14 . The method of claim 13 , wherein the arsenic-containing solution has a pH of less than about 3 when the arsenic-containing solution is contacted with the fixing agent.
15 . The method of claim 1 , wherein the arsenic-containing solution comprises at least about 1000 ppm sulfate when the arsenic-containing solution is contacted with the fixing agent.
16 . The method of claim 1 , wherein the recoverable metal is in solution and the fixing agent comprises an insoluble compound that does not react with the recoverable metal to form an insoluble product.
17 . The method of claim 1 , wherein the rare earth-containing compound comprises one or more of cerium, lanthanum, or praseodymium.
18 . The method of claim 17 , wherein the rare earth-containing compound comprises a cerium-containing compound derived from thermal decomposition of a cerium carbonate.
19 . The method of claim 17 , wherein the rare earth-containing compound comprises cerium dioxide.
20 . The method of claim 1 , wherein the arsenic-depleted solution comprises less than about 20 ppb arsenic.
21 . An apparatus for removing arsenic from an arsenic-bearing material, the apparatus comprising:
a leaching unit for contacting the arsenic-bearing material with an arsenic leaching agent under conditions such that at least a portion of the arsenic is extracted to form an arsenic-containing solution and arsenic-depleted solids;
a separator for separating the arsenic-containing solution from the arsenic-depleted solids;
an arsenic fixing unit operably connected to the leaching unit to receive the arsenic-containing solution, the arsenic fixing unit comprising a contact zone having a fixing agent comprising a rare earth-containing compound for contacting the arsenic-containing solution and fixing at least a portion of the arsenic to yield an arsenic-depleted solution and an arsenic-laden fixing agent; and
a separator for separating the arsenic-laden fixing agent from the arsenic-depleted solution.
22 . The apparatus of claim 21 , further comprising a metal recovery unit operably connected at least one of the leaching unit and the arsenic fixing unit for separating a recoverable metal from one or more of the arsenic-depleted solids, the arsenic-containing solution, and the arsenic-depleted solution.
23 . The apparatus of claim 22 , wherein the metal recovery unit comprises an electrolyzer.
24 . The apparatus of claim 22 , wherein the metal recovery unit comprises a precipitation vessel.
25 . The apparatus of claim 22 , wherein the recoverable metal is in solution in the arsenic-containing solution and the fixing agent comprises an insoluble compound that does not react with the recoverable metal to form an insoluble product.
26 . The apparatus of claim 21 , wherein the rare earth-containing compound comprises one or more of cerium, lanthanum, or praseodymium.
27 . The apparatus of claim 26 , wherein the rare earth-containing compound comprises a cerium-containing compound derived from cerium carbonate.
28 . The apparatus of claim 26 , wherein the rare earth-containing compound comprises cerium dioxide.
29 . The apparatus of claim 21 , further comprising a filtration unit connected to the arsenic fixing unit for receiving the arsenic-laden fixing agent and producing a filtrate.
30 . The apparatus of claim 29 , wherein the filtration unit is in fluid communication with an inlet of the arsenic fixing unit for recycling the filtrate to the arsenic fixing unit.
31 . The apparatus of claim 21 , wherein the contact zone is disposed within a column.
32 . The apparatus of claim 21 , further comprising a second arsenic fixing unit comprising:
a contact zone having a fixing agent comprising a rare earth-containing compound for contacting the process stream and fixing at least a portion of the arsenic to yield an arsenic-depleted stream comprising the recoverable metal and an arsenic-laden fixing agent; and
a separator for separating the arsenic-laden fixing agent from the arsenic-depleted solution.
33 . The apparatus of claim 32 , further comprising a manifold in fluid communication with an inlet of each of the arsenic fixing units for selectively controlling a flow of the process stream to each of the arsenic fixing units.
34 . The apparatus of claim 32 , further comprising a manifold in fluid communication with an inlet of each of the arsenic fixing units for selectively controlling a flow of a sluce stream to each of the arsenic fixing units.
35 . The apparatus of claim 32 , further comprising a manifold in fluid communication with an inlet of each of the arsenic fixing units for selective controlling a flow of the fixing agent to each of the arsenic fixing units.