METHOD AND APPARATUS FOR REMOVING ARSENIC FROM A SOLUTION
A method and apparatus for separating arsenic from an aqueous solution containing arsenic. The method includes the steps of contacting an arsenic-containing solution with a first portion of fixing agent to remove at least a portion of the arsenic. An arsenic-laden fixing agent is separated from the solution and the partially depleted solution is contacted with a second portion of fixing agent. The fixing agent can include a high surface area insoluble compound containing one or more of cerium, lanthanum, or praseodymium. Following removal of the arsenic, the arsenic-depleted solution can be further processed to separate a recoverable metal through metal refining. The arsenic-laden fixing agent can be filtered to recover and recycle a filtrate to the solution for additional treatment, as well as using a partially saturated fixing agent to remove arsenic from fresh solution. An arsenic-containing solution can be formed from arsenic-containing solids such as contaminated soils, industrial byproducts and waste materials.
1 . A method for separating arsenic from an arsenic-containing solution, the method comprising the steps of:
contacting an arsenic-containing solution with a first portion of fixing agent under conditions in which at least a portion of the arsenic is fixed by the fixing agent to yield a partially-depleted solution and an arsenic-laden fixing agent, wherein the fixing agent comprises a rare earth-containing compound;
separating the arsenic-laden fixing agent from the partially-depleted solution; and
contacting the partially-depleted solution with a second portion of 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.
2 . The method of claim 1 , wherein the arsenic-depleted solution comprises a recoverable metal from Group IA, Group IIA, Group VIII and the transition metals.
3 . The method of claim 2 , further comprising the step of combining the arsenic-depleted solution with a process stream in a metal refining process to separate the recoverable metal.
4 . The method of claim 2 , further comprising precipitating the recoverable metal from the arsenic-depleted solution.
5 . The method of claim 2 , further comprising electrolyzing the arsenic-depleted solution to separate the recoverable metal.
6 . The method of claim 1 , wherein the step of contacting the partially-depleted solution with the second portion of fixing agent yields a partially-saturated fixing agent, the method further comprising the step of:
separating the partially-saturated fixing agent from the arsenic-depleted solution.
7 . The method of claim 6 , further comprising:
contacting the partially-saturated fixing agent with a fresh portion of an arsenic-containing solution under conditions in which at least a portion of the arsenic is fixed by the partially-saturated fixing agent to give a second partially-depleted solution and an arsenic-laden fixing agent; and
separating the second partially-depleted solution from the arsenic-laden fixing agent.
8 . The method of claim 7 , further comprising contacting the second partially-depleted solution with a third portion of fixing agent under conditions in which at least a portion of the arsenic is fixed by the fixing agent to give an arsenic-depleted solution.
9 . The method of claim 2 , 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.
10 . The method of claim 1 , wherein the rare earth-containing compound comprises one or more of cerium, lanthanum, or praseodymium.
11 . The method of claim 10 , wherein the rare earth-containing compound comprises a cerium-containing compound derived from cerium carbonate.
12 . The method of claim 10 , wherein the rare earth-containing compound comprises cerium dioxide.
13 . 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 first portion of fixing agent.
14 . The method of claim 13 , wherein the arsenic-containing solution has a pH of less than about 4 when the arsenic-containing solution is contacted with the first portion of fixing agent.
15 . The method of claim 14 , wherein the arsenic-containing solution has a pH of less than about 3 when the arsenic-containing solution is contacted with the first portion of fixing agent.
16 . 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 first portion of fixing agent.
17 . The method of claim 16 , wherein the arsenic-containing solution has a pH of more than about 9 when the arsenic-containing solution is contacted with the first portion of fixing agent.
18 . The method of claim 17 , wherein the arsenic-containing solution has a pH of more than about 10 when the arsenic-containing solution is contacted with the first portion of fixing agent.
19 . The method of claim 1 , wherein the arsenic-containing solution comprises more than about 1000 ppm sulfate when the arsenic-containing solution is contacted with the first portion of fixing agent.
20 . The method of claim 1 , further comprising the step of forming the arsenic-containing solution by contacting an arsenic-bearing material with a leaching agent comprising one or more of an inorganic salt, an inorganic acid, an organic acid and an alkaline agent.
21 . The method of claim 20 , wherein the alkaline agent comprises sodium hydroxide.
22 . The method of claim 1 , wherein the arsenic-depleted solution comprises arsenic in an amount of less than about 20 ppm.
23 . The method of claim 1 , wherein the first portion of fixing agent is substantially free of arsenic prior to contacting the arsenic-containing solution.
24 . The method of claim 1 , wherein the first portion of fixing agent is at least partially-saturated with arsenic.
25 . The method of claim 24 , wherein the fixing agent partially-saturated with arsenic comprises between about 0.1 mg and about 80 mg of arsenic per gram of fixing agent.
26 . An apparatus for separating arsenic from an arsenic-containing solution, the apparatus comprising:
a first contact zone adapted to receive an arsenic-containing solution, the first contact zone having fixing agent for contacting the arsenic-containing solution and fixing at least a portion of the arsenic to yield a partially-depleted solution, wherein the fixing agent comprises a rare earth-containing compound;
a second contact zone adapted to receive the partially-depleted solution, the second contact zone having fixing agent for contacting the partially-depleted solution and fixing at least a portion of the arsenic to yield an arsenic-depleted solution; and
a first separator disposed intermediate the first contact zone and the second contact zone for separating fixing agent from the partially-depleted solution.
27 . The apparatus of claim 26 , wherein the rare earth-containing compound comprises one or more of cerium, lanthanum, or praseodymium.
28 . The apparatus of claim 27 , wherein the rare earth-containing compound comprises a cerium-containing compound derived from cerium carbonate.
29 . The apparatus of claim 27 , wherein the rare earth-containing compound comprises cerium dioxide.
30 . The apparatus of claim 26 further comprising a second separator connected to the second contact zone for separating the arsenic-depleted solution from fixing agent.
31 . The apparatus of claim 30 , wherein the second separator comprises an outlet for providing fluid communication with the first contact zone for directing a partially saturated fixing agent to the first contact zone.
32 . The apparatus of claim 26 , further comprising a filtration unit operable connected to the first separator for receiving the arsenic-laden fixing agent and producing a filtrate.
33 . The apparatus of claim 32 , wherein the filtration unit comprises an outlet for providing fluid communication with the first contact zone for directing the filtrate to the first contact zone.
34 . The apparatus of claim 26 , further comprising a metal recovery unit connected to the second contact zone for separating a recoverable metal from the arsenic-depleted solution.
35 . The apparatus of claim 34 , wherein the metal recovery unit comprises one or more of a precipitation vessel and an electrolyzer.