METHOD OF CLEANING CONTAINERS FOR RECYCLING
A method of cleaning recycled glass containers comprising exposing a container to a caustic solution and rinsing the container with a rinse solution is taught herein. The rinse solution comprises a chelating agent and optionally an acid, or an acid that can function as a chelator. Glass containers cleaned by the method are also described.
1 . (canceled)
2 . A method of cleaning a glass container comprising:
exposing the glass container to an aqueous caustic solution comprising a metal hydroxide; and
rinsing the glass container with a rinse solution having a pH of from 4 to 11 and comprising an effective amount of a chelating agent having at least an amine functional group, a carboxylic acid functional group, or a phosphorous-oxygen functional group.
3 . The method of claim 2 wherein the rinse solution further includes an acid.
4 . The method of claim 2 wherein the metal hydroxide is an alkali metal hydroxide.
5 . The method of claim 3 wherein the alkali metal hydroxide is NaOH or KOH.
6 . The method of claim 2 wherein the aqueous caustic solution comprises from 1 to 5 wt % metal hydroxide.
7 . The method of claim 6 wherein the alkali metal hydroxide is NaOH or KOH.
8 . The method of claim 2 wherein the pH of the rinse solution has a pH in the range of from 5 to 9.
9 . The method of claim 2 wherein the rinse solution has a pH in the range from 6 to 8.
10 . The method of claim 2 wherein the amount of chelating agent is effective to reduce heavy metal residing on or subsequently leaching from the surface of the glass container.
11 . The method of claim 10 wherein the amount of chelating agent is sufficient to provide free chelating agent in the rinse solution.
12 . The method of claim 10 wherein the rinse solution comprises at least 1 ppm free chelating agent.
13 . The method of claim 10 wherein the rinse solution comprises at least 5 ppm free chelating agent.
14 . The method of claim 10 wherein the rinse solution comprises 0.5-100 ppm free chelating agent.
15 . The method of claim 10 wherein the rinse solution comprises 5-10 ppm free chelating agent.
16 . The method of claim 2 wherein the rinse solution comprises from 0.0001 to 1 wt % chelating agent.
17 . The method of claim 2 wherein the chelating agent is EDTA, EGTA, NTA, DTPA, HEIDA, IDS, MGDA, gluconic acid, 2,2′-bipyridyl, phosphonic acid, complex phosphates, a mixture thereof or salts thereof.
18 . The method of claim 3 wherein the acid is a mono-, di-, or polycarboxylic acid.
19 . The method of claim 3 wherein the acid is acetic, oxalic, malic, maleic, fumaric, tartaric, citric, aspartic, glutamic, succinic acid, a mixture of any two or more thereof, or salts thereof.
20 . The method of claim 3 wherein the acid is a chelator.
21 . The method of claim 3 wherein the acid concentration is from 0.001 to 1.0 wt. %.
22 . The method of claim 2 wherein the rinse solution further comprises a buffer.
23 - 25 . (canceled)
26 . The method of claim 2 , wherein the temperature of the aqueous caustic solution is in the range of 30° C. to 80° C.
27 . The method of claim 2 , wherein the glass container comprises an applied ceramic label.
28 . The method of claim 2 , wherein the exposed, rinsed glass container yields less than 20 ppb heavy metal in a solution comprising 500 ppm phosphoric acid stored in the glass container for at least 10 minutes.