Method for the removal of metals, including a co-precipitation of molybdenum, from wastewater

• US 7,390,416 B1
• Filed: 01/25/2005
• Issued: 06/24/2008
• Est. Priority Date: 01/26/2004
• Status: Active Grant

• Current Assignee: American Airlines Incorporated (American Airlines Group Incorporated)
• Original Assignee: American Airlines Incorporated (American Airlines Group Incorporated)
• Inventors: Ede, Kenneth F., Thorson, Kerry C.
• Primary Examiner(s): Hruskoci; Peter A.
• Application Number:
  US11/042,661
• Time in Patent Office: 1,246 Days
• Field of Search: 210/725
• US Class Current: 210/725
• CPC Class Codes: C02F 1/5245 using basic salts, e.g. of aluminium and iron
• CPC Class Codes: C02F 1/56 Macromolecular compounds
• CPC Class Codes: C02F 1/66 by neutralisation; pH adjustment for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58
• CPC Class Codes: C02F 1/683 by addition of complex-forming compounds
• CPC Class Codes: C02F 11/121 by mechanical de-watering
• CPC Class Codes: C02F 2101/20 Heavy metals or heavy metal compounds
• CPC Class Codes: C02F 2103/44 from vehicle washing facilities
• CPC Class Codes: Y10S 210/912 Heavy metal
• CPC Class Codes: Y10S 210/913 Chromium

Abstract

An improved method to remove metals, including molybdenum, from industrial wastewater, by chemical precipitation of the metals, followed by settling and dewatering of the precipitate.

Claims

1. A method for treating wastewater, comprising:

(a) adding a metal sulfate comprising aluminum sulfate or alum to a wastewater containing metals comprising molybdenum and having a pH of from about 6 to 12, whereby the pH of the wastewater is lowered to from about 3.5 to 6.0;

(b) adding a hydroxyl providing base to the wastewater whereby the pH of the wastewater is raised to from about 8 to 10;

(c) adding a metal sulfide complex comprising an iron sulfide complex with a component comprising sodium dimethyldithiocarbamate to the wastewater;

(d) adding an acid to the wastewater whereby the pH of the wastewater is lowered to from about 3.2 to 3.7;

(e) adding a flocculating agent to the wastewater whereby the metals are precipitated as a precipitate; and

(f) separating the precipitate from the wastewater.

2. The method of claim 1 wherein the wastewater containing metals further comprises at least one of a metal selected from the group consisting of cadmium, copper, nickel, chromium, lead and zinc.

3. The method of claim 1 wherein the aluminum sulfate or alum is added in the range from 0.15% to 1.0% by weight of the wastewater.

4. The method of claim 1 wherein the aluminum sulfate or alum is added in the range from 0.15% to 0.35% by weight of the wastewater.

5. The method of claim 1 wherein the hydroxyl providing base is selected from the group consisting of sodium hydroxide, potassium hydroxide, and magnesium hydroxide.

6. The method of claim 1 wherein the acid is selected from the group consisting of phosphoric acid, sulfuric acid, and nitric acid.

7. The method of claim 1 wherein the flocculating agent comprises a high molecular weight anionic polymer.

8. The method of claim 1 wherein the precipitate settles by gravity by the use of a clarifier.

9. The method of claim 1 wherein the precipitate is separated from the wastewater by means of dewatering.