US5120447A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method for removing heavy metals from wastewater
Assignee: Osram Sylvania Inc
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Filing: 1991-03-06
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Granted: 1992-06-09
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Expires: 2011-03-06
Abstract
Abstract A method for treating wastewater having a pH of between about 0.1 and 14 and containing dissolved heavy metals, in which a substantial portion of the heavy metals is precipitated as crystallized solids embedded within an insoluble monoclinic calcium sulfate crystal to produce a purified effluent having a pH of between 8 and 9.
Inventors
- 👤 Joel B. Christian
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 14:40
CPC Classifications
C; C02; C02F; C02F9/00; C02F1/00; C02F1/52; C02F1/5236; C02F2101/00; C02F2101/10; C02F2101/20; Y; Y10; Y10S; Y10S210/00; Y10S210/902; Y10S210/911; Y10S210/912
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
232 words
A method for treating wastewater having a pH of between about 0.1 and 14 and containing dissolved heavy metals, said method comprising the steps of: a) mixing an aqueous solution containing at least 100 gram per liter of a calcium compound selected from the group consisting of calcium chloride and calcium hydroxide with monoclinic calcium sulfate crystals to form a seeding solutio; b) combining said seeding solution and said wastewater to form a wastewater solution in which additional crystals of monoclinic calcium sulfate are formed on said monoclinic calcium sulfate crystals; c) adding a reagent to said wastewater solution to gradually adjust the pH of said wastewater solution to a desired range in order to promote the formation and growth of additional monoclinic calcium sulfate crystals and simultaneously precipitate a majority of said dissolved heavy metals as metal hydroxides, said majority of said metal hydroxides being embedded in said monoclinic calcium sulfate crystals to form crystallized solids, said embedded metal hydroxides thereby being prevented from redissolving into said wastewater solution; d) separating the liquid portion of said wastewater solution from said crystallized solids to obtain a purified effluent having a pH of between 8 and 9; e) filtering said purified effluent to produce a filtered purified effluent; f) discharging said filtered purified effluent to the environment; and g) reusing a portion of said crystallized solids in said seeding solution in step (a).
Claim 2
Independent Claim
232 words
A method for treating wastewater having a pH of between about 0.1 and 14 and containing dissolved heavy metals, said method comprising the steps of: a) mixing an aqueous solution containing at least 100 gram per liter of a calcium compound selected from the group consisting of calcium chloride and calcium hydroxide with monoclinic calcium sulfate crystals to form a seeding solutio; b) combining said seeding solution and said wastewater to form a wastewater solution in which additional crystals of monoclinic calcium sulfate are formed on said monoclinic calcium sulfate crystals; c) adding a reagent to said wastewater solution to gradually adjust the pH of said wastewater solution to a desired range in order to promote the formation and growth of additional monoclinic calcium sulfate crystals and simultaneously precipitate a majority of said dissolved heavy metals as metal hydroxides, said majority of said metal hydroxides being embedded in said monoclinic calcium sulfate crystals to form crystallized solids, said embedded metal hydroxides thereby being prevented from redissolving into said wastewater solution; d) separating the liquid portion of said wastewater solution from said crystallized solids to obtain a purified effluent having a pH of between 8 and 9; e) filtering said purified effluent to produce a filtered purified effluent; f) discharging said filtered purified effluent to the environment; and g) reusing a portion of said crystallized solids in said seeding solution in step (a).
Claim 3
Dependent Claim
31 words
The method of claim 1 wherein said heavy metals are selected from the group consisting of elements from groups TA through VTTA, TR through VTTB, and VTTT of the periodic table.
Claim 4
Dependent Claim
28 words
The method of claim 2 wherein said heavy metals are selected from the group consisting of copper, nickel, lead, zinc, arsenic, tantalum, selenium, molybdenum, cobalt, tungsten and cadmium.
Claim 5
Dependent Claim
32 words
The method of claim 1 wherein said wastewater contains at least one member selected from the group consisting of hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, sodium hydroxide and calcium hydroxide.
Claim 6
Dependent Claim
26 words
The method of claim 1 wherein said reagent is selected from the group consisting of hydrochloric acid, sulfuric acid, calcium hydroxide, magnesium hydroxide and sodium hydroxide.
Claim 7
Dependent Claim
11 words
The method of claim 5 wherein said reagent is calcium hydroxide.
Claim 8
Dependent Claim
11 words
The method of claim 5 wherein said reagent is sulfuric acid.
Claim 9
Dependent Claim
18 words
The method of claim 1 wherein said reagent is added to said wastewater in at least two steps.
Claim 10
Dependent Claim
16 words
The method of claim 1 wherein said reagent is added to said wastewater in three steps.
Claim 11
Dependent Claim
19 words
The method of claim 1 wherein the pH of said wastewater solution is adjusted to between 8 and 9.
Claim 12
Dependent Claim
41 words
The method of claim 1 wherein said liquid portion of said wastewater solution is separated from said crystallized solids by clarifying means in which suspended solids are agitated and act as nucleating agents to accelerate the precipitation of said crystallized solids.
Claim 13
Dependent Claim
13 words
The method of claim 11 wherein said clarifying means is a reactor clarifier.
Claim 14
Dependent Claim
14 words
The method of claim 1 wherein said purified effluent has a pH of 8.5.
Claim 15
Dependent Claim
28 words
The method of claim 1 wherein a flocculating agent is optionally added to said wastewater solution during said separating step to accelerate the precipitation of said crystallized solids.
Claim 16
Dependent Claim
13 words
The method of claim 14 wherein said flocculating agent is an anionic polymer.
Claim 17
Dependent Claim
36 words
The method of claim 1 wherein said seeding solution and said wastewater are agitated for a period of at least four hours to allow the formation and growth of said monoclinic calcium sulfate crystals to occur.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-06-09 | 1995-12-09 | 1996-06-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-06-09 | 1999-12-09 | 2000-06-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-06-09 | 2003-12-09 | 2004-06-09 | $7700.00 | Window Closed / Lapsed |