1. Field of the Invention
The present invention relates to processes for treating spent pickle liquors and/or ferrous chloride. More particularly, the present invention the relates to process for treating such spent pickle liquor without the use of chlorine. The present invention also relates to processes for treating spent pickle liquor in which the end product of the treatment process is useful for other purposes.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The process of pickling steel mill products to remove iron scale is well known. Typically, the articles from which the iron scale is to be removed are placed in an acid pickling bath. The acid bath is most commonly a sulphuric acid bath in which the strength of the acid generally varies from about 5 to 7%. As the pickling operations proceed, the acid strength of the bath gradually reduces, and acid is added to maintain its strength. However, when the iron content of the bath, due to dissolved scale, increases to approximately 7% iron or 20% ferrous sulfate, the operation becomes inefficient and the operator starts to “kill” the bath which involves allowing the bath to fall below 5% acid by not adding any more acid. The bath is then dumped and a new batch of acid is made up for pickling purposes.
The spent pickling bath is commonly referred to as waste pickle liquor and presents a disposal problem in that its acid and iron content renders it unsuitable for drainage into streams. Various methods have been proposed for neutralizing the waste pickle liquor. One method has been to add iron which reacts with the acid of the liquor to form iron sulfate which is then recovered by suitable processes. Another method of treating involves neutralizing the acid with an alkali such as lime, soda ash, or caustic soda.
The neutralization of waste pickle liquor with lime, soda ash, or caustic soda necessitates expensive equipment and many handling operations. It is necessary to provide proportioning apparatus for mixing the alkali with water to form a slurry. A mixer must be provided in which the slurry is mixed with the waste pickle liquor. In the case of caustic soda, a heat exchanger for cooling the material coming from the proportioning apparatus must be provided. From the mixing tank, the waste material must be transferred to a settling tank wherein the solids, mainly calcium sulfate, are allowed to settle from the liquid in which they are suspended. These solids form a sludge which presents another difficult and expensive disposal problem.
Another technique has been to add chlorine to the ferrous chloride component of the spent pickle liquor. The addition of this chlorine will create ferric chloride. The ferric chloride can then be utilized for other purposes.
Unfortunately, the use of chlorine is inherently difficult. Often, when chlorine is transported by train or by truck, accidents can occur which cause the release of hazardous chlorine into the environment. This can also evolve the evacuation of hundreds of persons from the surrounding area. Extensive clean-up efforts are required in order to remove the chlorine from the contaminated environment.
In other circumstances, special chlorine facilities are constructed in an area adjacent to the supply of the spent pickle liquor. The chlorine facilities are difficult and expensive to develop. Additionally, these processes also further add chlorine to the ferrous chloride. As such, further chlorine is introduced into the environment through the use of such facilities. As such, it is desirable to create a suitable product from the spent pickle liquor which does not involve the use of chlorine.
In the past, various patents have issued relating to the treatment of pickle liquor. For example, U.S. Pat. No. 2,433,458, issued on Dec. 30, 1947 to Kahn et al., describes a process for treating pickle liquor. This process involves the step of mixing the pickle liquor with an amount of an aqueous suspension of magnesium hydroxide sufficient to bring the pH of the pickle liquor to approximately 6.0. Ferric hydroxide is precipitated therefrom. The liquid is then separated from the precipitate. An amount of calcium hydroxide is then added so as to increase the pH of the pickle liquor to approximately 8.5. The balance of the iron can then be precipitated therefrom.
U.S. Pat. No. 2,583,098, issued on Jan. 22, 1952 to Heise et al., shows another process for the treatment of waste pickle liquor. This process involves the step of removing a pickling inhibitor from the pickle liquor and then passing the liquor to an electrolytic cell having a cathode upon which iron can plate and a porous anode. The liquor is electrolyzed in the cell at a temperature of up to 40° C. Iron from the liquor is plated onto the cathode and passed through the anode so as to oxidize only a portion ferrous iron into the liquor at the anode from the ferrous to the ferric.
U.S. Pat. No. 2,746,920, issued on May 22, 1956 to J. M. Wunderley, shows a process for the neutralization of spent pickle liquor. This process includes the steps of continuously feeding proportioned quantities of the liquor and a granulated blast furnace slag into a zone to form a slurry thereof. The slurry is continuously withdrawn from the zone. The withdrawn slurry is subjected to continuous mixing so as to cause the acid in the solution to be substantially neutralized and such that the solution is absorbed into the slag for reaction therewith. The reaction products are deposited upon inner and outer surfaces of the slag. The slag is continuously withdrawn for air drying and fixation of the reaction products in the slag.
U.S. Pat. No. 2,623,849, issued on Dec. 30, 1952 to H. L., Peterson, describes a method of treating spent ferrous material pickle liquor in which the mineral acids are neutralized. The metallic oxides are precipitated by introducing a neutralizing treating agent into this spent liquor. The neutralizing treating agent has a saponified fat content and an alkali content in a quality sufficient to effect a curd formation.
U.S. Pat. No. 2,775,508, issued on Dec. 25, 1956 to A. M. Thompsen, discloses a method of treating pickle liquors for the recovery of iron therefrom. The method includes the steps of forming a reagent solution consisting essentially of a mixture of a substantially iron-free aqueous solution of ammonium sulfate and the reaction products of ammonia and carbon dioxide. The reagent solution is added to the pickle liquor to precipitate, principally as iron carbonates, the major part of the iron resistance in the pickle liquor. The iron precipitate is removed by filtration to provide a solution of ammonium sulfate.
U.S. Pat. No. 3,211,538, issued on Oct. 12, 1965 to Gross et al., provides a process for the concentration of sulfuric acid pickle liquor. The ferrous sulfate is substantially completely recovered as solid ferrous sulfate mono-hydrate. The pickle liquor is combined with strong sulfuric acid to form a combined liquid stream. A hot drying gas stream is generated. The drying gas stream is accelerated to a high velocity by passing the drying gas stream downward to a passage defined by downwardly converging side walls. The combined liquid stream is in transverse contact with the accelerated stream of hot drying gas. The combined liquid stream is dispersed into the hot gas stream in the form of fine liquid droplets whereby sudden evaporation of liquid water into the gas stream takes place. The resulting moisture-laden gas stream is separated from the remaining liquid phase. The liquid phase is collected as a slurry of solid crystals of ferrous sulfate mono-hydrate in strong sulfuric acid. The solid crystals are filtered from the slurry.
U.S. Pat. No. 3,442,608, issued on May 6, 1969 to Addinall et al., provides a process for the regeneration of waste pickle liquors. An aqueous chlorine solution is fed in pulsed discreet portions into a reaction chamber. The reaction chamber is externally heated such that the reactants of the process are maintained separate from any product of combustion. An oxidizing atmosphere is provided for vaporizing free water and hydrochloric acid for the evolution of steam and gaseous hydrochloric acid with the attendant deposition of hydrated metal chloride on the heated surface and for oxidizing and dehydration the metal chloride and hydrolyzing the oxidize metal chloride by reaction with steam by vaporization of the aqueous solution fed to the heated surface in proximity to the oxidize metal chloride.
U.S. Pat. No. 4,149,946, issued on Apr. 17, 1979 to Z. L. Burke, discloses the recovery of spent pickle liquor and iron metals. The spent pickle liquor ion is regenerated and iron metal is recovered therefrom by electrolysis in a cell having an anode in an anode chamber and a cathode in a cathode chamber separated by a cation-selective membrane. The spent pickle liquor is placed in the cathode chamber and aqueous ammonium sulfate solution is placed in the anode chamber. Electrical current is passed through the cell. Ammonium ions pass through the membrane into the cathode chamber to form an aqueous ammonium sulfate solution. The ammonium sulfate anolyte is converted to sulfuric acid solution useful for pickling.
U.S. Pat. No. 5,057,290, issued on Oct. 15, 1991 to Peterson et al., discloses a process and apparatus for the low temperature recovery of ferrous chloride from spent pickle liquors. The process includes maintaining the hydrochloric, acid and iron concentrations within the spent pickle liquor at levels that will prevent the liquor from freezing when cooled to about −10°F. and that will permit the formation of ferrous chloride crystals within the spent pickle liquor when the liquor is cooled below about +10° F. to 20° F. and to about −10° F. The ferrous chloride crystals formed at such low temperatures are then removed from the pickle liquor. This permits reuse of the free hydrochloric acid remaining within the thus regenerated pickle liquor.
U.S. Pat. No. 5,344,572, issued on Sep. 6, 1994 to S. C. Wadhawan, discloses another method for treating waste pickle liquor. This method includes the steps of adding a flocculating agent to the pickle liquor solution, allowing at least some of the silica in the pickle liquor to begin to flocculate, again adding a flocculating agent to the pickle liquor solution, allowing the floccules containing silica to increase in size, and physically separating floccules from the pickle liquor solution.
It is an object of the present invention to provide a process for treating spent pickle liquor which avoids the addition of chlorine in the processes.
It is still another object of the present invention to provide a process for treating waste pickle liquor which avoids the use of hydrochloric acid.
It is another object of the present invention to provide a process for treating spent pickle liquor which avoids any transport of chlorine.
It is still another object of the present invention provide a process for treating spent pickle liquor which can effectively convert the ferrous chloride into a marketable product.
It is still another object of the present invention provide a process for treating spent pickle liquor which maximizes the amount of ferric chloride produced per liquid volume.
It is still another object of the present invention to provide a process for treating spent pickle liquor which produces a coagulant that can be useful in water treatment.
It is still a further object of the present invention to provide a process for treating spent pickle liquor which allows the reactions with the spent pickle liquor to be carried without adding heat to the process.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.