Patent Description:
Inorganic coagulants are chemicals that neutralize the surface charge of organic and inorganic colloidal particles contained in wastewater, thereby coagulating and settling the colloidal particles to facilitate the removal thereof. The inorganic coagulants have been used in the field of wastewater treatment for a long time. Among them, a coagulant containing aluminium sulfate, such as aluminium sulfate hydrate (called alum), is a typical inorganic coagulant used in wastewater treatment.

Wastewater from various industries, such as wastewater from the aluminium anodizing industry, wastewater from construction sites, and wastewater from the treatment process of used batteries, contains aluminium. To discharge industrial wastewater to nature, it is necessary to remove aluminium and other pollutants from the industrial wastewater. In this regard, the inorganic coagulants described above are mainly used to remove aluminium and pollutants from wastewater.

<CIT> discloses a process for removing metal contaminants, including aluminium, from contaminated industrial waste water by precipitating the metal compound contaminants from the waste water.

The present invention proposes a method of removing aluminium waste from wastewater.

A method of removing aluminium waste from wastewater according to the invention includes: (a) supplying wastewater containing aluminium as a feed, (b) separating the wastewater into a liquid component and a sludge component containing the aluminium, (c) reacting the sludge component and sulfuric acid to produce aluminium sulfate, (d) mixing the aluminium sulfate with alcohol to produce aluminium sulfate hydrate, and (e) adding the aluminium sulfate hydrate produced in step (d) to the wastewater supplied in step (a), to act as coagulant for the aluminium.

According to one embodiment, in the supplying of wastewater, the wastewater may have an aluminium content of <NUM> wt% or more, preferably <NUM> wt% or more, more preferably <NUM> wt% or more, calculated based on the weight of the aluminium ion without counter ions relative to the total weight of the waste water.

According to one embodiment, the aluminium comprised in the wastewater supplied in step (a) is at least in part comprised in an oxide or hydroxide form, preferably as boehmite (AlOOH).

According to one embodiment, the method additionally comprises adding externally sourced aluminium sulfate hydrate to the wastewater supplied in step (a).

According to one embodiment, the separating according to step (b) comprises centrifugation.

According to one embodiment, the sludge component obtained in step (b) has an aluminium content of <NUM> wt% or more, preferably <NUM> wt% or more, more preferably <NUM> wt% or more.

According to one embodiment, the reacting of the sludge component with sulfuric acid according to step (c) comprises adding the sludge component to of a sulfuric acid solution having a concentration of <NUM> to <NUM>, preferably <NUM> to <NUM>, at a temperature of <NUM> to <NUM> C, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, for <NUM> to <NUM> hours, preferably <NUM> to <NUM> hours, more preferably <NUM> to <NUM> hours.

According to one embodiment, the amount of the sludge component added to the sulfuric acid solution may be <NUM> to <NUM> wt% wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> to <NUM> wt%, based on the total weight of the (wet) sludge component and with respect to the weight of the sulfuric acid solution.

According to one embodiment, the alcohol mixed with the aluminium sulfate in step (d) comprises ethanol, propanol, butanol, or a combination thereof.

According to one embodiment, in the mixing of the aluminium sulfate with alcohol according to step (d), the aluminium sulfate and the alcohol are mixed in a volume ratio of <NUM>:<NUM> to <NUM>:<NUM><NUM>, preferably <NUM>:<NUM> to <NUM>:<NUM>, more preferably <NUM>:<NUM> to <NUM>:<NUM> (aluminum sulfate / alcohol). The volume of aluminium sulfate is understood as the volume of the combined sulfuric acid solution including the sludge.

According to one embodiment, in the adding of the aluminium sulfate hydrate to the wastewater, the amount of the aluminium sulfate hydrate added to the wastewater may be <NUM> to <NUM> ppm based on the mass of the wastewater, calculated based on the weight of the aluminium sulfate (mono or higher)hydrate without counter ions relative to the total weight of the waste water.

According to one embodiment, the method may further include supplying the aluminium sulfate hydrate to a separate wastewater treatment plant.

By a method according to the invention, aluminium waste can be removed environment-friendly and cost-effectively.

The above and other objectives, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.

<FIG> is a flowchart of a method of removing aluminium waste from wastewater, according to one embodiment;.

The method according to the invention of removing aluminium waste from wastewater includes: (a) supplying wastewater containing aluminium as a feed, (b) separating the wastewater into a liquid component and a sludge component containing the aluminium, (c) reacting the sludge component with sulfuric acid to produce aluminium sulfate, (d) mixing the aluminium sulfate with alcohol to produce aluminium sulfate hydrate, and (e) adding the aluminium sulfate hydrate produced in step (d) to the wastewater of step (a).

The wastewater in the supplying step may be any wastewater that contains aluminium. Additionally, the aluminium in the wastewater may be present in any form. For example, the aluminium contained in the wastewater may be in an oxide form and/or a hydroxide form.

In one embodiment, the aluminium-containing wastewater supplied as a feed may have an aluminium content of <NUM> wt% or more. Specifically, the wastewater may have an aluminium content of at least <NUM> wt%, preferably at least <NUM> wt%, and more preferably at least <NUM> wt%. Since the wastewater may have a high aluminium content, boehmite in the wastewater may be highly pure.

In one embodiment, the aluminium waste may contain boehmite (AlOOH). As described below, the aluminium waste contained in the wastewater can be regenerated into aluminium sulfate hydrate, which can be used as a coagulant by the method of the present invention. In particular, aluminium sulfate hydrate is typically obtained by the Bayer method in which sulfuric acid is reacted with alumite (Al(OH)<NUM>), which is obtained by reacting an aluminium-containing compound such as bauxite with NaOH and crystallizing the reaction product. Therefore, the composition of the aluminium waste is not particularly limited if the aluminium waste contains aluminium. On the other hand, boehmite can be converted to aluminium sulfate hydrate by direct reaction with sulfuric acid without going through the Bayer method described above. Therefore, in terms of process simplification and cost reduction, the aluminium waste can preferably include boehmite.

The method of the invention includes step (b) of separating the wastewater into a liquid component and a sludge component containing aluminium. The step is a process of separating the wastewater into a liquid component and an aluminium-containing sludge component which is used to produce aluminium sulfate hydrate. For example, the separation may be performed by centrifugation. Preferably, the separation may be performed by the addition of a coagulation, stirring, and precipitation of the sludge component. The liquid component may contain insoluble suspended solids and a tract amount of residual aluminium that has not been separated as the sludge component. The liquid component may be processed in a separate wastewater treatment plant and then be discharged to nature.

In one embodiment, the sludge component may contain <NUM> wt% or more of aluminium. The sludge component may contain more than <NUM> wt% of aluminium. When the aluminium content is converted to a boehmite content, more than <NUM>% of boehmite may be contained. Such a high boehmite content can increase the yield of aluminium sulfate obtained from the sludge component in later stages. The aluminium content of the sludge component may be preferably <NUM> wt% or more and more preferably <NUM> wt%.

According to one embodiment, the step of separating the wastewater into a liquid component and a sludge component may involve adding externally sourced aluminium sulfate hydrate. As described above, the step of separating the wastewater into a liquid component and a sludge component is preferably performed by adding a coagulant to settle and separate the sludge component. Here, aluminium sulfate hydrate may be used as a coagulant. The aluminium sulfate hydrate used in this step may be externally sourced aluminium sulfate hydrate rather than aluminium sulfate hydrate regenerated from aluminium waste present in the wastewater. The externally sourced aluminium sulfate hydrate may be added to the wastewater at any point in time. For example, in step (e) of the method, the externally sourced aluminium sulfate hydrate may be added to the wastewater at an early stage, for example, before aluminium sulfate hydrate regenerated from aluminium waste present in the wastewater is introduced into the wastewater. Alternatively, the externally sourced aluminium sulfate hydrate may be added to the wastewater as an additional coagulant after the aluminium sulfate hydrate regenerated from aluminium waste present in the wastewater is introduced into the wastewater to further promote coagulation and separation of the sludge component.

The method further includes step (c) of mixing sulfuric acid with the sludge component to produce aluminium sulfate. Aluminium, especially boehmite, contained in the sludge component reacts with the sulfuric acid and changes to aluminium sulfate according to the following reaction formula:.

(Reaction Formula <NUM>)     2AlOOH + <NUM><NUM>SO<NUM> → Al<NUM>(SO<NUM>)<NUM> + <NUM><NUM>O.

In one embodiment, step (c) may involve stirring. This may aid to increase the reaction rate by facilitating contact between the sludge component and sulfuric acid. The aluminium sulfate produced by the reaction exists as a supernatant in a mixture of the sludge component and the sulfuric acid, and the aluminium sulfate is recovered by separating only the supernatant from the mixture.

In one embodiment, the step of reacting the sludge component with sulfuric acid may be carried out with the use of a sulfuric acid solution having a concentration of <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> at a temperature of <NUM> to <NUM> for <NUM> to <NUM> hours. The sulfuric acid solution with a concentration of <NUM> is preferred in terms of convenience in constructing process equipment.

When the temperature is lower than <NUM> in the step of reacting the sludge component with sulfuric acid, the heat required Reaction Formula <NUM>, which is an endothermic reaction, is not sufficiently supplied, and thus the yield of aluminium sulfate decreases. When the temperature is higher than <NUM>, since the reverse reaction occurs, the yield of aluminium sulfate decreases. In one embodiment, the step of reacting the sludge component with sulfuric acid may be preferably performed at a temperature of <NUM> to <NUM> and more preferably at a temperature of <NUM> to <NUM>.

The step of reacting the sludge component with sulfuric acid may be performed for <NUM> to <NUM> hours. When the reaction time is shorter than <NUM> hour, since the time for mixing the sludge component with sulfuric acid is not sufficient, the reaction may not easily occur. In addition, when the reaction time is longer than <NUM> hours, the process cost increases significantly, and the yield of aluminium sulfate is not good for the process cost. In this step, the reaction time may be preferably <NUM> to <NUM> hours and more preferably <NUM> to <NUM> hours.

In one embodiment, the amount of the sludge component relative to the weight of the sulfuric acid solution may be in a range of <NUM> to <NUM> wt%. When the amount of the sludge component is less than <NUM> wt% relative to the weight of the sulfuric acid solution, a large amount of unreacted sulfuric acid solution remains, which reduces reaction efficiency. When the amount is more than <NUM> wt%, there is difficulty in stirring. In the step of reacting the sludge component with sulfuric acid, the amount of the sludge component may be preferably <NUM> to <NUM> wt% and more preferably <NUM> to <NUM> wt%, based on the weight of the sulfuric acid solution.

The method further includes step (d) of mixing the aluminium sulfate with alcohol to produce aluminium hydroxide hydrate. The aluminium sulfate produced by Reaction Formula <NUM> is insoluble in alcohol. Therefore, when aluminium sulfate and alcohol are mixed, precipitation occurs to produce aluminium sulfate hydrate, which is a solid phase. More specifically, when aluminium sulfate and alcohol are mixed, aluminium sulfate precipitates in the form of an anhydride (Al<NUM>(SO<NUM>)<NUM>), and water as binding water binds to the anhydrous aluminium sulfate during the precipitation, thereby producing aluminium sulfate hydrate (Al<NUM>(SO<NUM>)<NUM>·xH<NUM>O). Aluminium sulfate can be used as a coagulant, but aluminium sulfate hydrate, which is a more concentrated form produced by precipitation, is superior to aluminium sulfate in terms of coagulation ability.

According to one embodiment, in the step of mixing aluminium sulfate with alcohol, the alcohol may be ethanol, propanol, butanol, or a combination thereof. Since the hydrated aluminium sulfate is insoluble in alcohol, alcohol can be used to convert aluminium sulfate to aluminium sulfate hydrate. In terms of cost, as the alcohol, ethanol is preferred.

According to one embodiment, in the step of mixing aluminium sulfate with alcohol, the volume ratio of the aluminium sulfate to the alcohol may be in a range of from <NUM>:<NUM> to <NUM>:<NUM>. The volume ratio described above is advantageous in terms of the efficiency of the generation and precipitation of aluminium sulfate hydrate. Specifically, the volume ratio of the aluminium sulfate to the alcohol may be in a range of <NUM>:<NUM> to <NUM>:<NUM>, preferably a range of <NUM>:<NUM> to <NUM>:<NUM>, and more preferably a range of <NUM>:<NUM> to <NUM>:<NUM>.

The method further includes step (e) of adding the aluminium sulfate hydrate produced in step (d) to the wastewater of step (a). As described above, when the aluminium sulfate hydrate is supplied to the wastewater, the aluminium sulfate hydrate serves as a coagulant that neutralizes the surface charge of organic and inorganic colloidal particles contained the wastewater so that the colloidal particles can be easily coagulated and settled. In this way, the aluminium sulfate hydrate can remove colloidal particles contained in wastewater.

The aluminium sulfate hydrate added to the wastewater in step (e) is obtained by using aluminium contained in the wastewater as a raw material. Therefore, the method of the present invention can remove waste, particularly aluminium-containing waste, from wastewater while minimizing the usage of externally sourced coagulants, thereby enabling cost-effective wastewater treatment.

In one embodiment, in the step of adding the aluminium sulfate hydrate to the wastewater, the amount of the aluminium sulfate hydrate added to the wastewater may <NUM> to <NUM> ppm relative to the mass of the wastewater. In one embodiment, the regenerated aluminium sulfate hydrate is introduced into the wastewater in the presence of externally sourced aluminium sulfate hydrate. In this case, it is possible to reduce the usage of externally sourced aluminium sulfate hydrate that is used to coagulate and remove the sludge component containing aluminium.

In one embodiment, the method may further include the step of supplying the aluminium sulfate hydrate to a separate wastewater treatment plant. The liquid component separated from the wastewater may contain insoluble suspended solids as well as a trace amount of residual aluminium that has not been separated as the sludge component. The liquid component may be fed to a separate wastewater treatment plant, and aluminium sulfate hydrate as a coagulant may also be fed to the plant to coagulate and remove the residual aluminium and insoluble suspended solids.

In other words, the method of the present invention minimizes the amount of an externally sourced coagulant, and generates aluminium sulfate hydrate that can be used as a coagulant from aluminium waste contained in wastewater, thereby enabling value-added waste recycling. The method of the present invention is a two-stage wastewater treatment process in which wastewater is first separated into a liquid component and a sludge component, and the liquid component is subsequently further processed in a separate wastewater treatment plant. Therefore, the method of the present invention can increase the efficiency of waste removal from the wastewater. Furthermore, since the coagulant supplied to the wastewater treatment plant is the aluminium sulfate hydrate generated from aluminium waste contained in wastewater, the method of the present invention can considerably reduce the cost of wastewater treatment.

Hereinafter, the preferred examples will be described to aid understanding of the present invention.

An exemplary method for removing aluminium waste contained in wastewater according to one embodiment of the present invention was performed at a laboratory scale in the sequence shown in <FIG>. Raw wastewater containing <NUM>% by mass of aluminium in the form of boehmite (AlOOH) was separated into a liquid component and a sludge component containing the boehmite by centrifugation. The separated sludge component was reacted with <NUM> of sulfuric acid solution at a temperature of <NUM>. The amount of the sludge component, which is a reactant, added to the <NUM> of sulfuric acid solution was <NUM> wt%, and the reaction time was <NUM> to <NUM> hours. Referring to <FIG>, it is possible to visually observe the difference in the amount of aluminium sulfate hydrate produced when the time for reaction between the sludge component and the sulfuric acid solution was varied to <NUM> hour, <NUM> hours, and <NUM> hours. The FTIR analysis results of the sludge component containing aluminium sulfate hydrate obtained through reaction between the sludge component and the sulfuric acid are shown in <FIG>. The results show a peak similar to the peak of the FTIR analysis of potassium aluminium sulfate (see the lower graph in <FIG>). Afterwards, the sludge component containing aluminium sulfate was mixed with ethanol in a volume ratio of <NUM>:<NUM> and left for <NUM> hours. Through the series of steps, aluminium sulfate hydrate precipitated. The precipitate, i.e., aluminium sulfate hydrate was added to distilled water to give an aluminium sulfate hydrate solution with a concentration of <NUM>/L. The solution exhibited a pH of <NUM> and was added to wastewater. The feed concentration of the aluminium sulfate hydrate added to the wastewater was approximately <NUM> ppm by mass. The wastewater into which the aluminium sulfate hydrate solution was added was stirred at <NUM> rpm for <NUM> minutes and then stirred at <NUM> rpm for <NUM> minutes. The appearance of the raw wastewater and treated water was observed, and the results are shown in <FIG>. That is, the images of the water observed before and after the addition of the aluminium sulfate hydrate solution are shown in <FIG>.

Claim 1:
A method of removing aluminium waste from wastewater, the method comprising:
(a) supplying wastewater containing aluminium as a feed;
(b) separating the wastewater into a liquid component and a sludge component containing the aluminium;
(c) reacting the sludge component with sulfuric acid to produce aluminium sulfate;
(d) mixing the aluminium sulfate with alcohol to produce aluminium sulfate hydrate; and
(e) adding the aluminium sulfate hydrate produced in step (d) to the wastewater supplied in step (a), to act as a coagulant for the aluminium.