Title of Invention	AN IMPROVED PROCESS FOR BENEFICIATION OF PICKLING WASTEWATER WITH SIMULTANEOUS RECOVERY OF HYDROCHLORIC ACID AND FERROUS SULFATE
Abstract	The present invention relates to the Process for the Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate . The process is continuous in nature and recovery of HCL is 30 % by wt. Process steps are; concentrating pickling wastewater containing hydrochloric acid and iron upto 50% of original volume in a known manner at a temperature in the range of 110-120°C,adding continuously concentrated sulphuric acid in equal molar ratio to the said concentrated pickling wastewater in evaporator reactor, removing mother liquor containing ferrous sulphate from the bottom of the reactor, recycling part of the mother liquor to the reactor to maintain equilibrium concentration of HCL vapors above azeotropic concentration, recovering HCL vapours by known condensation method and ferrous sulphate resulting in crystal form by conventional crystallization methods.

Title of Invention

AN IMPROVED PROCESS FOR BENEFICIATION OF PICKLING WASTEWATER WITH SIMULTANEOUS RECOVERY OF HYDROCHLORIC ACID AND FERROUS SULFATE

Abstract

The present invention relates to the Process for the Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate . The process is continuous in nature and recovery of HCL is 30 % by wt. Process steps are; concentrating pickling wastewater containing hydrochloric acid and iron upto 50% of original volume in a known manner at a temperature in the range of 110-120°C,adding continuously concentrated sulphuric acid in equal molar ratio to the said concentrated pickling wastewater in evaporator reactor, removing mother liquor containing ferrous sulphate from the bottom of the reactor, recycling part of the mother liquor to the reactor to maintain equilibrium concentration of HCL vapors above azeotropic concentration, recovering HCL vapours by known condensation method and ferrous sulphate resulting in crystal form by conventional crystallization methods.

Full Text	The present invention relates to the Process for the Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate The wastewater generated at the steel rolling mill is the mixture of acid rinse water and spent pickle liquor having high concentration of hydrochloric acid and Iron. Resource recovery based process has been developed in the present invention for the treatment of spent pickle liquor. The process recovers hydrochloric acid for reuse in the pickling process, and iron in the form of ferrous sulfate which have commercial value. The operation of "hot rolling" in steel making process causes a layer of iron oxide, commonly referred to as "mill scale", to form on the surface of the processed steel. Before rerolling of hot rolled steel this scale is removed by running the processed steel through hydrochloric acid pickling lines, which comprise a series of tanks containing acidic solutions at varying concentrations and temperatures. The pickling process loosens and dissolves the fine mill scale and produces a bright, clean surface. Two effluent streams, viz. acid rinse water and spent pickling liquor are generated in the process of pickling. These liquid effluents are neutralized with alkali and disposed, in normal practice. The disposal of pickling liquors without treatment is a potential cause of environmental pollution due to high acid and iron content. Hauling spent acid offsite is hazardous as also cost prohibitive, and carries significant legal liability. Average pollutant concentrations in the pickling wastewater using hydrochloric acid as pickling agent are presented in Table 1. Table 1 : Typical Characteristics of Wastewater Generated in Acid Pickling (Table Removed) All values except pH and Conductivity are expressed in mg/L. * us/cm. ND - Not detectable Lowering the pH of well waters adjacent to disposal sites, intrusion of chlorides and salinity in soils and drinking water sources, hydrolysis of ferrous salts to ferrous-ferric hydroxides insoluble in water, and formation of ochre colored sediment, adverse effect on flora & fauna due to proliferation of ferreginous bacteria together with the ferrite deposits, and build up of high concentrations of dissolved iron in water sources are some of the major hazards due to disposal of untreated pickling wastes. The hitherto known physico-chemical treatment process for acidic wastewater management comprises neutralization using lime, and aeration for precipitation of iron. Neutralization of acidic effluents from pickling section by lime produces calcium chloride and iron (II) hydroxide. Calcium chloride is highly soluble in water and therefore it remains in treated wastewater. The concentration of chlorides in the treated wastewater therefore exceeds the permissible limit for effluent discharge. Iron (II) hydroxide upon exposure to air gets partially converted to iron (III) oxide, which imparts reddish colour to the soil. The neutralized wastewater is conventionally subjected to natural evaporation in solar ponds. The practice of adopting solar ponds for disposal of treated wastewater is unsuitable in view of high chlorides concentration in effluent. Non-specific removal of accumulated sludge and salts from the evaporation ponds also requires large area for ponds. The chloride concentration is further increased due to evaporation of water in the solar ponds. Also the evaporation rate is poor during monsoon months. Therefore such treatment plants, although accomplish neutralization, are not adequate to solve the problem effectively. The main object of the present invention is to provide an improved process for Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate for steel rolling mills, which obviates the drawbacks as detailed above, Process selection and development of treatment scheme presented in this invention is based on characteristics of typical wastewater as reported in Table I. Any variation in characteristics of wastewater can be handled, in the design of process, using waste specific design criteria determined through a treat ability study. In the drawing accompanying this specification, figure I represents the flow sheet of the process of recovery of hydrochloric acid and ferrous sulfate from pickling wastewater. The process comprises concentration of pickle liquor by evaporation, addition of dehydrating agent, viz. concentrated sulfuric acid, distillation of liquor for recovery of acid, and recovery of ferrous sulfate by crystallization from the saturated liquor remaining after distillation of hydrochloric acid gas. The treated wastewater can be safely discharged in the receiving water after neutralization or can be recycled after appropriate treatment. Accordingly the present invention provides an improved process for Beneficiation of Pickling Wastewater with simultaneous recovery of Hydrochloric Acid and Ferrous Sulfate, which comprises; i) concentrating pickling wastewater containing hydrochloric acid and iron upto 50% of original volume in a known manner at a temperature in the range of llO-120°C, ii) adding continuously concentrated sulphuric acid in equal molar ratio to the said concentrated pickling wastewater obtained in step (i) in evaporator reactor, removing mother liquor containing ferrous sulphate from the bottom of the reactor, iii) recycling part of the mother liquor to the reactor to maintain equilibrium concentration of HCL vapors above azeotropic concentration, iv) recovering HCL vapours resulting from (i) and (ii) by known condensation method and ferrous sulphate resulting in step (ii) in crystal form by conventional crystallization methods. In a preferred embodiment of the invention, the concentration is carried out at temperature of 110° C to 120° C and condensation of acid at 118° C to 123° C. In another embodiment of invention, concentrated sulfuric acid and concentrate is mixed in equal molar ratio for generation of concentrated hydrochloric acid gas in the reactor. Still in another embodiment, iron in the form of ferrous sulfate is recovered from the acid free effluent using crystallization The treatment process developed in the present invention consists of three stages as shown in figure 1. The numerals on the drawing refer to the unit operations involved in the process. In the first stage, the wastewater is concentrated through evaporation. In the second stage, the concentrated wastewater from the pre-evaporation stage is reacted with concentrated sulfuric acid to break the hydrochloric acid - water azeotrope and hydrochloric acid gas is collected through evaporation and absorbed in dilute acid to achieve 30% (w/w) Hydrochloric acid. In the third stage, the acid free wastewater from the second stage is cooled to recover crystalline ferrous sulphate. Stage 1 - In this stage, the spent pickling acid collected in the equalisation tank (1) is pre-evaporated to about 50% of its original volume in an evaporator (2) , operating at a temperature range of 108° to 110° C. Ferric chloride concentration in the liquid is thus increased to about 30% w/w. The concentrated liquor from stage 1 then passes to the second evaporator (3) in stage2 Stage 2 - Concentrated sulfuric acid (4) is added to the concentrated solution obtained from stage I. Ferric chloride in the effluent reacts with sulfuric acid to generate free hydrochloric acid gas which is recovered from the liquid by distillation. Ferrous chloride in the effluent is converted to ferrous sulfate. Hydrochloric acid gas is condensed distilled out in the stage II (3) at a temperature of 118° C to 123° C which is absorbed in the dilute hydrochloric acid (5) to make up the concentration of resultant acid to 30%, by recirculation (7) in packed bed absorber. Stage 3 - Concentration of ferrous sulfate in the liquid remaining after distillation of hydrochloric acid gas in stage 2 is appreciably high enabling recovery of ferrous sulfate through crystallization (6) by cooling. The diluted acidic effluent remaining after crystallization is recycled in the recovery section or neutralized and discharged. 85% of chloride contents in the spent pickling effluent is recovered in the form of hydrochloric acid and 90% iron is recovered in the form of ferrous sulfate ,from the raw spent pickling effluent. Examples Example 1 : Results of the Treatability Studies for steel plant 1 Pre-concentration Fresh spent acid was supplied after collection from identified sources of generation from a steel plant. Approximately 800 ml of raw spent acid was concentrated to 500 ml. It was observed that further concentration of the spent acid resulted in salting out of iron compounds. Distillate was collected and analysed. It was observed to contain about 40 gm/L HC1. Iron concentration in the concentrate increased by about 40 g/L. Concentrated spent acid generated in Stage I was taken in to the second stage reactor. Cone. H2SO4 was further added to the concentrate and the mixture was boiled. Mixture of HC1 and water vapour was collected from the top under vacuum, cooled and absorbed in dilute acid collected in pre-evaporation stage. Ferrous sulphate slurry was withdrawn from an outlet provided at the bottom of the reactor, and was kept aside for crystallisation studies. It was observed that almost 400 ml of concentrated sulphuric acid was required for complete reaction. Concentration of recovered HC1 could be maintained at 21% through controlled recirculation. The ferrous sulphate slurry collected from the bottom of the reactor was allowed to settle and anhydrous crystals were separated. Mother liquor was recycled back to the reactor. Anhydrous ferrous sulphate was hydrated by dissolving it in water. The solution was concentrated and cooled and FeSO4 H2O crystals were obtained. It was observed that 350 gm crystals could be obtained from the reaction mixture. The results of treatabilities studies are detailed in Table below. Table Results of Treatability Studies for Steel Plant 1 1. Pre-evaporation Volume of sample (ml) 800 Concentration (%) 75 Distillate volume (ml) 200 Cone, of HC1 in distillate (g/L) 40.1 Iron concentration in concentrate (g/L) 201 Time of pre-evaporation (hr.) 1.5 Temperature (°C) 106-116 2. Reactor Volume of Concentrate (ml) 600 Volume of cone, sulphuric acid (ml) 400 Volume of slurry (ml) 450 Volume of vapours (ml) 670 Cone, of HC1 in recovered acid (g/L) 241 Temperature (Range) (°C) 120 -130 3. Crystallisation Weight of anhydrous FeSO4(gm) 365 Quantity of water required for dissolution (ml) 770 Wt. of crystals FeSO4.7 H2O obtained (gm) 350 Volume of mother liquor remaining after 500 crystallisation (ml) Example 2 : Results of the Treatability Studies for steel plant 2 Pre-concentration Fresh spent acid was supplied after collection from identified sources of generation from steel plant 2. Approximately 800 ml of raw spent acid was concentrated to 500 ml. Distillate was collected and analysed. It was observed to contain about 43.1 gm/L HC1. Iron concentration in the concentrate increased by about 20 g/L. Concentrated spent acid generated in Stage I was taken in to the second stage reactor. Cone. H2SO4 was further added to the concentrate and the mixture was boiled. Mixture of HC1 and water vapour was collected from the top under vacuum, cooled and absorbed in dilute acid collected in pre-evaporation stage. Ferrous sulphate slurry was withdrawn from an outlet provided at the bottom of the reactor, and was kept aside for crystallisation studies. It was observed that almost 400 ml of concentrated sulphuric acid was required for complete reaction. Concentration of recovered HC1 could be maintained at 21% through controlled recirculation. The ferrous sulphate slurry collected from the bottom of the reactor was allowed to settle and anhydrous crystals were separated. Mother liquor was recycled back to the reactor. Anhydrous ferrous sulphate was hydrated by dissolving it in water. The solution was concentrated and cooled and FeSO4. H2O crystals were obtained. It was observed that 370 gm crystals could be obtained from the reaction mixture. The results of treatabilities studies are detailed in Table below. Table Results of Treatability Studies for Steel Plant 2 1. Pre-evaporation Volume of sample (ml) 800 Concentration (%) 75 Distillate volume (ml) 200 Cone, of HC1 in distillate (g/L) 43.8 Iron concentration in concentrate (g/L) 221 Time of pre-evaporation (hr.) 1.5 Temperature (°C) 106-116 2. Reactor Volume of Concentrate (ml) 600 Volume of cone, sulphuric acid (ml) 400 Volume of slurry (ml) 450 Volume of vapours (ml) 800 Cone, of HC1 in recovered acid (g/L) 200 Temperature (Range) (°C) 120 -130 3. Crystallisation Weight of anhydrous FeSO4 (gm) 395 Quantity of water required for dissolution (ml) 830 Wt. of crystals FeSO4.7 H2O obtained (gm) 370 Volume of mother liquor remaining after 660 crystallisation (ml) The main advantages of the invention are : • The acid recovery is carried out at a temperature of 130°C compared to hitherto known processes, recovering acid at 840°C, leading to appreciable energy and material savings • Use of sulfuric acid in the process chemically converts ferrous chloride to ferrous sulfate releasing hydrochloric acid gas. This enhances the total recovery of hydrochloric acid • Iron from the effluent is recovered in the form of ferrous sulfate with commercial value. Recovery of iron, in available processes, is in the form of oxide which has limited market compared to ferrous sulfate • As process operates at comparatively lower temperature, substantial energy saving can be achieved. Hydrochloric acid recovery is higher due the use of sulfuric acid, and iron is recovered in the form of ferrous sulfate with high market potential. Since the pickling wastewater is purified in the process alongwith the recovery of chloride ions and ion the process is environment friendly. The process is also highly cost effective as compared to hitherto known processes of pickling wastewater treatment. We Claim: 1. An improved process for beneficiation of Pickling wastewater with simultaneous recovery of Hydrochloric Acid and Ferrous Sulfate, which comprises; i) concentrating pickling wastewater containing hydrochloric acid and iron upto 50% of original volume in a known manner at a temperature in the range of llO-120°C, ii) adding continuously concentrated sulphuric acid in equal molar ratio to the said concentrated pickling wastewater obtained in step (i) in evaporator reactor, removing mother liquor containing ferrous sulphate from the bottom of the reactor, iii) recycling part of the mother liquor to the reactor to maintain equilibrium concentration of HCL vapors above azeotropic concentration, iv) recovering HCL vapours resulting from (i) and (ii) by known condensation method and ferrous sulphate resulting in step (ii) in crystal form by conventional crystallization methods. 2. A process claimed in claim 1 wherein the hydrochloric acid gas is recovered using gas absorption techniques. 3. A process claimed in claims 1 to 2 wherein ferrous sulfate is recovered using crystallization by cooling the liquid left in evaporator reactor after acid gas removal. 4. An improved process for the beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate is herein described with reference to the drawing accompanying the specification.

Full Text

The present invention relates to the Process for the Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate
The wastewater generated at the steel rolling mill is the mixture of acid rinse water and spent pickle liquor having high concentration of hydrochloric acid and Iron. Resource recovery based process has been developed in the present invention for the treatment of spent pickle liquor. The process recovers hydrochloric acid for reuse in the pickling process, and iron in the form of ferrous sulfate which have commercial value.
The operation of "hot rolling" in steel making process causes a layer of iron oxide, commonly referred to as "mill scale", to form on the surface of the processed steel. Before rerolling of hot rolled steel this scale is removed by running the processed steel through hydrochloric acid pickling lines, which comprise a series of tanks containing acidic solutions at varying concentrations and temperatures. The pickling process loosens and dissolves the fine mill scale and produces a bright, clean surface. Two effluent streams, viz. acid rinse water and spent pickling liquor are generated in the process of pickling. These liquid effluents are neutralized with alkali and disposed, in normal practice.
The disposal of pickling liquors without treatment is a potential cause of environmental pollution due to high acid and iron content. Hauling spent acid offsite is hazardous as also cost prohibitive, and carries significant legal liability. Average pollutant concentrations in the pickling wastewater using hydrochloric acid as pickling agent are presented in Table 1.

Table 1 : Typical Characteristics of Wastewater Generated in Acid Pickling

(Table Removed)
All values except pH and Conductivity are expressed in mg/L.
* us/cm.
ND - Not detectable
Lowering the pH of well waters adjacent to disposal sites, intrusion of chlorides and salinity in soils and drinking water sources, hydrolysis of ferrous salts to ferrous-ferric hydroxides insoluble in water, and formation of ochre colored sediment, adverse effect on flora & fauna due to proliferation of ferreginous bacteria together with the ferrite deposits, and build up of high concentrations of dissolved iron in water sources are some of the major hazards due to disposal of untreated pickling wastes.
The hitherto known physico-chemical treatment process for acidic wastewater management comprises neutralization using lime, and aeration for precipitation of iron.
Neutralization of acidic effluents from pickling section by lime produces calcium chloride and iron (II) hydroxide. Calcium chloride is highly soluble in water and therefore it remains in treated wastewater. The concentration of chlorides in the treated wastewater therefore exceeds the permissible limit for effluent discharge.
Iron (II) hydroxide upon exposure to air gets partially converted to iron (III) oxide, which imparts reddish colour to the soil. The neutralized wastewater is conventionally subjected to natural evaporation in solar ponds. The practice of adopting solar ponds for disposal of treated wastewater is unsuitable in view of high chlorides concentration in

effluent. Non-specific removal of accumulated sludge and salts from the evaporation ponds also requires large area for ponds. The chloride concentration is further increased due to evaporation of water in the solar ponds. Also the evaporation rate is poor during monsoon months. Therefore such treatment plants, although accomplish neutralization, are not adequate to solve the problem effectively.
The main object of the present invention is to provide an improved process for Beneficiation of Pickling Wastewater with simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate for steel rolling mills, which obviates the drawbacks as detailed above, Process selection and development of treatment scheme presented in this invention is based on characteristics of typical wastewater as reported in Table I. Any variation in characteristics of wastewater can be handled, in the design of process, using waste specific design criteria determined through a treat ability study. In the drawing accompanying this specification, figure I represents the flow sheet of the process of recovery of hydrochloric acid and ferrous sulfate from pickling wastewater.
The process comprises concentration of pickle liquor by evaporation, addition of dehydrating agent, viz. concentrated sulfuric acid, distillation of liquor for recovery of acid, and recovery of ferrous sulfate by crystallization from the saturated liquor remaining after distillation of hydrochloric acid gas. The treated wastewater can be safely discharged in the receiving water after neutralization or can be recycled after appropriate treatment.
Accordingly the present invention provides an improved process for Beneficiation of Pickling Wastewater with simultaneous recovery of Hydrochloric Acid and Ferrous Sulfate, which comprises;
i) concentrating pickling wastewater containing hydrochloric acid and iron
upto 50% of original volume in a known manner at a temperature in the range
of llO-120°C, ii) adding continuously concentrated sulphuric acid in equal molar ratio to the
said concentrated pickling wastewater obtained in step (i) in evaporator
reactor, removing mother liquor containing ferrous sulphate from the bottom
of the reactor, iii) recycling part of the mother liquor to the reactor to maintain equilibrium
concentration of HCL vapors above azeotropic concentration, iv) recovering HCL vapours resulting from (i) and (ii) by known condensation
method and ferrous sulphate resulting in step (ii) in crystal form by
conventional crystallization methods.

In a preferred embodiment of the invention, the concentration is carried out at temperature of 110° C to 120° C and condensation of acid at 118° C to 123° C. In another embodiment of invention, concentrated sulfuric acid and concentrate is mixed in equal molar ratio for generation of concentrated hydrochloric acid gas in the reactor.
Still in another embodiment, iron in the form of ferrous sulfate is recovered from the acid free effluent using crystallization
The treatment process developed in the present invention consists of three stages as shown in figure 1. The numerals on the drawing refer to the unit operations involved in the process. In the first stage, the wastewater is concentrated through evaporation. In the second stage, the concentrated wastewater from the pre-evaporation stage is reacted with concentrated sulfuric acid to break the hydrochloric acid - water azeotrope and hydrochloric acid gas is collected through evaporation and absorbed in dilute acid to achieve 30% (w/w) Hydrochloric acid. In the third stage, the acid free wastewater from the second stage is cooled to recover crystalline ferrous sulphate.
Stage 1 - In this stage, the spent pickling acid collected in the equalisation tank (1) is pre-evaporated to about 50% of its original volume in an evaporator (2) , operating at a temperature range of 108° to 110° C. Ferric chloride concentration in the liquid is thus increased to about 30% w/w. The concentrated liquor from stage 1 then passes to the second evaporator (3) in stage2
Stage 2 - Concentrated sulfuric acid (4) is added to the concentrated solution obtained from stage I. Ferric chloride in the effluent reacts with sulfuric acid to generate free hydrochloric acid gas which is recovered from the liquid by distillation. Ferrous chloride in the effluent is converted to ferrous sulfate. Hydrochloric acid gas is condensed distilled out in the stage II (3) at a temperature of 118° C to 123° C which is absorbed in the dilute hydrochloric acid (5) to make up the concentration of resultant acid to 30%, by recirculation (7) in packed bed absorber.
Stage 3 - Concentration of ferrous sulfate in the liquid remaining after distillation of hydrochloric acid gas in stage 2 is appreciably high enabling recovery of ferrous sulfate through crystallization (6) by cooling. The diluted acidic effluent remaining after crystallization is recycled in the recovery section or neutralized and discharged. 85% of chloride contents in the spent pickling effluent is recovered in the form of hydrochloric

acid and 90% iron is recovered in the form of ferrous sulfate ,from the raw spent pickling effluent.
Examples
Example 1 : Results of the Treatability Studies for steel plant 1
Pre-concentration
Fresh spent acid was supplied after collection from identified sources of generation from a steel plant. Approximately 800 ml of raw spent acid was concentrated to 500 ml. It was observed that further concentration of the spent acid resulted in salting out of iron compounds. Distillate was collected and analysed. It was observed to contain about 40 gm/L HC1. Iron concentration in the concentrate increased by about 40 g/L.
Concentrated spent acid generated in Stage I was taken in to the second stage reactor. Cone. H2SO4 was further added to the concentrate and the mixture was boiled. Mixture of HC1 and water vapour was collected from the top under vacuum, cooled and absorbed in dilute acid collected in pre-evaporation stage. Ferrous sulphate slurry was withdrawn from an outlet provided at the bottom of the reactor, and was kept aside for crystallisation studies. It was observed that almost 400 ml of concentrated sulphuric acid was required for complete reaction. Concentration of recovered HC1 could be maintained at 21% through controlled recirculation.
The ferrous sulphate slurry collected from the bottom of the reactor was allowed to settle and anhydrous crystals were separated. Mother liquor was recycled back to the reactor. Anhydrous ferrous sulphate was hydrated by dissolving it in water. The solution was concentrated and cooled and FeSO4 H2O crystals were obtained. It was observed that 350 gm crystals could be obtained from the reaction mixture.

The results of treatabilities studies are detailed in Table below.
Table Results of Treatability Studies for Steel Plant 1
1. Pre-evaporation
Volume of sample (ml) 800
Concentration (%) 75
Distillate volume (ml) 200
Cone, of HC1 in distillate (g/L) 40.1
Iron concentration in concentrate (g/L) 201
Time of pre-evaporation (hr.) 1.5
Temperature (°C) 106-116
2. Reactor
Volume of Concentrate (ml) 600
Volume of cone, sulphuric acid (ml) 400
Volume of slurry (ml) 450
Volume of vapours (ml) 670
Cone, of HC1 in recovered acid (g/L) 241
Temperature (Range) (°C) 120 -130
3. Crystallisation
Weight of anhydrous FeSO4(gm) 365
Quantity of water required for dissolution (ml) 770
Wt. of crystals FeSO4.7 H2O obtained (gm) 350
Volume of mother liquor remaining after 500
crystallisation (ml)

Example 2 : Results of the Treatability Studies for steel plant 2
Pre-concentration
Fresh spent acid was supplied after collection from identified sources of generation from steel plant 2. Approximately 800 ml of raw spent acid was concentrated to 500 ml. Distillate was collected and analysed. It was observed to contain about 43.1 gm/L HC1. Iron concentration in the concentrate increased by about 20 g/L.
Concentrated spent acid generated in Stage I was taken in to the second stage reactor. Cone. H2SO4 was further added to the concentrate and the mixture was boiled. Mixture of HC1 and water vapour was collected from the top under vacuum, cooled and absorbed in dilute acid collected in pre-evaporation stage. Ferrous sulphate slurry was withdrawn from an outlet provided at the bottom of the reactor, and was kept aside for crystallisation studies. It was observed that almost 400 ml of concentrated sulphuric acid was required for complete reaction. Concentration of recovered HC1 could be maintained at 21% through controlled recirculation.
The ferrous sulphate slurry collected from the bottom of the reactor was allowed to settle and anhydrous crystals were separated. Mother liquor was recycled back to the reactor. Anhydrous ferrous sulphate was hydrated by dissolving it in water. The solution was concentrated and cooled and FeSO4. H2O crystals were obtained. It was observed that 370 gm crystals could be obtained from the reaction mixture.

The results of treatabilities studies are detailed in Table below.
Table Results of Treatability Studies for Steel Plant 2
1. Pre-evaporation
Volume of sample (ml) 800
Concentration (%) 75
Distillate volume (ml) 200
Cone, of HC1 in distillate (g/L) 43.8
Iron concentration in concentrate (g/L) 221
Time of pre-evaporation (hr.) 1.5
Temperature (°C) 106-116
2. Reactor
Volume of Concentrate (ml) 600
Volume of cone, sulphuric acid (ml) 400
Volume of slurry (ml) 450
Volume of vapours (ml) 800
Cone, of HC1 in recovered acid (g/L) 200
Temperature (Range) (°C) 120 -130
3. Crystallisation
Weight of anhydrous FeSO4 (gm) 395
Quantity of water required for dissolution (ml) 830
Wt. of crystals FeSO4.7 H2O obtained (gm) 370
Volume of mother liquor remaining after 660
crystallisation (ml)
The main advantages of the invention are :
• The acid recovery is carried out at a temperature of 130°C compared to hitherto
known processes, recovering acid at 840°C, leading to appreciable energy and
material savings
• Use of sulfuric acid in the process chemically converts ferrous chloride to ferrous
sulfate releasing hydrochloric acid gas. This enhances the total recovery of
hydrochloric acid
• Iron from the effluent is recovered in the form of ferrous sulfate with commercial
value. Recovery of iron, in available processes, is in the form of oxide which has
limited market compared to ferrous sulfate
• As process operates at comparatively lower temperature, substantial energy saving
can be achieved. Hydrochloric acid recovery is higher due the use of sulfuric acid,
and iron is recovered in the form of ferrous sulfate with high market potential. Since
the pickling wastewater is purified in the process alongwith the recovery of chloride
ions and ion the process is environment friendly. The process is also highly cost
effective as compared to hitherto known processes of pickling wastewater treatment.

We Claim:
1. An improved process for beneficiation of Pickling wastewater with simultaneous
recovery of Hydrochloric Acid and Ferrous Sulfate, which comprises;
i) concentrating pickling wastewater containing hydrochloric acid and iron
upto 50% of original volume in a known manner at a temperature in the range
of llO-120°C, ii) adding continuously concentrated sulphuric acid in equal molar ratio to the
said concentrated pickling wastewater obtained in step (i) in evaporator
reactor, removing mother liquor containing ferrous sulphate from the bottom
of the reactor, iii) recycling part of the mother liquor to the reactor to maintain equilibrium
concentration of HCL vapors above azeotropic concentration, iv) recovering HCL vapours resulting from (i) and (ii) by known condensation
method and ferrous sulphate resulting in step (ii) in crystal form by
conventional crystallization methods.
2. A process claimed in claim 1 wherein the hydrochloric acid gas is recovered
using gas absorption techniques.
3. A process claimed in claims 1 to 2 wherein ferrous sulfate is recovered using
crystallization by cooling the liquid left in evaporator reactor after acid gas
removal.
4. An improved process for the beneficiation of Pickling Wastewater with
simultaneous Recovery of Hydrochloric Acid and Ferrous Sulfate is herein
described with reference to the drawing accompanying the specification.

Documents:

392-del-2000-abstract.pdf

392-del-2000-claims.pdf

392-del-2000-correspondence-others.pdf

392-del-2000-correspondence-po.pdf

392-del-2000-description (complete).pdf

392-del-2000-drawings.pdf

392-del-2000-form-1.pdf

392-del-2000-form-19.pdf

392-del-2000-form-2.pdf

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Patent Number

216825

Indian Patent Application Number

392/DEL/2000

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

19-Mar-2008

Date of Filing

31-Mar-2000

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG NEW DELHI-110001, INDIAN.

Inventors:

#	Inventor's Name	Inventor's Address
1	ANAND SURESHCHANDRA BAL	NATIONAL ENVIRONMENTAL ENGINEERING RESEARCH INSTITUTE, NEHRU MARG, NAGPUR, 440020 NAGPUR, MAHARASHTRA, INDIA.
2	ATUL NARAYAN VAIDYA	NATIONAL ENVIRONMENTAL ENGINEERING RESEARCH INSTITUTE, NEHRU MARG, NAGPUR, 440020 NAGPUR, MAHARASHTRA, INDIA.
3	MANUKONDA SURESH KUMAR	NATIONAL ENVIRONMENTAL ENGINEERING RESEARCH INSTITUTE, NEHRU MARG, NAGPUR, 440020 NAGPUR, MAHARASHTRA, INDIA.
4	PURUSHOTTAM KHANNA	NATIONAL ENVIRONMENTAL ENGINEERING RESEARCH INSTITUTE, NEHRU MARG, NAGPUR, 440020 NAGPUR, MAHARASHTRA, INDIA.

PCT International Classification Number

C02F

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA