EP2710160A2

EP2710160A2 - Recovery reactor

Info

Publication number: EP2710160A2
Application number: EP12726861.3A
Authority: EP
Inventors: Jaidev Rajnikant Shroff; Vikram Rajnikant Shroff; Krishna Ramprakash SRIVASTAVA; Jyeshtharaj Bhalchandra JOSHI
Original assignee: UPL Ltd
Current assignee: UPL Ltd
Priority date: 2011-05-20
Filing date: 2012-05-18
Publication date: 2014-03-26
Also published as: CN103562420B; CO6811845A2; WO2012160494A3; WO2012160494A2; BR112013029756A2; MX2013013522A; MX358085B; CN103562420A

Abstract

The present invention describes a recovery reactor with at least a settling zone, a reaction zone, and an overflow zone and a process for recovery of manganese from industrial effluent through treatment in the said recovery reactor wherein, the said recovered manganese has a uniform particle size.

Description

RECOVERY REACTOR

Field of the invention

The present invention relates to a recovery reactor and process thereof. More particularly, the invention relates to a reactor for recovery of minerals, particularly manganese from effluents and process for recovery of the same. Background of the invention

Industrial processes generate effluents containing metals such as Nickel, Manganese, Barium, Cobalt, and various other minerals that can be reused in various industrial processes. These effluents contain essential metals that are disposed off due to inadequate recovery methods. With growing environmental regulation, it is only prudent that minerals should be recovered from industrial effluents.

The prior art describes various methods for recovery of metals such as Nickel, Cobalt, Manganese etc. Manganese is a common metal found in effluents generated through manufacture of fungicides and other industrial products. It is essential that manganese be recovered from the effluent in an early stage of the treatment so as to avoid choking and scaling of treatment equipment, as well as to avoid potential environmental hazards of releasing such heavy metals into common disposal streams. The recovered manganese can be reused in the industrial manufacturing, thereby decreasing costs of production. Other industrial byproducts obtained on treatment may also be sold commercially leading to further profits as well as maintaining a green environment. US patent application US2009180945 (Mattioli et. al., 2009) describes a method of recovery of metals such as Ni, Co, Mn etc., through precipitation on reacting with ammonia wherein manganese is recovered as a hydroxide precipitate. The hydroxide precipitate is slimy and gelatinous and hence difficult to filter. Also, the hydroxides are readily converted to oxides under atmospheric conditions. It is difficult to convert oxides of manganese to another form through further reactions. The process disclosed involves several steps and a plurality of reactors, which take up much space and which is not cost-effective and economically feasible. The most commonly used method for recovery of manganese is to treat the effluent in a fluid-bed type of crystallizer. The resultant crystals obtained are not of a uniform particle size and require further treatment through milling to reduce particle size and to make it uniform. The resulting precipitate further causes choking. It is known that a process that results into crystallized manganese having a reduced particle size does not lead to severe choking of the apparatus, thereby increasing the desirability of producing manganese having a reduced and uniform particle size.

In common bubble type recovery reactors, a high rate of choking and scaling is observed in the bubble caps. Also, most reactor systems have more than one stage and more than one reactor vessels placed in tandem taking up valuable space and have high operating costs. The reactors known in the art have a separate compartment for collection of precipitate generated so as to avoid formation of impurities. The separate compartment takes up much space and it can be cumbersome to extract the precipitate from the compartment without additional equipment. The present invention provides a recovery reactor that allows for optimum recovery of manganese from effluents, wherein the manganese is obtained in its carbonate form having uniform particle size, thereby eliminating the expensive step of milling that is conventionally required to obtain uniform particle size. The apparatus of the present invention is a single unit, and does not incorporate any separate equipment for recovery and removal of the end product.

In an embodiment, the recovery reactor of the present invention is particularly suitable for being employed for the recovery of manganese from the mother liquor during the production process of EBDC fungicides, particularly mancozeb. The technical specification for mancozeb stipulates a minimum percentage content by mass of 20% in mancozeb. The process known for the manufacture of mancozeb comprises the following three major steps:

In the first step, NABAM i.e. the sodium salt of ethylene bis-dithiocarbamic acid is prepared by reacting ethylene diamine (EDA) with carbon disulfide and sodium hydroxide.

+

2H₂0

In the second step, the sodium salt of ethylene bis-dithiocarbamic acid is reacted with Manganese sulfate with agitation. Maneb is obtained as yellow crystals in slurry form. The said step of reacting the sodium salt of ethylene bis-carbamic acid with manganese sulfate to obtain maneb is carried out at a predetermined manganese concentration.

NABAM MANEB

In this step, during the addition of MnS0₄, the excess MnS0₄ content in the reactor is checked at regular intervals and maintained between 0.5-0.9%. After the complete addition of MnS0₄, the excess MnS0₄ content should be maintained between 0.6-0.9%.

In the third step, washed maneb is reacted with zinc sulfate to form mancozeb.

The mancozeb product so obtained is dried, in which the moisture content is brought to 10- 12% (spray dryer) and then to less than 1 % (rotary vacuum dryer).

There exists a need in the art for an apparatus and a method for recovering manganese from the effluent mixture in an intermediate step during the production of mancozeb.

Object of the invention

It is an object of the present invention to provide a single unit recovery reactor and settler that recovers manganese from an effluent mixture.

It is another object of the present invention to provide a recovery reactor that produces a precipitate of manganese carbonate having uniform particle size.

It is another object of the present invention to provide a recovery reactor that is cost effective and economically viable for recovery of heavy metals from effluent.

It is yet another object of the present invention to provide a process for the recovery of manganese using the recovery reactor.

It is a further object of the present invention to provide an apparatus and a method for recovering manganese from the effluent mixture in an intermediate step during the production of mancozeb. Summary of the invention

According to an aspect of the present invention there is provided a recovery reactor comprising: a) a settling zone, which is at a distal end of the recovery reactor, said settling zone comprising at least one outlet to recover settled precipitate;

b) a reaction zone, which has at least one impeller connected to a motor through at least one connecting rod, said reaction zone additionally comprising a plurality of inlet nozzles and a plurality of vertical baffles;

c) a calming zone comprising a plurality of horizontal baffles placed at the proximate, central, and distal ends of the zone; and

d) an overflow zone, said overflow zone including at least one outlet nozzle.

According to another aspect of the present invention there is provided a process for the recovery of manganese using a recovery reactor, said process comprising: a) providing a vertical recovery reactor, said recovery reactor comprising at least a settling zone, at least a reaction zone, at least a calming zone and at least an overflow zone;

b) introducing an effluent mixture comprising at least manganese as an impurity and co- introducing an alkaline reactant along with said effluent mixture into the reaction zone of the provided reactor;

c) causing the introduced effluent mixture and alkaline reactant to accelerate upward through the reaction zone, the upward acceleration in said effluent mixture and alkaline reactant being triggered due to rotation of an impeller provided at the bottom portion of the reaction zone;

d) adjusting the impeller rotation to a predetermined frequency such that uniformly sized manganese salt particles are precipitated;

e) collecting the precipitated particles from the settling zone through the provided outlet at the distal end of said settling zone;

f) allowing the manganese free effluent mixture to move in an upward direction through the provided calming zone into the overflow zone; and g) exiting the resultant effluent mixture through an outlet nozzle provided in said overflow zone.

According to yet another aspect of the present invention there is provided an improved process for the preparation of EBDC fungicides, said process comprising:

(a) reacting ethylene diamine with carbon disulfide and sodium hydroxide to obtain the sodium salt of ethylene bis-thiocarbamic acid;

(b) reacting the sodium salt of ethylene bis-carbamic acid with manganese sulfate to obtain maneb and separating maneb from the mixture;

(c) subjecting the mother liquor obtained in step (b) to a recovery process in a manganese recovery reactor, said recovery process comprising (a) providing a vertical recovery reactor, said recovery reactor comprising at least a settling zone, at least a reaction zone, at least a calming zone and at least an overflow zone; (b) introducing an effluent mixture comprising at least manganese as an impurity and co- introducing an alkaline reactant along with said effluent mixture into the reaction zone of the provided reactor; (c) causing the introduced effluent mixture and alkaline reactant to accelerate upward through the reaction zone, the upward acceleration in said effluent mixture and alkaline reactant being triggered due to rotation of an impeller provided at the bottom portion of the reaction zone; (d) adjusting the impeller rotation to a predetermined frequency such that uniformly sized manganese salt particles are precipitated; (e) collecting the precipitated particles from the settling zone through the provided outlet at the distal end of said settling zone; (f) allowing the manganese free effluent mixture to move in an upward direction through the provided calming zone into the overflow zone; (g) exiting the resultant effluent mixture through an outlet nozzle provided in said overflow zone; and (h) converting the recovered manganese carbonate into manganese sulfate and recycling the manganese sulfate in the reaction step of sodium salt of ethylene bis-carbamic acid with manganese sulfate to obtain maneb; and

(d) reacting maneb obtained in step (b) with zinc sulfate to obtain an EBDC fungicide, (e) drying the EBDC fungicide obtained in step (d). Brief Description of the drawings

The presented drawings are by way of illustration only and in no way limit the scope of the invention.

Fig. 1 is a cross section of an embodiment of a recovery reactor. Fig. 2 is a graphical representation of particle size density of precipitated particles at various velocities of the impeller.

Fig 3 is a graphical representation on the study of particle size distribution of precipitate obtained from a bubble cap type batch process reactor after milling versus the particle size distribution of precipitate obtained from the settling zone of the present invention. Detailed Description of the invention

Accordingly, in an aspect, the present invention provides a vertical recovery reactor comprising at least a settling zone, at least a reaction zone, at least a calming zone and at least an overflow zone. The said recovery reactor is a continuous type mixer settler reactor. The recovery reactor has vertical tubular structure with a varying circumference such that the circumference of the proximal end which houses the said overflow zone is wider as compared to the central calming zone and the reaction zone.

In an embodiment, the settling zone may be conically shaped and placed at the distal end of the reactor so as to enable collection of precipitate. The settling zone comprises at least one outlet for the removal of precipitate.

The reaction zone is a tubular structure with a uniform circumference attached to the settling zone at its distal end. The reaction zone comprises a plurality of inlet nozzles for introduction of industrial effluent and reacting chemicals. The reaction zone may also incorporate an impeller that is attached to a motor by means of a rod, wherein the said impeller is a down flow type with variable speed control that can be operated either manually or automatically. In an embodiment, the reaction zone comprises a plurality of vertical baffles placed diametrically opposite to each other and are placed at a position between said inlet nozzles and the said impeller such that at least one baffle is placed on diametrically opposite ends of the reactor walls. In this embodiment, the impeller and the vertical baffles help in even micro level mixing of the reactants. In this embodiment, the impeller speed is adjustable such that the micro-mixing of the effluent mixture and the alkaline reactant is completed. The impeller action causes the liquid to rise up, whilst allowing the heavier particles of favorable particle size to settle into the settling zone. In an embodiment, the impeller is disposed at an end of the reaction zone such that the settling of the particles in the settling zone is promoted. Surprisingly, the impeller is disposed at a location within the reaction zone and adjusted to rotate at a predetermined velocity such that the settlement of the fine particulates is not affected due to a rotational motion of the impeller.

The vertical baffles contribute towards ensuring the maximum mixing of the reactants within the reaction zone and prevent back mixing in the reaction zone. The placement of the vertical baffles ensures that the reaction is limited to the reaction zone and does not extend into the zones above or below the reaction zone. It has been found that at a predetermined rotational frequency of the impeller, particles having a uniform and desired particle size are produced.

The calming zone is a tubular structure with a uniform circumference attached to the reaction zone at its distal end and the overflow zone at the proximal end. The function of the calming zone is to essentially reduce the speed of the rising liquid and collect random particles of precipitate that may have travelled out of the reaction zone. In an embodiment, the calming zone comprises a plurality of horizontal baffles placed in the central, proximal, and distal parts of the calming zone. In this embodiment, at least two of the provided horizontal baffles are downward type of baffles with a center flow aperture adapted to slow down the speed of the reactant mixture. In yet another embodiment, the provided central horizontal baffle is a conical type baffle with annular flow. In this embodiment, the placement of the horizontal baffles creates a curved flow path that allows for particles of a large size to settle down, while at the same time, allowing the upward flowing mixture to travel smoothly into the overflow zone. The horizontal baffles also play a major role in collection of smaller particles that may have travelled upwards with the flowing manganese free mixture and in sending these smaller particles back to the reaction zone.

The overflow zone is tubular structure, wider than the circumference of the calming zone and the settling zone, and is placed at the proximal end of the reactor. In an embodiment, the overflow zone is attached to the calming zone at its least diameter end. The diameter of the overflow zone gradually increases upwards towards the provided outlet nozzle. The overflow zone is provided with at least one outlet nozzle which allows the removal of the manganese free effluent mixture, which has almost negligible particulates.

In an embodiment, the recovery reactor is a continuous type of mixer settler reactor. In another embodiment, the precipitate settled in the settling zone may be withdrawn from the settling zone on a continuous basis or at regular intervals, so as to maintain a particular level in the reactor.

In an embodiment of the present invention, the impeller may be a down ward type impeller with variable speed control and a range of velocities that can be operated either manually or automatically. The velocity or rotational frequency of the impeller may range from 80 to 200 rpm, which has been found to provide uniform particles having particle size in the range of 40 to 160μηη. It has been found that lower or higher rotation frequency of the impeller did not allow adequate separation of the manganese salt from the reaction mixture. Without wishing to be bound by theory, it is believed that at higher frequencies, the increased velocity of the flowing reaction mixture carries away even the heavier particles through the outlet nozzle while lower frequencies did not allow the particles to coalesce to form particles of sufficient size for settling down.

In an embodiment, the provided vertical and the horizontal baffles may be of any non reactive material, the vertical baffles may be preferably made up of a material such as glass. In another aspect, the present invention provides a process for the recovery of manganese using a continuous recovery reactor and settler. The process comprises providing a vertical recovery reactor, wherein, the reactor may have at least a settling zone, at least a reaction zone, at least a calming zone and at least an overflow zone. An alkaline reactant and an effluent mixture which may contain manganese as one of its impurities are simultaneously introduced into the reaction zone of the recovery reactor. The introduced effluent mixture and alkaline reactant are accelerated upward through the reaction zone, wherein, the reaction may cause the formation of a precipitate. The upward acceleration of the effluent mixture and alkaline reactant is caused due to the rotation of the impeller provided at the bottom portion of the reaction zone such that a change in the rotation frequency of the impeller causes consequential change in the velocity of the reaction mixture through the recovery reactor.

The precipitated particles settle in the settling zone and are recovered from the settling zone through the provided outlet at the distal end of the settling zone.

The manganese free effluent mixture moves in an upward direction through the provided calming zone into the overflow zone, where it is extracted through at least one outlet nozzle. The lighter precipitate particles which may have travelled upwards with the effluent mixture are caused to settle to the lower zones due to the horizontal baffles.

In an embodiment, the alkaline reactant is Na₂C0₃, preferably in the concentration of up to 20%. In this embodiment, the precipitate collected in the settling zone substantially comprises MnC0₃. The settled particles were found to possess a uniform particle size.

It was found that the concentration of the manganese impurity found in the un-reacted effluent mixture varied from 0 to about 0.5 ppm, and the precipitate obtained from the settling zone contained up to about 90% of recovered Manganese. It was further found that at an impeller frequency of about 80 rpm, the uniform particle size of the precipitate was about 60μηη. It was further found that when the impeller frequency was increased to about 120 rpm, the particle size of the precipitate was around 120μηη. At 150 and 175 rpm the particle size obtained was 90μ and 160μηη respectively while at about 200 rpm, the particle size obtained was 40μηη.

In an embodiment the impeller speed ranges between 80 to 200 rpm. More preferably ranges between 120 rpm to about 180 rpm.

Description of the preferred embodiments

Turning now to figure 1 , illustrated is a continuous type recovery reactor and settler as described in Fig.1. In addition the present invention relates to a process for recovery of manganese from industrial effluents in the form of MnC0₃. The manganese recovered from effluents may be reused in industrial processes.

With reference to Fig. 1 the vertical recovery reactor has settling zone A at the distal end of the reactor, a reaction zone B, a calming zone C, and an overflow zone D. The recovery reactor has tubular structure with a uniform circumference at the central section which houses zones B, and C, and the proximal end of the reactor which houses zone D with a circumference that is larger than that of the central section, and at the distal end has an inverted conical structure which houses zone A.

Zone A has an inverted conical shape and tapers towards the bottom of the reactor to end at outlet G. The precipitated end product settles in zone A, from here it can be removed through recovery outlet G. The precipitated end product may be recovered from outlet G at regular intervals so as to maintain a particular level in the reactor.

Zone B is the reaction zone, which has impeller E, wherein in one embodiment of the invention, the impeller E may be a downflow type impeller. Impeller E is attached to motor F by means of rod K, which runs along the entire length of the cylindrical part of the reactor to meet impeller E which may be positioned at the distal end of Zone B. Zone B has inlet nozzles 1 and 2 placed diametrically opposite to each other on the walls of the reactor. Inlet nozzles 1 and 2 introduce the reactants into the reactor. The position of inlet nozzles 1 and 2 enable the reactants to be introduced just above impeller E, thus allowing for maximum turbulence and mixing. Reaction zone B has vertical baffles 9, 10, 11 , 12 placed below inlet nozzles 1 and 2 on opposite sides of the reactor. The vertical baffles may have an elongated structure with variable length for each individual baffle and preferably made of glass. The vertical baffles may be attached two each on opposite walls of the reactor. As impeller E is a down flow type impeller, the particles remain in a suspended form, particles with large particle size settle down into settling zone A, while lighter particles remain suspended. The particle size depends upon the intensity of turbulence which is created by the action of impeller E.

Vertical baffles 9, 10, 11 , 12 play an important role in improving mixing inside the reaction zone, and in prevention of back mixing. The micro mixing allows for further improved mixing of the reactants and thus ensures quicker precipitation of the final product. The liquid in this section is forced in an upward direction, while the precipitate floats to settling zone A. Together, impeller E and vertical baffles 9, 10, 11 and 12 also ensure that the particle size of the precipitate is uniform, thus reducing the need for milling before further treatment of the end product. Zone C is the calming zone and is placed above reaction zone B. Zone C captures escaped precipitated lighter particles that have not settled in the settling zone, for this purpose zone C has three horizontal baffles placed at regular intervals. Horizontal baffle 5 is a downward type baffle and is placed at the distal end of zone C, and has a center flow aperture that ensures smaller particles move downward towards the Zone A. Horizontal baffle 5 is attached to the body of the reactor by means of gasket J1. The central horizontal baffle 6 is a conical type horizontal baffle and creates an annular flow space. Horizontal baffle 6 is supported by a plurality of supports placed below the said baffle. Horizontal baffle 7 is placed at the proximal end of zone C, wherein, horizontal baffle 7 is a downward type horizontal baffle with a central flow aperture. Horizontal baffle 7 is attached to the body of the reactor by means of gasket J2. The horizontal baffles 5, 6, 7 may be made from any non reactive material such as glass. The liquid reaction mixture traveling in an upward direction is forced through a curved path formed due to the unique placement of the horizontal baffles; the curved path further enables the leftover smaller particles of precipitate to move downwards to Zone A. Also, once the liquid mixture moves to the calming zone, there is no reaction taking place, as the liquid is essentially from manganese. Zone D is the overflow zone, and makes up the proximal end of the reactor. Zone D has a wider diameter as compared to the central zones B and C. The wider zone helps further decrease the velocity of the reactants moving upwards. The smaller particles that have escaped the horizontal baffles will settle down to the bottom, thus ensuring near total recovery of the precipitate. Zone D has overflow nozzle 8 placed at the side of the reactor wall. Overflow nozzle 8 lets out reaction mixture almost without any precipitate. On reaching zone D, the velocity of the reaction mixture is greatly reduced, this allows for remaining particles to settle down and move towards zone A.

The recovery reactor in one of the embodiments may be used to precipitate MnC0₃. In this particular embodiment, the effluent may contain industrial effluent containing manganese in its sulphate form as MnS0₄. The effluent is introduced into the reactor along with reactant Na₂C0₃ through nozzles 1 and 2. As the reactor is a continuous type reactor, the reaction may take place on a continuous basis and the volume of effluent added may be regulated through nozzles 1 and 2. As the reactants are introduced into the reactor, impeller E begins to stir the reactant mixture at a desired velocity, causing MnCo₃ to precipitate and settle into settling zone A. Through the actions of impeller E, the MnCo₃ obtained has a uniform particle size. The turbulence can be regulated by regulating the speed of the impeller so as to obtain various particle sizes Vertical baffles 9, 10, 11 , 12 ensure that back mixing does not occur. The quantity of manganese recovered from the effluent was about 90 to 95 % and manganese loss may be decreased to about 1 to 0.05%.

Fig. 2 depicts the particle size density of MnC0₃, obtained at different intensity of turbulence. It was found that at a specific velocity (frequency) of the impeller E, the particle size obtained was different. In Fig. 2,D10 represents those velocities at which the resultant particles produced were of such size that 10% of the particles pass through a mesh of 3 μηη (or are less than 3 μηη), D50 represents those velocities at which the resultant particles produced were of such size that 50% of the particles pass through a mesh of 30 urn (or are less than 30 urn), D90 represents those velocities at which the resultant particles produced were of such size that 90% of the particles pass through a mesh of 300 urn (or are less than 300 urn). Similarly, D100 represents those velocities at which the resultant particles produced were of such size that where 100% of the particles pass through the sieve. In one embodiment the velocity of the impeller is ranged between 80 to 200 rpm, so as to acquire a particle size that ranges between 120 μηη to 200 μηη.

The walls of the recovery reactor could be made up of stainless steel or glass, or any other non-corrosive material. The reactor could be of various sizes depending upon the volume of the effluent generated. Also, the dimensions of vertical baffles 9, 10, 11 , 12 could vary from rectangular to square.

In an embodiment of the present invention, the reactor is used to treat the effluent with manganese impurity released from the manufacturing units of Ethylenebisdithiocarbamates (EBDCs) compounds. EBDCs compounds are selected from the group of mancozeb, maneb, metiram, milnebmancopper, amobam, asomate, azithiram, carbamorph, cufraneb, cuprobam, disulfiram ferbam metam, nabam, tecoram, thiram, urbacide, ziram dazomet, etem, polycarbamate, propineb, zineb and the recovered manganese is reused in said manufacturing units.

Thus, in another aspect, the present invention provides an improved process for the preparation of EBDC fungicides, said process comprising:

(c) subjecting the mother liquor obtained in step (b) to a recovery process in a manganese recovery reactor, said recovery process comprising (a) providing a vertical recovery reactor, said recovery reactor comprising at least a settling zone, at least a reaction zone, at least a calming zone and at least an overflow zone; (b) introducing an effluent mixture comprising at least manganese as an impurity and co-introducing an alkaline reactant along with said effluent mixture into the reaction zone of the provided reactor; (c) causing the introduced effluent mixture and alkaline reactant to accelerate upward through the reaction zone, the upward acceleration in said effluent mixture and alkaline reactant being triggered due to rotation of an impeller provided at the bottom portion of the reaction zone; (d) adjusting the impeller rotation to a predetermined frequency such that uniformly sized manganese salt particles are precipitated; (e) collecting the precipitated particles from the settling zone through the provided outlet at the distal end of said settling zone; (f) allowing the manganese free effluent mixture to move in an upward direction through the provided calming zone into the overflow zone; (g) exiting the resultant effluent mixture through an outlet nozzle provided in said overflow zone; and (h) converting the recovered manganese carbonate into manganese sulfate and recycling the manganese sulfate in the reaction step of sodium salt of ethylene bis-carbamic acid with manganese sulfate to obtain maneb; and

(d) reacting maneb obtained in step (b) with zinc sulfate to obtain an EBDC fungicide.

(e) drying the EBDC fungicide obtained in step (d).

In an embodiment, the recovery reactor of the present invention is particularly suitable for being employed for the recovery of manganese from the mother liquor during the production process of EBDC fungicides, particularly mancozeb.

+

2H₂0

In the second step, the sodium salt of ethylene bis-dithiocarbamic acid is reacted with Manganese sulfate with agitation. Maneb is obtained as yellow crystals in slurry form.

NABAM MANEB

In this step, during the addition step of MnS0₄, the excess MnS0₄ content in the reactor is checked at regular intervals and maintained between 0.5-0.9%. After the complete addition of MnS0₄, the excess MnS0₄ content should be maintained between 0.6-0.9%. The excess manganese in the mixture of this step of the reaction is recovered using the method as described hereinbefore. The recovered manganese is recycled for further reaction with NABAM.

In the third step, washed maneb is reacted with zinc sulfate to form mancozeb.

MANCOZEB

Example 1

A fluid bed type of bubble cap crystallizer in semi batch operation was used to treat effluent containing about 3000ppm MnS0₄, with 9% Na₂C0₃. Instead of sludge, crystal pellets of MnC0₃ were obtained. Pallets with an approximate size of <250 μηη were obtained. The particle size obtained was not uniform. The side draw from the reactor yielded about 50ppm of Manganese which was sent for disposal. The precipitate obtained in the process did not have a uniform particle size.

A similar reaction with 9% Na₂C0₃and effluent containing 3000ppm MnS0₄ was carried out in the recovery reactor. The particles obtained were in the form a finely dispersed sludge, with a uniform particle size. The overflow from the reactor was subjected to Inductively Coupled Plasma-Mass Spectrometry. The result obtained showed less than 5ppm of Manganese in the overflow. The yield of MnC0₃ obtained was between 20 to 97%. The particle size obtained was 95 μηη at impeller velocity 150rpm and did not require milling for particle size reduction.

Further reactions were carried using 9% Na₂Co₃ using the recovery reactor and varying volumes of effluent was introduced into the reactor and % of manganese in the overflow nozzle was recorded as follows:

The overflow from the reactor was subjected to Inductively Coupled Plasma-Mass Spectrometry to determine quantity of Manganese.

Fig 3 is a comparison of the particle size of particles obtained from the fluid bed crystallizer after milling and the particle size of the particles obtained from Zone A of the recovery reactor. In Fig.3 D (Ax10) denotes particle size that could pass through the sieve or the cumulative fraction of particles which are below a certain particle size. Thus, in Fig 3 the particle size of the particles obtained from recovery reactor are below 200μηη.

Example 2

Using the process described above, effluent at volume of 100 Liters/ Hour was introduced through nozzle 1 and 20% Na₂Co₃ was introduced through nozzle 2, and reacted together at impeller speed of 80 RPM. The particle size density in each zone was as recorded as follows:

Zone A had up to 90% particle size density. The invention has been described above by way of illustration, and the specific embodiment disclosed is not intended to limit the invention to the particular forms disclosed. For example, the embodiments described in the foregoing were directed to providing a clear idea about the preferred modes, including the best mode, of making and using the present invention. However, in alternate embodiments, those skilled in the art may implement the invention without deviating from the central idea of the invention. The invention therefore covers all modifications, equivalents, and alternatives falling within the spirit and scope of the following claims

Claims

CLAIMS . A continuous type mixer settler recovery reactor for recovery of metals from effluents, said reactor comprising: a) a settling zone, which is at a distal end of the recovery reactor, said settling zone comprising at least one outlet to recover settled precipitate;

b) a reaction zone, which has at least one impeller connected to a motor through at least one connecting rod;

d) an overflow zone, said overflow zone including at least one outlet nozzle.

2. The continuous type mixer settler recovery reactor as claimed in claim 1 , wherein said reaction zone additionally comprises a plurality of inlet nozzles and a plurality of vertical baffles.

3. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said recovery reactor has vertical tubular structure with a varying circumference such that the circumference of the proximal end which houses the said overflow zone is wider as compared to the central calming zone and the reaction zone.

4. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims wherein said recovery reactor has an inverted conical structure at the distal end which houses the settling zone.

5. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said settling zone has an inverted conical shape tapering at the distal end to open into a recovery outlet.

6. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims wherein said impeller is a down flow type impeller with variable speed control that can be operated either manually or automatically.

7. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, comprising at least one nozzle provided for introduction of the effluent and at least one nozzle provided for the introduction of the reactant into said reaction zone.

8. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said plurality of vertical baffles are placed at a position between said inlet nozzles and the said impeller such that at least one baffle is placed on diametrically opposite ends of the reactor walls.

9. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein the calming zone includes at least three baffles.

10. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said horizontal baffle at the proximal end of the said calming zone is a downward type of baffle with a center flow aperture.

1 1 . The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said horizontal baffle at the distal end of the said calming zone is a downward type of baffle with a center flow aperture.

12. The continuous type mixer settler recovery reactor as claimed in any one of the preceding claims, wherein said horizontal baffle placed in the center is a conical type baffle with annular flow.

13. A process for the recovery of manganese using the continuous type mixer settler recovery reactor , said process comprising: a) introducing an effluent mixture comprising at least manganese as one of the impurities and co-introducing an alkaline reactant along with said effluent mixture into the reaction zone of the provided reactor; b) causing the introduced effluent mixture and alkaline reactant to accelerate upward through the reaction zone being triggered due to rotation of an impeller provided at the bottom portion of the reaction zone;

c) adjusting the impeller rotation to a predetermined frequency such that uniformly sized manganese salt particles are precipitated;

d) collecting the precipitated particles from the settling zone through the provided outlet at the distal end of said settling zone;

e) allowing the manganese free effluent mixture to move in an upward direction through the provided calming zone into the overflow zone; and f) exiting the resultant effluent mixture through an outlet nozzle provided in said overflow zone.

14. The process as claimed in claim 13, wherein the said alkaline reactant used in step (a) is Na₂C0₃ with a concentration upto 20%._.

15. The process as claimed in claim 13, wherein the particle size of the precipitate obtain in step (c) is from about 50-90μηη.

16. The process as claimed in claim 13, wherein the impeller speed ranges between 80 to 200 rpm, more preferably between 120 rpm to about 180 rpm.

17. An improved process for the preparation of EBDC fungicides, said process comprising:

(c) subjecting the mother liquor obtained in step (b) to a recovery process as claimed in claim 13;

(d) converting the manganese carbonate recovered in step (c) into manganese sulfate and using the said recovered manganese sulfate in the reaction step (b) to obtain maneb; and

(e) reacting maneb obtained in step (b) and step (d) with zinc sulfate to obtain an EBDC fungicide.

(f) drying the EBDC fungicide obtained in step (e).

18. The process as claimed in claim 17, wherein the EBDC fungicide is mancozeb.