Title of Invention

A BENCH SCALE UNIT WITH DATA ACQUISITION AND CONTROL SYSTEM FOR CHEMICAL LEACHING OF MINERALS AND A METHOD FOR THE SAME

Abstract

A BENCH SCALE UNIT WITH DATA ACQUISITION AND CONTROL SYSTEM FOR CHEMICAL LEACHING OF MINERALS AND A METHOD FOR THE SAME. A bench scale unit with data acquisition and control system for chemical leaching of minerals comprising of: - a batch reactor (11) with heating arrangement having a plurality of heating coils (26-29); - a condenser (12) with provision for reflux; - data acquisition and control system (13); - a host computer(15); - sparkler horizontal filter(16); - a stirrer (17) fixed inside the reactor (11); - a DC motor (14) to run the stirrer, and - a plurality of Resistance Temperature Detectors (RTD1, 2, 3) being positioned at bottom and 10cm and 20cm from the bottom of the reactor the bottom RTD1 being connected to PID controller (21) which controls the temperature inside the reactor.

Full Text

Field of Invention:- This invention relates to the field of chemical leaching in general and to a bench scale unit with data acquisition and control system for chemical leaching of minerals and a process for the same in particular. Background and prior art:- The process of liquid/solid extraction, also known as leaching, involves the transfer of a solute from a solid, generally employed in particulate form, to a liquid solvent which is termed the "extract". In this process, the solid imbibes the solvent which dissolves the solute and thereby extract it from the solid. Leaching is a very old process and a great diversity of apparatus has been developed over the years to meet the varying requirements of the process in respect to its widely diverse applications. Leaching processes have been proposed which operate in a batch, semi-batch or continuous mode, and both single-stage and multi-stage contacting techniques are used. Leaching equipment is commercially available for a wide variety of processes, including fixed-bed processes in which solvent is percolated through a stationery bed of solids, moving-bed processes in which the solids are conveyed through the solvent with little or no agitation, and dispersed -solid processes in which the solids are dispersed in the solvent by mechanical agitation. Among the many critical problems involved in the successful operation of a leaching process are those associated with the fact that the solid material to be leached is often quite heterogeneous in character, and therefore exceedingly difficult to treat in an optimum manner. This invention discloses a bench scale unit with data acquisition and control system where various minerals and metals can be extracted at elevated temperature and atmospheric pressure using the process of leaching. This invention also provides apparatus for dewatering and leach reactors which may be suitable for carrying out the leaching process. An effort has been made to design and develop a bench scale unit where up to 2Kg of ore can be treated. This will help in optimization as well as scaling up the chemical leaching process to commercial scale. In the present case, an example has been given for brief methodology to be followed for carrying out chemical leaching of coal using alkali and acid leaching method. However, this set up can be used for chemical leaching study of various other minerals using any other inorganic chemical including acid and alkalis. This set up can be used for detail kinetics, thermodynamics and energy requirement studies for extraction of minerals using existing chemical leaching process and also for development of new processes for extraction of other minerals using this leaching technique. Methodology, scientific background and few important test results using this set up have been discussed in the subsequent sections. Beneficiation is a variety of processes whereby extracted ore from mining is reduced to particles that can be separated into mineral and waste, the former suitable for further processing or direct use. It may be conducted via a range of techniques including crushing, grinding, magnetic separation, flotation, gravity etc. Beneficiation enables operators to improve the quality of their end product and to enhance the overall processing performance of an ore. Accordingly, physical as well as chemical cleaning (beneficiation) processes have been explored. In physical cleaning, the mineral is crushed into suitable particle size, and the waste is removed in processes based on the differences in their physical properties. Based on the physical properties that effect the separation of the coal from the impurities, physical cleaning methods are generally divided into the following categories: gravity, flotation magnetic and electrical. In contrast to physical cleaning, chemical processes involve addition of chemical which reacts with the mineral matter or waste and allow it to be easily removed. This includes mainly the process of liquid/solid extraction, also known as leaching, involves the transfer of a solute from a solid, generally employed in particulate form, to a liquid solvent which is termed the "extract" . In this process, the solid imbibes the solvent which dissolves the solute and thereby extracts it from the solid. U.S. Patent No. 6613271 discloses about an apparatus and methods for recovering valuable metals particularly gold using an in line leach reactor. This invention states about the apparatus and method for continuously separating a dense valuable material such as gold from a feed including a grinding mill which directs a crushed feed through hydrocyclones for separation into a light and dense fraction. The dense fraction is concentrated further by in line pressure jigs in line and the concentrate is leached in a rotating leaching reactor. The resulting pregnant liquor is subjected to eletrowinning to recover gold and the spent liquor is recycled. U.S. Patent No. 4824939 discloses about a novel leaching process which is useful for leaching a particulate solid material that comprises extractable and nonextractable portions. The process includes the steps of introducing the particulate solid material and a liquid solvent to an extraction zone; agitating the liquid solvent to a degree sufficient to suspend the particulate solid material and effect segregation of particles thereof in relation to their propensity to settle; maintaining contact between the liquid solvent and the particulate solid material for a time sufficient to leach extractable material therefrom: and selectively withdrawing particles from the extraction zone. In a preferred embodiment, the leaching process is a multi-stage process employing a series of stages in which the selectively withdrawn particles from each stage are introduced to the next successive stage of the series. U.S. Patent No.5993635 relates to a method of enabling a sulphide mineral composition to be leached at atmospheric pressure instead of above atmospheric pressure which has been hitherto required in order to achieve acceptable rates of leaching. In the case of the chemical leaching processes for removing ash from coal, the inorganic substances constituting the ash content of coal are treated with chemical agents and separated from the coal for removal. Various chemicals are used for the chemical beneficiation process. Some of these chemicals will have a tendency to dissolve certain inorganic constituents preferentially to others and the actual chemical to be used may depend upon the inorganic content of the carbonaceous material which is fed to the process. Chemical leaching of coal is a technology to produce ultra clean coal where the ash content of clean coal is as low as ~ 1.0% basing on mineralogical composition of the feed coal. There are potential use of this ultra clean coal both as a fuel and nonfuel. Such processes are known as processes for removing ash from coal or coke (Japanese Patent Publication No.466/1942), a process for removing sulfur and ash from coals (Japanese Patent Publication No. 23711/1971) and a coal deashing process (Japanese Patent Disclosure No. 133487/1980). The patent literature is replete with chemical coal beneficiation processes. For example, U.S. Patent No. 4,424,062, 4,071,328, 4,083,940, 4,134,737 and U.S. Patent No. 4,408,999 etc. discloses about processes for chemically removing ash from coal by treating ash containing coal in various chemical reagents at different operating conditions. Most of these studies have been carried out in laboratory scale using flask, rotamantle and beakers etc. where small quantity of coal can be treated. U.S. Patent No. 4,936,045 discloses about a set up where alkali and acid leaching of coal can be carried out in a 500 ml stainless pressure vessel under pressure at high temperatures. In this process the alkali and coal slurry passes through an electric emersion heater and finally passes through the leaching reactor where the removal of mineral matter takes place. However the prior art does not disclose any bench scale unit for conducting trial runs and experimentation of chemical leaching of minerals. A need is therefore felt that chemical leaching of minerals should be studied in small scale to optimize chemical leaching, where various data should be recorded for analysis and optimization of the process. The present invention seeks to overcome these drawbacks of the prior art. Objects of the invention:- 1. An object of the invention is to provide a bench scale unit to study chemical leaching of minerals. 2. Another object of the invention is to optimize a chemical leaching process. 3. A further object of the invention is to provide a facility for acquiring , storing and displaying various data related to a chemical leaching process for minerals. 4. Yet another object of the invention is to make a chemical leaching process most energy efficient. 5. A still further object is to project the actual energy needs of a full scale chemical leaching process for extraction of minerals, including coal. Brief description of accompanying drawings: 1. Schematic Diagram of Bench Scale unit for carrying out Chemical Treatment of coal 2. Schematic Diagram of heating control arrangement and energy data acquisition 3. Schematic Diagram of Data Acquisition and Control System 4. Temperature Profile during an experimentation using the bench scale set up 5. Energy Profile during an experimentation using the bench scale set up The invention will now be described in detail with the help of the accompanying which depict an exemplary embodiment of the invention. However, there can be several other embodiments of the invention, all of which are deemed covered by this description. Set up description: The bench scale unit (1.0) best shown in Fig.l consists of a batch reactor (11) of nearly 23 litres capacity with heating arrangements, condenser (12) with provision for reflux, data acquisition and control system (13) and sparkler horizontal filter(16). The batch reactor is of diameter 25cm and height 45cm. The reactor is made up of SS-316 material with Teflon coating. The reactor is heated with four heating coils (26-29) of 1-kilowatt capacity each which are fitted outside the circumference of the reactor. A stirrer (17) which extends up to nearly 5cm from the bottom of the reactor is fixed at the middle. A D.C. motor (14) runs the stirrer and its speed can be measured using a sensor which is mounted in front of the stirrer. It gives the stirrer speed by magnetic induction principle. The maximum rpm can go up to ~1500 and it can be controlled using a variac. However, the stirrer is usually operated at around 600-900rpm. Prepared reagents are kept inside bottles at a height from the reactor from where those are fed to the reactor using a manifold, pipes and connectors. There is facility for filling the reactor with coal slurry using pipes. As shown in Fig-2 three Resistance Temperature Detectors (RTD 1-3) are mounted at bottom and, 10cm and 20cm from the bottom of the reactor. The RTD 1 at the bottom is connected to the PID controller(21) through which the temperature inside the reactor can be controlled through relay switches (22- 25) connected to the heaters. The four relay switches can also be controlled manually by switching the relay on or off. Remaining two RTDs (RTD2&3) are connected to the data acquisition module (31) through a signal conditioning element(33). There is an energy meter (32) to sense the amount of current passing through the "Live wire" which provides electricity supply to the four heating coils(26-29). The output from this device (current data) is sent to host computer (15) for the following calculation. Power(kwhr)=Power(kwhr)+Voltage (volt)*Current (ampere) Energy=Power x time The temperature data from data acquisition module as well as controller, energy data etc can be seen on the host computer through a graphical user interface developed particularly for this set up. The details of the microprocessor based interfacing for data acquisition is described later. The data acquisition modules, PID controller, signal conditioning elements, 24 V battery, variac and display unit of stirrer etc are placed inside a panel. The schematic diagrams of the data acquisition and control modules is shown in Figures2 and 3. The bench scale unit also consists of a sparkler horizontal filter (16) having polypropylene filter cloths. The final coal/mineral slurry after treatment inside the reactor is filtered using a series of polypropylene filter cloth of 5-micron size. The filter cake is deposited on the top of the filter cloth. The filter cake is dried inside a drying oven having humidity control facility. The filter operates on a one HP pump. The intermediate samples are however filtered using normal filter papers using a conical flask and a funnel. Microprocessor Based interfacing of the sensors with Computer: It is achieved by using common hardware, well known in the prior art. Interfacing of the sensors with computers has wide applicability in industry. It can be used to get on-line from the process or to operate an instrument (relay or SSR etc.). 1-7000 modules (31) are compact, intelligent sensor-to- computer interface unit designed specifically for reliable operation in harsh environments. Encased in rugged industrial grade plastic packages, their built-in microprocessors let them independently provide intelligent signal conditioning, analog I/O, digital I/O, data display and RS-485 communication. These modules can be controlled remotely by a set of commands. They provide an extremely simple and cost effective way to allow any PC equipped with a serial port to carry out monitoring and control applications. Each Module has on board microprocessors for control, and communication is carried out over a 2 wire RS 485 communication link (35) at data rates up to 115 bps, and distances up to 1200m. A serial command and response protocol makes control of modules extremely easy from any high level language (Turbo C or Visual Basic), under any operating system. Analog Input Modules are available to monitor Thermocouples, RTD's, voltages and current signals. Readings are automatically converted to engineering format, and transmitted to host computer (15) on request. Output Modules either give current or voltage outputs with microprocessor controlled slew rate. In addition to the analog modules, a selection of digital I/O modules provide high voltage input, open collector and relay outputs. The 7000 series RS 485 network is among the most powerful and flexible 2 wire RS 485 network in the world. It is a multiple baud rate, and multiple data format network system. That is to say, all remote modules mentioned above share the same RS 485 network. The 7520, the RS 232 to RS 485 converter equips a "self tuner" inside. Therefore, it can detect the baud rate, and data format automatically and control direction of the RS 485 network precisely. Therefore the user can connect all this equipment to the same RS 485 network. This method greatly reduces system cost and increase reliability. The Host PC(15) will send out a command string from its RS 232 port. The 7520 will convert these RS 232 signals to RS 485 signals, and isolate the host from the RS network. The 7000 series modules will be directly connected to the RS485 network. The 2 wire RS 485 network is a pair of differential network. So, logically, the 2 lines equal to 1 data line. The data line can be used both to transfer command and receive results. This needs a direction controller to handle the 2 wire RS 485 network. The 7520, the RS 485 to RS 232 converter is an intelligent controller. It will automatically detect and control he direction of data flow. When the host compute sends a RS 232 command string, the 7520 sets the direction of RS 485 network in the received mode, and the 7000 series can receive the host command string. After the command string is finished, the 7520 will set the RS 485 network in send mode to allow the 7000 modules to send the result to the host computer. Sensors The RTD temperature Sensor (RTD1-3): The RTD is a sensor that operates on the principle that the resistance of a metal like platinum increases with an increase in temperature at a specific rate. The Resistance Temperature Detector is often selected when accurate temperature measurements are required. RTD's could be made of Copper, Nickel or Platinum. Currently, Platinum is the industry standard for the material use in making RTD's. As long as the temperature relationship with resistance is predictable, smooth, and stable, the phenomenon can be used for accurate temperature measurement. To ensure high accuracy, the resistance effects due to impurities must be small and the resistance versus temperature curve must be known and repeatable. Platinum RTD's are suitable for use from -50C to 550C, when long-term temperature stability and repeatability is required. They offer virtually a linear response over this range. The details of the two data acquisition module used in the present case has been described below. Modules 1.7520 Module This module provides the necessary serial bus protocol conversion from PC standard RS 232 to a 2 wire RS 485 interface. This module connects to all other modules on the RS 485 network. Its specification are: Input: RS 232C protocol Output: RS 485 protocol (2 wire, D+, D-) Baud Rate: "Self Tuner" auto switching baud rate, 300 to 115200bps. Modules: 256 modules maximum without repeater 2.7017 Module The 7017 is a 8-Channel Voltage and 4-20mA Input Module. It takes in an analog input Eight different inputs can be given to this module at a time at Channel 0 to Channel 7. Its specifications are Input type:mV,V,mA Input Range:+/- 150mV, +/-1 V, +/- 200mA Sample Rate: 10 samples per second Bandwidth: 13.1 Hz Accuracy: 0.01% or better Method for chemical leaching of minerals in the bench scale unit: In the present case a brief method is described for carrying out chemical leaching of coal using alkali and acid leaching method with the bench scale unit in accordance with the invention. This set up can be used for chemical leaching study of various other minerals using any other inorganic chemical including acid and alkalis under atmospheric condition. Here, West Bokaro fine clean coal was taken as a feed sample to this process. This fine clean coal is generated in West Bokaro coal washery through froth flotation process. The feed sample can be taken directly as obtained after froth flotation treatment or can be crushed to -72 BS mesh size (-0.025mm) for improving the kinetics of the process. Ash content of this coal sample was 13.1%. This West Bokaro fine clean coal is referred as feed coal in the subsequent section of this write up and the clean coal produced from this process is referred as Product. Sample Preparation: 1-2 kg of coal was taken through coning quartering method from the received West Bokaro fine clean coal. This coal sample was dried in an oven at 105°C. Chemicals: The experiments were carried out with various chemicals initially. However, since the presence of acidic compounds like silica and alumina in Indian coals are significantly higher, some chemicals tend to behave better than other chemicals. Treating such coals using dilute aqueous NaOH solution under mild conditions at atmospheric pressure followed by acid leaching/washing results in substantial demineralization of the coal. The alkali and acid used can be recovered for re-use. This affords a convenient method for coal demineralization. Commercially available sodium hydroxide (NaOH) in combination with sulphuric acid (H2S04) and HCI were used in the present method. The treatment process The experiments for chemical leaching were carried out in the reactor assembly using two steps. In the first step, feed coals(l-2 kg) were treated with varying concentration (10-50%) of alkali (NaOH) (10 lit) at varying temperatures under reflux with stirring for particular length of time (1.5-7.0 hr) in the bench scale reactor described above. The treated coal is then washed repeatedly with water and/or HCI and then dried. The washed alkali treated coal (10-50gm) is then reacted with 10-20% H2S04/ HCL for 1.0-5.0 hr keeping the same condition as described above. Then , the treated coal is filtered, washed with water and dried before sending for their chemical, rheological and petrographical properties. The coal to slurry ratio is maintained at 1:10 or 1:5 keeping the total volume 10 litres. The moment the feed is fed to the reactor, the stirrer and the data acquisition system are switched on. The readings are checked in the host computer using the GUI to ensure the proper working of the sensors. Once checked, the data are captured using the save command which saves the data to a text file. At the start of the experiment all the four heaters (26-29) are switched on. Any of the four heaters can be switched on or off based on requirement. For example, once the set point is reached, the set temperature can be controlled using only one heater. During the test, intermediate samples can be collected any time from the sampling pipe present at the bottom of the reactor. Different amount of sample can be collected at various length of time during the test basing on subsequent analysis to be one with the samples. The samples collected can be washed with water and/or 10-20% HCI/H2SO4 solution. These samples are dried and analyzed for various properties. After the completion of the experiment, the remaining sample present inside the reactor is taken out from the bottom and filtered using the sparkler horizontal filter. The filter cake is dried inside a drying oven and analyzed for various properties. Multi-stage experiments as well as intermediate dosing experiments were also carried out using the experimental set up. The experiments for chemical leaching of coal to remove mineral matter were conducted at various levels of reagent concentration, coal weight, coal to solution ratio and type of washing (only water or water and 10-20% H2SO4/HCI combined together). The samples were analyzed for ash, volatile matter alkali content (Na20 & K20), ash constituents (Fe, CaO, Si02/ AI203, MgO, MnO, Ti02, Phosphorous, and Sulphur etc.), calorific value (kcal/kg) and Crucible Swelling Number (CSN) etc. Using this set up when chemical treatment of West Bokaro fine clean coal were carried out, the ash content reduced from 13.1% to nearly 5.0%. With this set up the temperature profile during the experimentation as well as the energy requirement during the experimentation can be evaluated as can be seen from Figures 4 and 5. With the development of the present bench scale set up, the chemical cleaning process can be carried out in bench scale using a bigger size reactor with jacketed steam heating or electric heating arrangement as described above. Detail thermodynamic and kinetic study as well as energy requirement for this process can be evaluated using the bench scale unit. This will help in optimization as well scaling up the chemical leaching process to commercial scale and low ash coal can be produced economically for coke making. However, this set up can also be used for detail kinetics, thermodynamics and energy requirement studies for extraction of minerals using existing chemical leaching processes and also for development of new processes for extraction of other minerals using this leaching technique. Any chemical leaching process for extraction of minerals can therefore be studied with the help of the bench scale unit to determine the most efficient operating parameters to optimize the process, before a full-scale chemical leaching process is taken up. We Claim:- 1. A bench scale unit with data acquisition and control system for chemical leaching of minerals comprising of : - a batch reactor (11) with heating arrangement having a plurality of heating coils (26-29); - a condenser (12) with provision for reflux; - data acquisition and control system (13); - a host computer(15); - sparkler horizontal filter(16); - a stirrer (17) fixed inside the reactor (11); - a DC motor (14) to run the stirrer; - a plurality of Resistance Temperature Detectors (RTD1, 2, 3) being positioned at bottom and 10cm and 20cm from the bottom of the reactor the bottom RTD1 being connected to PID controller (21) which controls the temperature inside the reactor; - RTD2 and RTD3 being connected to data acquisition module (31) through signal conditioning element (31); - an energy meter (32) to sense the current supplied to the heating coils (26-29) characterized in that the bench scale unit generates, acquires and records a plurality of data for optimization of a chemical leaching process for minerals. 2. A bench scale unit as claimed in claim 1, wherein the heating coils (26-29) are of 1 kilowatt capacity each, and are filted outside the circumference of the reactor(ll). 3. A bench scale unit as claimed in claim 1, wherein the stirrer (17) has a sensor mounted on its front to measure the speed of the De motor (14) which runs the stirrer. 4. A bench scale unit as claimed in claim 1, wherein the PID controller (21) automatically controls the temperature inside the reactor through relay switches (21-25) connected to the heaters (26-29), provision for manually controlling the relay switches (21-25) being also provided. 5. A bench scale unit as claimed in claim 1, wherein various data from the data acquisition module (31) as well as controller (21) can be seen on the host computer (15) through a graphical user interface. 6. A method of optimization of a chemical leaching of coal in the bench scale unit as claimed in claim 1 comprising the steps of: Preparing the feed sample of fine clear coal after forth floatation process; feeding the feed sample either directly for next treatment of feeding crushed sample of 72 BS mesh size (-0.025 mm) that improves the kinetics of the process; treating the feed sample with varying concentration of 10-50% of dilute aqueous NaOH at varying temperatures under reflux with stirring for particular length of time varying from 1.5 to 7 hrs in the bench scale reactor; washing the treated coal repeatedly with water or HCL or with both; drying the washed coal; arranging the washed alkali treated coal to react with 10-20% H2S04 or HCL for 1-5 hrs and then the treated coal is filtered and washed with water and is sent for their chemical, rheological and petrographical properties. A BENCH SCALE UNIT WITH DATA ACQUISITION AND CONTROL SYSTEM FOR CHEMICAL LEACHING OF MINERALS AND A METHOD FOR THE SAME. A bench scale unit with data acquisition and control system for chemical leaching of minerals comprising of: - a batch reactor (11) with heating arrangement having a plurality of heating coils (26-29); - a condenser (12) with provision for reflux; - data acquisition and control system (13); - a host computer(15); - sparkler horizontal filter(16); - a stirrer (17) fixed inside the reactor (11); - a DC motor (14) to run the stirrer, and - a plurality of Resistance Temperature Detectors (RTD1, 2, 3) being positioned at bottom and 10cm and 20cm from the bottom of the reactor the bottom RTD1 being connected to PID controller (21) which controls the temperature inside the reactor.

Documents:

1391-KOL-2008-ABSTRACT 1.1.pdf

1391-kol-2008-abstract.pdf

1391-KOL-2008-AMANDED CLAIMS.pdf

1391-kol-2008-claims.pdf

1391-KOL-2008-CORRESPONDENCE 1.1.pdf

1391-KOL-2008-CORRESPONDENCE 1.2.pdf

1391-KOL-2008-CORRESPONDENCE-1.3.pdf

1391-kol-2008-correspondence.pdf

1391-KOL-2008-DESCRIPTION (COMPLETE) 1.1.pdf

1391-kol-2008-description (complete).pdf

1391-KOL-2008-DRAWINGS 1.1.pdf

1391-kol-2008-drawings.pdf

1391-KOL-2008-EXAMINATION REPORT REPLY RECIEVED.pdf

1391-KOL-2008-EXAMINATION REPORT.pdf

1391-KOL-2008-FORM 1-1.1.pdf

1391-KOL-2008-FORM 1-1.2.pdf

1391-kol-2008-form 1.pdf

1391-KOL-2008-FORM 13-1.1.pdf

1391-KOL-2008-FORM 13.pdf

1391-KOL-2008-FORM 18-1.1.pdf

1391-kol-2008-form 18.pdf

1391-KOL-2008-FORM 2-1.1.pdf

1391-kol-2008-form 2.pdf

1391-KOL-2008-FORM 3-1.1.pdf

1391-kol-2008-form 3.pdf

1391-KOL-2008-GPA-1.1.pdf

1391-kol-2008-gpa.pdf

1391-KOL-2008-GRANTED-ABSTRACT.pdf

1391-KOL-2008-GRANTED-CLAIMS.pdf

1391-KOL-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

1391-KOL-2008-GRANTED-DRAWINGS.pdf

1391-KOL-2008-GRANTED-FORM 1.pdf

1391-KOL-2008-GRANTED-FORM 2.pdf

1391-KOL-2008-GRANTED-SPECIFICATION.pdf

1391-KOL-2008-OTHERS-1.1.pdf

1391-KOL-2008-OTHERS.pdf

1391-KOL-2008-PETITION UNDER RULE 137.pdf

1391-KOL-2008-REPLY TO EXAMINATION REPORT.pdf

1391-kol-2008-specification.pdf

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