1. Current Technologies for Raw Material Quality Control.
1.1. Computer Aided Technology for Generation of Mathematical Model Simulating a Complex Structure Deposit and for its Reserves Calculating.
1.2. Computer Technologies for Generating, Based on the Reserves Model, of Optimal Final Shape for an Open Pit and Its Development Schedule.
1.3. Automated Control System for Vehicle Routing inside an Open Pit (ACS VROP) .
1.4. Automated System for Mined Ore Quality Control (AS MOQC).
1.5. Preliminary ore beneficiation by sorting.
 1. Current Technologies for Raw Material Quality Control. |
The experience in designing, construction and operation of open pits shows that cost efficiency of mining facility in many respects depends on the proper construction decision, selection of the technology and mining mode, calendar distribution of overburden and ore volumes as well as type of comprehensive mechanization of production processes.
To optimize development of mining facilities we have designed and have been using the special computer aided technologies for generation of mathematical model simulating a deposit, optimal final shape of an open pit and its development schedule, raw material quality control and mined ore flow control systems as well as computer aided complex for preliminary upgrading of ore by means of sorting. Computer technologies have been designed and put into operation at Navoi Mining & Metallurgy Combinat (NMMC) by INTEGRA GROUP Ltd (USA) and INTEGRA Closed Joint-Stock Company (Russia) Companies with participation of Uzbek specialists and they continue to do this now.
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 1.1. Computer Aided Technology for Generation of Mathematical Model Simulating a Complex Structure Deposit and for its Reserves Calculating. |
There are very few computer aided technologies used for generation of a deposit model and its reserves assessment in world practice of mining companies. The common approach to this problem includes dividing of the total volume of the deposit into the cells - parallelepipeds of similar (or different) size and calculating of an average grade in each of them by one of interpolation methods (so called "Cricking"). Then those cells in which that grade is higher than cutoff grade are combined into groups according to ore types; their total volume, average metal concentration, tonnage and etc. are calculated. At that process each cell of the model (as well as combination of all "ore" cells) is considered like a block of mining mass with 100% coefficient of mineralization continuity. Then it is assumed that after a network of operational sampling wells has been drilled in that block (in our case - network of Drilling-Explosion Works) and selective mining has been done, individual lens of waste rock, sub-economic ore and etc. will not be successfully found. Using common terminology it is possible to say that given method results in significant dilution of ore and ore losses in entrails of the earth. As a consequence, evaluations of deposit reserves obtained as a result of such computer calculation quite often differ from conventional ones and have lower metal concentration in ore and higher ore volume and metal tonnage.
Developed by us new computer aided technology for generation of mathematical model simulating a deposit and for calculating its reserves has no the above disadvantages and briefly could be described as follows.
According to geostatistics canons the deposit could be presented as a set of points (field). The certain distribution of probabilities of detection of different metal concentration values is determined in each set. It is usually believed that the above set (field) consists of two kinds of fields (or of two components): the first one gradually (slowly) changes in space, reflecting the general trends of concentrations increasing or decreasing; the second one quickly changes in space, reflecting local fluctuations of concentrations. In contrast to conventional approach the first component is considered to be a random field, values of which are not the figures but functions of values distributions (bar chart) of quickly changing field (second component). Not describing the details we note that proposed method is a method of relative distribution determination and it is remarkable for its non-parametric model and it allows working with distributions of non-standard type which are typical for actual distribution of precious and rare metals.
Actual average concentration in each bar chart gradation is calculated by means of averaging out of the average concentrations in relevant gradation of summable bar charts with weighs proportionate to interpolation coefficient and their relative frequencies.
The sum (with weighs) of three correlative functions with correlation radiuses which are equal to correspondingly doubled bench height, average distance between wells in profile and average distance between exploratory profiles was taken as a spatial correlative function for bar chart cricking.
Making bar charts of concentrations in samples (or intervals) we determine reserves (total or per separate areas) corresponding to that selectivity level which is reachable using selected sampling network and method of sampling. In that case it is an exploratory wells network. Actually selectivity of a pit development (excavation) is determined by the step of operational sampling network. For example, selectivity of a pit development at Muruntau gold deposit corresponds to excavation volumes whose height is equal to excavation bench and in plan it is a 5.5m x 5.6m cell (mesh). Besides, in comparison of the detailed exploration results with operational exploration data, difference between wells diameters and corresponding sample volume should be taken into account. Concentrations in larger volumes are obtained by averaging of concentrations in smaller volumes included into larger ones.
Reserves evaluation in any volume composed of model cells or at the deposit as a whole is made based on bar charts which have been plotted for each of the model cells. For the prescribed cutoff grade the sum of probabilities of grades exceeding cutoff grade is interpreted as coefficient of the cell mineralization continuity.
Ore and metal reserves in a given volume are calculated as a sum of reserves in model cells included into that volume. Average volume grade is calculated as a ratio of metal reserves to ore reserves.
The principal distinctive feature of the proposed model is the usage of probability distribution function as an interpolation subject and as a characteristic of each cell of the given model. All previously known technologies for such models generation operate with determination of the average metal concrntration while our method is based on operations with function describing probability of appearance of different values of concentrations in a given volume. In such case the concentration becomes only a fragment of the proposed model.
All the previously proposed technologies make it possible to obtain determination of the average metal concentration in the whole volume of the elementary model cell. Technology offered by us gives the average ore grade determination obtained under the certain cutoff grade. In this process it is also determined what portion of the cell volume will be occupied by the mentioned ore mass.
The new conception has been introduced by us, namely -operator of a model conversion in the process of transition from one type of sampling to another and changing of parameters of the sampling network. It allows making the universal model and its use for transition from geological to operational reserves obtained in realisation of different networks of technological wells with different diameters.
Based on the above computer aided technology mathematical model of Muruntau Deposit was generated for the first time and computer aided multichoice calculation of its reserves was made.
Results of well sampling and excavation in the process of exploratory works were used as a data base (totally 585.5 thousand samples).
Altogether 48 versions of the reserves calculation were processed.
For the purpose of the model verification and reserves calculation with it, comparison of the model reserves with operational exploration data on the suite of previously excavated areas (sites), in several horizons and in various parts of ore beds was made. Sites for comparison were being selected in such way that deposit volume could be represented in full possible measure.
Results of comparison between summary reserves assessments on all explored sites for different cutoff grades and the results of excavation have shown a good precision.
Given that total volume of compared reserves on the sites of Muruntau Deposit exceeds 400 ton of gold, it could be considered as well proved that: use of mathematical model for the reserves calculation allows 2-2.5 times decrease of systematic error taken place in general reserves calculation in 1985. At the same time relative error in the reserves evaluation obtained using our model decreased in comparison with such error in general reserves calculation (for 1.0 g/t cutoff grade) as follows:
- for ore - from 20.7% to 9.5%;
- for metal - from 23.2% to 14.8%.
Thus as a result of performed job the more reliable evaluation of raw material base of the Deposit was obtained and it was used for designing of the stage IV of Muruntau open pit.
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| 1.2. Computer Technologies for Generating, Based on the Reserves Model, of Optimal Final Shape for an Open Pit and Its Development Schedule. |
One of the most important and determinative problems of the open pit designing is a determination of the open pit borders (limits) in its final position (so called "shape for an open pit"), its production output, system of development mining and schedule of its development (including delimitation of mining per each year). Full recovery of mineral wealth from the depths of the earth, open pit construction and operation costs and finally basic performance characteristics of the design depend on the above issues effective decision.
Final shape for an open pit is typically determined from several sections (usually - transversely to course of ore bed), in each of them such open pit section is located in which contour stripping ratio reaches value of boundary coefficient. The latter is determined based on the ratio of a benefit from a sell of "additional" products to stripping cost. The present method (so called "method of boundary stripping ratio" or "method of addition") has some significant disadvantages, the main of which consists in such fact that metal concentration in each "addition" is usually equated with average concentration in section (or even throughout the ore bed). The obtained results are respectively enough rough and the final shape for the open pit designed by such method is far from optimum.
Development schedule of the open pit, its system of stripping and other subsequent problems, connected with determination of the final shape for an open pit, are also have respective deviation from optimum (errors).
During the last decade in practice of mining companies all over the world computer aided methods based on Lerch-Grossman algorithm have been used for the purpose of an open pit designing. However their realisation in designing of such a large open pit like Muruntau mine is not possible without super-speed computer. It in its turn requires large investments, foundation of special departments and etc.. The above difficulties induced us to find our own decision for development of such computer aided technologies based on conventional computers. We have decided such problems in great extent and successfully used them in correction of the design of Muruntau open pit (stage III) and currently we have been applying them in Feasibility Study for stage IV and for other facilities.
In contrast to Lerch-Grossman algorithm our algorithms have a rapid algorithm convergence, i.e. they do not require full enumeration of all possibilities of the decisions. Theoretical grounds of the applied algorithms and their brief description as well as description of the computer aided technology based on them and results of its use in practical designing and construction of Muruntau open pit are given below.
Boundaries of an open pit mining (final shape) - we have been solving this problem using heuristic algorithm, realising so called "method of mobile cone". In accordance with mathematical model of the deposit the latter can be represented as a totality of elementary blocks (cubs or parallelepipeds) of a given size, in each of which ore and metal reserves have been evaluated under a given cutoff grade.
It is known from the deposit model data that under fixed cutoff grade the certain quantities of ore and metal are contained in a given block. Taking into account accepted values of losses and dilution as well as
through (start-to-finish) recovery ratio, quantity of the metal, obtained in case of rock excavation and ore processing, is determined. At that, summary cost of excavation, transportation and ore processing together with corresponding taxes are considered. If gold price is known it is possible to determine the benefit from mining of the given ore block and processing of the ore contained in it.
It is known that any block excavation in open pit mining requires excavation of all other elementary blocks, located above it and inside the certain cone, which shape depends on accepted angles of a pit edges slope in their final position. It is clear that blocks located at a higher hypsometric level subject to earlier excavation than lower blocks. Thus in general case a portion of blocks in cone will also belong to other cones which bottom is located above and in the neighbourhood with a given block.
Looking over all elementary blocks profitable for mining (under accepted prices) in each horizon in direction of their hypsometric level increase, we can find a lot of blocks with a profit "higher zero".
According to profit criterion this set of blocks represents a block model for an optimal final shape for an open pit because in this set all profitable blocks are combined and blocks with negative profit are excluded.
It is possible to imagine such model of a deposit in which no one block has profit (for instance, enough deeply lying tabular ore body) but combination of such blocks gives a positive effect (profit). Thus our algorithm provides for heuristic methods of blocks combination which allows excluding of the above error.
Optimized schedule of an open pit development - is of critical importance for design of mining work (like as a final shape).
Calculation of an optimal schedule of an open pit development is the most important and difficult problem in designing of an open type mine. Here the economical problem of investment distribution conflicts with a complex system of technological restrictions. Economical factors require the soonest recoupment of capital investment, so large stripping costs are required to be paid in a later period but estimated level of mined ore volume and final product output are required to be reached as soon as possible.
At the same time technological factors require timely development mining of the reserves, construction of transport roads, usage of limits of speed of a pit edge lowering. Optimal solving of that contradiction considering specific features of metal location in ore and technological properties of the ore in deposit can be reached only using the highest modern calculating methods and equipment.
The proposed computer technology is realised based on the new methods of complex dynamic process control. Decision is optimised according to maximum profit criterion under a given credit interest and considers all technology restrictions including prescribed angles of a pit edges slope, maximum allowed speed of a pit face lowering, requirements of transport system, prescribed output capacity of enrichment and metallurgy facilities. These restrictions (especially concerning the speed of a pit lowering) have never been considered by any other known technologies for formation of the schedule of an open pit development (DATAMINE, WITTLE-4D and etc.).
The problem is solved by iterative use of the above algorithm for forming of the final shape for an open pit, this shape firstly is calculated for the first year of a pit development, then for the second one, the third one and etc..
Let us imagine these shapes as combinations of elementary blocks. Their set can be considered as an annual-base schedule of mining works taking into account the mining realisation profit.
Profit related to the present period profit (coerced) is determined considering summary profit and discount coefficient.
From all possible schedules of a pit development we are interested in that one which has maximum coerced profit.
Given problem is solved by iterative use of the above algorithm for forming of the final shape for an open pit, this shape is calculated under different product prices (gold price in our case).
In fact it is seen from the above that volume of the final pit shape is a non-decreasing function of gold price. Assuming that gold prices (per one gram) form a row, it is possible to form for each price its own final shape as a function of the price. At the same time these shapes also form a row in which every subsequent shape includes all previous functions.
It should be noted that at the same gold price (for instance, conforming to its real cost) specific profit (per product unit) is decreasing for the elements of the row of elementary block combinations.
Having obtained the sequence including sufficient quantity of the optimal final shapes we can combine them into annual groups depending on the price per each year where each pit shape conforms to a pit boundaries by the end of each year. Combinations are made to meet the following requirements:
·quantity of ore and metal mined in the process of a pit development in each year should be in accordance with plan values;
·lowering of a pit bottom and edges during the year should not exceed prescribed value.
The latter problem is being solved by the method of dynamic programming.
It is possible to say that the pit shapes formed according to the above description reflect the near optimal schedule of the pit development because:
· summary coerced profit from the total schedule realisation corresponds to the condition characterising maximally coerced profit;
· in realisation of the given schedule the basic technological restrictions (connected with a speed of lowering of a pit bottom and edges, angles of a pit edges in their final and operational position and etc.) are observed.
The above mentioned algorithms for determination of a pit final shape and its development schedule are the base of the computer aided technologies included into Computer-Aided Design System for Mining Works (CADS MW) at Navoi Mining & Metallurgy Combinat (NMMC) as well as in some cases they are used independently.
Input data are as follows:
·Price forecast (or price dynamic) for a final product and interest on credits;
· Costs of basic works: excavation, transportation of ore and mined mass, ore processing and etc.;
· Basic technological performances: coefficients of losses and dilution, through ratio of gold recovery (for different types of ores), angles of a pit edges in operational and final position, berms width, maximum speed of lowering of a pit bottom and edges and etc.;
· Mathematical model of the deposit and relief.
The result of the problem decision is the optimal final shape for an open pit shown in isolines as well as the schedule of an open pit development with graphic presentation of all intermediate shapes and with results of calculations of mined mass volume, weight and grade of mined ore, concentrations of minerals in ore and relevant economic indicators.
| Using this technology we can compare the development schedules for various versions of ore and metal production output and choose such optimal output level that provides the best economic performances and at the same time ensures timely advanced development of stripping works. The technology makes it possible to model various options of a pit development, forecast crisis situations, connected with backlog of stripping work in comparison with mining work, and avoid them.
The above mentioned technologies of construction of the optimal final shape and development schedule for an open pit for the first time have been realised at Muruntau open pit.
Let us briefly consider the results of the above technologies application in a practice of Muruntau open pit construction. For the first time these technologies were used there in 1989-1990 in correction of mining works design for the Stage III of the open pit. Expertise carried out by All-Russian Scientific Research Institute for Industrial Technologies Designing showed that:
· 15% decrease of stripping volume was reached without substantial reduction of total ore and metal reserves;
· development schedule of Muruntau open pit Stage IV was significantly changed.
According to the new schedule the open pit decreased annual volume of stripped mined mass from 40-42 to 32-35 million m3, postponing essential portion of stripping works till the later years of a pit development.
Besides volumes of stripped rocks decreased substantially (by 30%) at the same level of recoverable reserves.
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1.3. Automated Control System for Vehicle Routing inside an Open Pit
(ACS VROP) . |
The system functions based on GPS navigation system and makes it possible, in real time, to determine position of every mobile or stationary subject using radio signals from communication satellite.
The technology was developed in the U.S.A. in 1980-1990 and currently it is widely used. There are some approaches in achievement of more data accuracy and integrity as well as GPS system capacity increase.
With reference to ACS VROP the essence of our method consists in use of a base station with accurate position data which are periodically compared with position data measured using GPS-receiver by means of data accumulating and averaging. Difference between measured and accurate position data is called "differential correction" which is transmitted to mobile GPS and used for correction of the measured position data. After the above measurement, made by mobile GPS, the position data are transmitted to the computer via radio modem (or in other way). Installing such receivers at the mobile subjects (trucks - in our case) and properly processing data, transmitted from them to the computer, it is possible to display positions of trucks in a selected co-ordinates on the road map and etc.. Having obtained such information, it is possible to monitor mobile subjects (trucks), perform their production control and solve problems with their optimal distribution. The above description is a general concept of GPS use in ACS VROP.
Structural scheme of ACS VROP includes the following basic components:
A) Subsystem of Mobile Positioning (SMP) of mining equipment, consisting of separate mobile blocks (installed on each unit of the equipment). Each such block includes GPS-receiver, radio modem and radio station commuted with each other. SMP is designed for periodical measurement of the equipment position data and their transmission to the traffic superintendent station as well as for receiving of traffic superintendent commands by the drivers. Each of the SMP mobile blocks is being programmed for the purpose of higher accuracy of position data measurement considering relief details. Radio station capacity is determined taking into account radio-waves propagation conditions. Radio station is equipped with a block of voice communication with traffic superintendent station. Voice messages and data are transmitted in the same frequency without interference.
B) Subsystem of Production Control (SPD) is designed for optimisation of interaction between transporting and loading equipment. The following components are included into the Subsystem:
· base GPS;
· station determining the above differential correction;
· block of digital receivers and radio modems designed for data receiving from mobile sets and data input into computer, as well as central server and several computers for processing of messages from SMP. Each of these messages includes the following information about the certain truck:
· truck number;
· truck position data at the present moment;
· speed of its movement;
· direction of movement.
Messages are transmitted from each SMP with interval 20 seconds, then they are set into server file and processed by means of programs combined into software subsystem.
All SPD computers are connected by telecommunication lines with a main (central) server which allows more effective vehicles control.
C) Software Subsystem (SS) is designed for optimisation vehicle routes, accounting of mined mass transported from excavator to a stockpile, graphical presentation of current information (against a pit map background) on the screen of a display, voice communication and obtained data input and saving in a data base.
It should be noted that ACS VROP at Muruntau open pit showed its high efficiency already in the first months of its operation. For the first time we have got the opportunity to actually control each truck position, optimally re-distributing their routes in case of changing situation in operation of truck-excavator complex (excavator, crushing - loading stations are out of operation and etc.). Preliminary assessments show that the system allows significant increase (8 - 10%) of the effectiveness of the vehicle and excavator complex operation at the mine.
As a conclusion it should be noted that:
ACS VROP together with its software and hardware interacts with Computer-Aided Design System for Mining Works (CADS MW) and with Automated System for Ore Quality Control (AS OQC). Thus equipment position and movement data and mined ore quantities information are transmitted to the server in a form acceptable for use in CADS MW programs. On the other side information from some CADS MW subsystems (grade plan, surveyor data, drilling plan and etc.) is transmitted to AS OQC and then to ACS VROP. In future CADS MW is supposed to integrate with other mentioned systems and develop united system for the open pit control.
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| 1.4. Automated System for Mined Ore Quality Control (AS MOQC). |
In spite of significant efficiency of the developed systems the problem of selective mining is still actual. First of all it is connected with the fact that ore mining is performed according to surveying rods which are installed in the natural conditions of a stope along defined contours after ore block explosion. To decrease impact of this negative factor as much as possible we developed automated system for mined ore quality control (at Muruntau open pit) using the above mentioned GSP cosmic navigation system. Position data (x,y) of excavator bucket horizontal plane projection are determined by means of GSP-receiver with high accuracy (up to 1m). Position point (x,y) is projected on the screen of vehicle-borne computer (installed in an excavator driver's cab) on which block (where the excavator works) mining plan according ore grade is displayed. Thus excavator operator not observing surveying rods locations can easily orient himself at the plan and at any time know ore grade loaded into truck. The same position data (x,y) at the moment of bucket loading are transmitted to the central computer where evaluation of gold concentration in the loaded bucket and then - in the truck is calculated using algorithm of non-linear interpolation of sampling data from the nearest drilling-explosion wells (see description of "Ore" Automated System algorithm). Depending on this evaluation the truck is sent to the certain stockpile and computer monitors if the ore is delivered properly to the determined stockpile.
The general structure of AS MOQC includes five following subsystems: data base, quality control of ore mined in an open pit, monitoring of recovery contours observance in the process of excavator work, pit face sorting, quality control of ore mined in a face.
Data base accumulates the following information necessary for the System functioning: on-line month plan of mining works; mine surveying data (face position, position data for drilling-explosion works and etc.); plans of mining in accordance with ore grade in blocks excavated in current month; contours of each excavator stoping (information is accumulated in real time, then is integrated and erased); table of results of a face ore sorting (for each excavator and truck); hourly schedule of mined ore quality (for each excavator and for open pit as a whole); other reference data.
Quality control of ore mined in an open pit. This subsystem performs
- recording of the results of ore loading from each excavator, from the sites (summary data from excavators), from an open pit as a whole (quality and quantity of the ore loaded during one hour);
- accounting of the above results with progressive total and comparison of the actual performances schedule with the schedule in on-line plan of mining works;
- forecast of anticipated dynamic of the ore flow performances;
- in case of difference between the plan and actual data it gives recommendations concerning correction of mining works development at the separate sites and faces of an open pit.
Monitoring of recovery contours observance. This is a distributed subsystem and it is realised at each excavator in ore face. It is based on the method of ore flow quality control including selective ore extraction per contours as well as distribution and addressing of the trucks with different ores. Subsystem consists of three important procedures:
· Procedure of determination of (x,y) position data (by means of GPS equipment), subvertical line through the face along which excavator bucket moves in the moment of its loading with ore mass;
· Procedure of the results visualisation at the screen of the excavator-borne computer display where position of the bucket at the moment of loading and excavator stope plan are displayed;
· Procedure of data transmission to "Quality control of ore mined in a face" subsystem.
On the manager demand, figures of excavator work per shift showing quantity and quality of the loaded ore are displayed at the video monitors of control stations in exit trenches and central control stations.
Pit face sorting. This subsystem has been registered as an invention. It is designed for sorting of the ore from each truck directly in a face. It is based on mathematical treatment of sampling data. Special programs solve this task. Input data are as follows: (x,y) position data of the horizontal projection of the excavator bucket movement at the moment of its loading with ore mass (see above) as well as (x,y) position data of drilling-explosion wells located around this point at radial distance 50m. Evaluation of metal concentration is made for each excavator bucket and then summed according to quantity of buckets for a given truck. The obtained figure is a final result of this procedure.
Quality control of ore mined in a face. Having received determination of the ore grade the subsystem makes a decision concerning truck addressing which is displayed for excavator operator, for a truck driver and at the central control station of an open pit. Besides, records on loaded ore per each truck are made as well as comparison between plan and actual quantities of the mined ore.
As a whole, functional layout of AS MOQC represents the following structure:
"Monitoring of recovery contours observance" Subsystem is a main body of the System. It determines (x,y) position data for a bucket and visualises its position at excavator stope plan. Then the bucket movement line position data enter into "Pit face sorting" Subsystem that transmits information on metal concentration and technological type of the ore loaded into each truck into "Quality control of ore mined in a face" Subsystem. Elements of the subsystem are realised on each excavator. The subsystem makes decision on each truck addressing, excavator stope boundaries and periodically transmits these data into "Quality control of ore mined in an open pit" Subsystem and into the Data Base. Analysis of the ore flow conditions per each mining site and for the open pit as a whole, comparison between on-line plan of mining works and actual data about the ore flow and respective corrections are carried out in the Subsystem. Then information is transmitted into the Data Base and archived. Periodically (quarterly) as well as on demand the conditions and results of mining works are analysed, dynamic of actual performances is compared with on-line plan performances, forecast for mining development as well as recommendations regarding on-line plan corrections and mining equipment distribution per sites and etc. are given.
It should be noted that according to preliminary evaluations AS MOQC allows:
· waste rock sorting resulting in 2-3% losses decrease, 5-6% dilution reduction and therefore ≈1-3% mined ore grade increase.
· 10-15% increase of economic ore (more 2g/t) output owing to its mining from sub-economic blocks.
· 10-15% increase of sub-economic ore ( 1.5-2g/t) output from blocks of mineralised mass.
· 1-15% increase of mineralised mass output from blocks of internal stripping.
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| 1.5. Preliminary ore benefication by sorting. |
Technology for preliminary upgrading of sulphide gold ores (the patent holder is INTEGRA GROUP Ltd. , USA) accepted by NMMC for commercial use provides for X-ray - radiometric separators usage that are designed by the same company.
System of fundamentally new methods, devices and software is realized in these separators which makes it possible to improve technological performances of pre-upgrading.
The basic features of them are as follows:
- Usage of automated system of continuos dosed supply for a stable material discharge from separator feed bin and material feeding into technological cycle. This system allows stable formation of mono-layer at a vibrating feeder of separator feed bin which in its turn promotes stable on-line mode of ore particles (pieces) location at the vibrating feeder.
- Usage of special design of vibrating pickup with stable flow of particles of different shape which provides stable on-line mode (particles move in a single row (abreast) tightly one after another) of their location at the chute of vibrating pickup. Speed of particles movement in the chute of vibrating pickup at the moment of their relocation on the belt of separator can be adjusted from 0.5 to 1m/sec. due to change of the chute slope angle and mode of vibrator operation.
- Usage in detection blocks of proportional counters with special filler which makes it possible to decrease efficiency of registration in the area of singly diffused radiation by an order of its magnitude. As a result of it, in Irradiating - Measuring Devices (IMD) of such separators it became possible to apply powerful X-ray generators under acceptable loads per counter. Owing to that the sensitivity threshold in determination of classification criterion increased by several times, which allows twice increasing of separator capacity without deterioration of technological separation efficiency.
- Usage in IMD of collimators with narrow slot for primary x-ray irradiation and "zero" probe makes it possible to practically completely exclude "highlight" effect (influence of neighbour particles), essentially improve selectivity of irradiation processes and registration of secondary irradiation of pieces. The most important thing is the use of original design of IMD in X-ray - radiometric separators which made it possible to practically completely eliminate impact of changeable particle sizes and their movement trajectory on the separator belt on the results of classification criterion determination.
- Achieved high selectivity of irradiation and registration processes allows effective operation of "gamma-screen" for detection of the moments of particle entering into measurement zone and their leaving when the space between particles on the conveyor belt is 2-3cm. Owing to that it became possible to realize single particle mode in practically solid stream of particles on separator belt which increased separation output by 30-50%.
- Continuous in-line arrangement of several IMD along the trajectory of particles movement allowed realizing of their "many-sided vision" which in its turn highly increased representativity of classification criterion determination and thus notably improved technological efficiency of preliminary upgrading especially for ores with a threaded type of mineralization.
- Usage of a conveyor belt made of a special composition made it possible to improve characteristics (spectrum) of the secondary x-ray irradiation and thus decrease error in classification criterion determination.
- Automated external voltage and current control in anode of x-ray tube as well as set values monitoring using serial interface with high level computer (Automated Separator Control) made it possible to keep instability of flux of primary x-ray irradiation less than 1%.
- Usage of complex separation features (criteria) for ore separation. Based on the results of simultaneous determination of several metal concentrations (measurements in several spectral regions of secondary x-ray irradiation) complex classification criterion is calculated as an analytical formula realized by programs in measuring-control system of separator. Firstly the system determines technological ore type and then within the frames of each type it classifies particles as ore-bearing or barren ones.
- Maintenance of stable prescribed gold concentration in separation tailings regardless of gold concentration in the original (feed) ore. Researches of INTEGRA specialists show that to maintain prescribed gold concentration in separation tailings it is necessary to change limiting value of classification criterion (separation threshold) depending on gold concentration in the feed ore. Otherwise under fixed non-flexible separation threshold (for example, separation threshold is set as an optimal one for economic ore separation) it will inevitably result in increase of gold concentration in tailings when gold concentration increases in the feed ore delivered for separation which will cause unjustified gold losses. And vice versa, adjustment of separation threshold for high grade ore separation will result in decrease of tailing output for sub-economic ore, i.e. decrease of the efficiency of preliminary ore upgrading.
Usage of the technology of preliminary ore upgrading makes it possible to:
· significantly improve quality of the feed ore delivered for hydro-metallurgical processing at the plant (≈ twice increase of gold concentration);
· involve additional gold quantity into processing owing to extraction from base and economic ore of high grade ore type which is the most efficiently for this process.
Simultaneously with introduction of benefication of sulphide gold ore Navoi Mining develops a complex of research works aimed to upgrade Muruntau type of ore containing "free" gold. Examples of sorting based on indirect features of this ore type have not been known anywhere in the world. Though, we managed to find positive solution for this problem.
Finally it should be noted that Navoi Mining is planning to combine CADS MW, AS MOQC, ACS VROP and preliminary ore upgrading into Integrated Mining Works Control System with a common Data Base and data communication through the common server. |
