GB2150850A - A process for the underground purification of pit water - Google Patents

Abstract

Pit water is purified of solid contaminants in an underground purification process wherein abandoned mine roads ("macro-cavities") containing loose caved-in material ("micro-cavities") are utilised. The pit water is percolated by gravity through the macro- and/or micro-cavities, whereby it is purified by sedimentation and/or filtration.

Description

SPECIFICATION A process for the underground purification of pit water The invention concerns a process for the underground purification of mine effluents (pit water) by the removal therefrom of the solid particles, sediments and suspended matter content, expediently in association with winning by a caving method.

In the mining of solid materials water bursts or inrushes directly or indirectly connected with the production contain various kinds of solid particulate contaminants. Hence, these pit waters (mine effluents) cannot be directly utilised on their being raised from the mine either as industrial water or for agricultural purposes, and moreover, without pre vious purification they cannot be allowed to drain into natural waters. Because of their solid matter content, pumps raising them from the mine and which normally convey only pure water quickly become faulty. Thus, the whole water-raising system of the mine becomes damaged and inoperative for varying time periods and consequently very high material values may be endangered, especially when a water burst occurs.

To purify pit waters or effluents containing raw solid particulate silt and suspended material gener ally water roads, sedimenting and equalising sumps are included in the underground water-catching and water-raising system. In these sumps the high silt content of the pit water is settled out. Consequently, the sumps become full in a relatively short time. The full sump must be cleaned out by connecting in an exchange sump and the sump sludge or mud must be transported out of the mine and disposed on the surface.

The method is in general used notwithstanding the fact that when, as is normally the case, large amounts of water are present a very considerable amount of mining space is required, the establish ment and maintenance of which are very expensive and take up a considerable mineral wealth. However, the settling out process is not generally satisfactory.

A more modern solution is described in Hungarian Patent Specification No. 174,665 in which the settling out of the solid particles takes place in a sedimenta tion road consisting of a plurality of coaxial sections of essentially equal length. The raw pit water is introduced at the centre of the individual road sections where it is caused a flow at a velocity of 5-100 min/sec and is sedimented or settled out. The sedimented water is discharged at the two ends of the individual sections of the road and the thus formed mud or sludge is intermittently or con tinuously removed.

The process and the relatively complicated appar atus according to this prior invention are neverthe less of large dimensions and require mining spaces specially developed for the purpose, the sludge of which must be intermittently cleaned out and, as before, requires to be removed.

Mention has been made in the technical literature (A.A.Harionovsky -The Technological Methods of Purifying Pit Waters, Ugol Jan.192), of purifying pit waters by sementation and filtration with the aid of particulate materials. However, this method of purification may in practice be utilised only where the initial concentration of the contaminant materials is relatively low (100-150 mg. I).

The main requirements associated with the technological purification systems and plants for pit waters are summarised by the technical literature as follows: - The technological system for purification should provide a solution for the removal of the contaminants and for the handling, utilisation and storage of the sediment.

- The removal of the solid particulate material or silt should take place in one ortwo stages in dependence on their concentration in the water and their properties.

- The purification must assure the utilisability of the purified water either for industrial-agricultural purposes or for discharging into natural waters.

-The technological process of the water purification and the handling of the siltsludge should be reliable, economical, of simple construction and operation, should not tie down or take up large and useful areas and materials.

An aim of the invention is the elimination of the disadvantageous circumstances described above or at least their considerable or significant reduction; the invention also aims optimally to realise the general pit water purification requirements.

The task we accordingly set ourselves is the realisation of a pit water purification process which is simple and highly effective, while at the same time can be realised and operated with relatively little investment and labour costs. By using the process, the purification of the pit water to an appropriate level should be reliably and lastingly solved even under extreme circumstances, e.g. when a water burst or inrush occurs. As a further task, we set ourselves also the task of enabling the water purification process to be co-ordinated with the mining technology and of increasing the reliability of safety of the mining technology by its use.

We have discovered that the purification of pit waters arising from bursts or inrushes and containing significant quantities of silt and floating or suspended solid particulate materials can be solved by utilising mining spaces (such as roads and caved-in cavities) produced in the course of extracting solid minerals. These spaces or cavities are destined to be abandoned after their technological use. Such spaces may be roads of large extent and volume and can be regarded as macro-sized cavities, while the cavities formed in the cavings can be regarded as significantly smaller, micro-sized cavities; in these the sedimentation and filtration of pit waters can be extremely well solved with the aid only of gravitational percolation.As a result of the purification, the discharged water contains hardly any solid contaminants while at the same time, the large quantities of settled out or filtered out solid material which naturally is identical with the accompanying rock material, blocks or fills the macro-sized and micro-sized cavities whereby both the handling of the caving as well as the partial and complete blocking of the roads is also solved at the same time.

According to the present invention, there is provided a processforthe underground purification of pit water by removal of solid particles in the water, expediently associated with a caving-in mining method, wherein the pit water is conveyed to a section of the mining space(s) disposed at a relatively high level and caused to flow through a macrocavity or cavities and'or a micro-cavity or cavities of the mining space(s) by gravitation, while the silt or sediment and contaminated solid particulate matter content is removed by settling out and or filtration, then the purified water is collected and either raised from the mine water or utilised underground.

As macro-cavities, we utilise roads which have been left standing and were in any event destined to be abandoned, which roads may in advantageous cases be the entry andlor production roads of the winning. The propping of the lower-lying sections of such roads is strengthened, made more safe. The pit water is filtered in the micro-cavities of the caving. In a preferred embodiment the pit water is first introduced at the bottom of the mining space and the inflow position of the mine water is shifted in an upward direction. The purification of the pit water is performed in a pre-sedimentation step, a filtration step and a post-sedimentation step, or is carried out in one or more stages.

The advantages of the process according to the invention are listed below: (a) Pit water, especially when water bursts or inrushes occur, carries a relatively large amount of silt or other solid matter. If such pit water is not conveyed to a sump for settling out and purification but rather the sedimentation is carried out independently of the sumps in other mining spaces and, at the same time, by pasing the pitwaterthrough the caved-in mining space and its caving, the water is also filtered, then - the pit water is practically completely purified of solid particulate contaminants; - the caving of originally poorly filled cavities becomes more dense or solid;; -the macro-sized mining cavity is gradually completely filled by the solid matter that settles out which may allow a subsequent caving operation of the cavity to be obviated, and improves the packing of the caving.

(b) The caving which becomes more dense during the process is - of greater strength and is thus of better loadcarrying capacity, i.e. the convergence of the caving is reduced; - not porous, i.e. does not contain cavities, whereby its sealing or packing is better assured and thus the risk of outbreaks of endogenous fires is greatly reduced; - in the case of roof or hanging wall waters, it forms a relatively water-impermeable layer and thus promotes the directability of the flow of pit water.

(c) In carrying out the process in practice, the caving is packed or sealed and moreover this is done with a material which is most suitable for that purpose, that is with original rock material which: - is available at the site, - does not have to be found on the surface, usually a long way from the sludge pipe of the pit, does not have to be obtained and transported to the site and transported to a given mining cavity at great cost, power consumption and labour, where thereafter, especially during the sludging separate provision has to be made for the discharging of the water passing in and its purification by some suitable means.

(d) The process may be utilised immediately at the required site with practically no extra investment costs, since mining spaces are utilised which were in any case going to be given up or abandoned.

(e) The water gate and sump system of the mine is simplified, it may become shorter, since the sludge settling that is required to be performed at the sumps concerns only such solids-containing waters which cannot be involved in the process due to local properties.

(f) In given cases, the purification of especially high contaminated slurries or sludges originating from the cleaning of the sumps may also be effectively realised inside the mine by using the process according to the invention.

(g) The pit water raised from the mines is practically free of solid contaminants and thus - the service life and reliability of the discharge pumps are significantly increased; - the discharged pure water may be used directly, or with significantly less preparatory processing and further purification, for industrial.'agricultural purposes, or may be discharged directly into an ambient water system (brook reservoir) without risk of contamination.

(h) The operating costs, the associated material and labour requirements of the process are all low and the equipment (such as pumps, fittings and pipes) that may be required is that generally used in mining and may be generally and simply utilised.

(i) The process according to the invention may advantageously and with the usual or conventional means, be automated relatively cheaply and simply.

The process according to the invention and the results achievable thereby are described in detail by way of practical examples: Example 1 In a given mining area in which longwall mining is practised, between 50-90 1/mien, on average 70 llmin ground (pit) water occurred and the contamination bysiltofthiswaterwas measured to be 1.7 x 105 mail.

The contaminated water was transferred with a conventional slurry pump and a 100 mm diameter pipe to the air shaft of another, already exhausted and caved face wherein the pre-sedimentation of the water took place. From the air shaft the pit water passed by gravitation into the caving and after percolating through it was passed to the entry road.

The water was further purified by filtration in the caving and by post-sedimentation in the entry road.

No solid sediment or silt could be shown to be present in the water discharged from the process, while the suspended solid content was found to be 13.0 mail. During 85 hours of pumping operation, 1151/mien of pit water was delivered from which 44 m3 of solid particulate materials of 101.2 t weight was filtered out.

Example 2 Intermittently, at 10 minute intervals, the purity of the discharged water was monitored and recorded.

When the purity level exhibited a decrease of at least 20% between two consecutive measurements, the inlet of the contaminated mine water was placed at a position 0.5 m higher in the caving.

With this method the full thickness (3.4 m) of the face caving was utilised for filtration, a total of 7243.8 m3 pit water was delivered and a total of 853.7 m3 (1963.5t) solid particulate material was removed from the water. The major part (about 80-85%) of the material removed passed by filtering into the caving where it made the caving more dense, of greater strength and in practice completely airimpermeable. Of the smaller fraction, about 8-12% was removed from the water at the presedimentation stage and the residue in the postsedimentation stage.

Examples The process was also successfully utilised for purifying the sludgy slurry originating from sump cleaning. During 8 days of cleaning out a sedimentation sump, 2063.5 m3 slurry with a solid matter content of 11.14% was delivered to the purification system according to the invention.

In the course of purification, in round figures 230 m3 (529 t) solid material was removed from the highly contaminated slurry delivered to the system.

No solid material content could be shown in the discharge water, while the suspended matter content fell in the range of 16.0 -20.0 mail.

Claims (10)

1. A process for the underground purification of pit water by removal of solid particles in the water, expediently associated with a caving-in mining method, wherein the pit water is conveyed to a section of the mining space(s) disposed at a relatively high level and caused to flow through a macrocavity or cavities and/or a micro-cavity or cavities of the mining space(s) by gravitation, while the silt or sediment and contaminated solid particulate matter content is removed by settling out andlor filtration, then the purified water is collected and either raised from the mine water or utilised underground.

2. A process according to claim 1 wherein as micro-cavities, road(s) left standing and expediently destined to be abandoned are utilised.

3. A process according to claim 2, wherein as micro-cavity the entry and/or delivery road of the face is utilised.

4. A process according to claim 2 or 3, wherein the proppping of the lower-lying section of the road is strengthened.

5. A process according to claim 1 wherein the pit water is filtered in the micro-cavities of the face caving.

6. A process according to claim 1, wherein the pit water is introduced into the bottom of the mining space.

7. A process according to claim 6, wherein the position of introduction of the pit water is shifted intermittently in an upward direction.

8. A process according to claim 1 wherein the purification of the pit water is performed in presedimentation, filtration and post-sedimentation steps.

9. A process according to claim 8, wherein the purification is performed in one or several stages.

10. A process for the underground purification of pit water substantially as herein described with reference to any one of the Examples.