GB2094854A - Dredging - Google Patents

Abstract

Process for the excavation of sands containing mineral wealth, in the region of a river bed, and for simultaneously improving the infrastructure in the landscape. A floating dredger with a treatment installation for the excavated sand is guided upstream and the waste which occurs after the treatment for recovery of mineral from the sand is used for damming the river behind the dredger and embanking the dredged river. <IMAGE>

Description

SPECIFICATION Process for the excavation of sands containing mineral wealth The invention relates to a process for the excavation of sands containing mineral wealth, in the region of a river bed, and for simultaneously improving the infrastructure in the landscape, by the use of a dredger.

There are, on earth, numerous rivers the sands of which contain mineral wealth, for example placer gold (alluvial gold). Such sands containing mineral wealth are mostly excavated by means of conventional heavy-duty land-bound dredgers, as known from civil engineering. The excavated sand is further treated in separating plants which are operated, independently of the dredgers, at some distance from the area of excavation. Gold-bearing sands can, for example, be washed with water in washing installations, in order to separate the precious metal of high specific gravity from the sand.

This excavation process presupposes a developed infrastructure in the region of the area of excavation. Before the actual excavation, earthmoving and transport work must first be carried out to a relatively large extent, in order to set up the separating plant. The excavation of the river sand itself then necessitates the movement of large masses of sand and waste overland. All this can be mastered only by means of considerable investment with the use of the most modern techniques. Consequently, the land-bound excavation of river sands on a commercial scale is practised almost exclusively in the territory of the large industrial nations. Unfortunately, this action frequently leaves behind; as a consequence, a destroyed landscape and gigantic waste tips.

On the other hand, there are, throughout the world, numerous smaller rivers, the sands of which cannot be excavated by means of the processes according to the state of the art. In this case, excavation from the land on a commercial scale can be confronted with geographical and climatic difficulties and problems of infrastructure.

Particularly in tropical regions, for example in West Africa, attempts have been made in vain for decades to excavate the sands of river banks by means of heavy-duty machines according to the known method. This has been frustrated, on the one hand, by the narrowness of the river valleys, which greatly hampers the use of large pieces of equipment, and, on the other hand, by the enormous quantities of water which flow down in the rainy season and which make land-bound machines practically incapable of moving in the region of the river courses. Thus, even today, mineral wealth is still extracted, in these areas, mostly by hand with very small implements.

The object of the invention is to provide a process for the excavation of sands containing mineral wealth, in the region of a river bed, and for simultaneously improving the infrastructure in the landscape, by the use of a dredger, which process enables mineral wealth to be extracted on a commercial scale, without large demands on the technology of the surrounding land, under difficult geographical and climatic conditions.

This object is achieved, in a process of the type mentioned in the introduction, due to the fact that a floating dredger is guided upstream and, in so doing, sand is excavated, this sand is graded and washed on the dredger and the waste is conveyed by a discharge unit, for simultaneously damming the river water and building dammed stages, and is deposited to the side and/or downstream.

Advantageous developments of the process and a floating dredger for carrying this out are characterised in further claims.

A great advantage of the process according to the invention in comparison with the state of the art is the excavation, from the direction of the river, of the sands containing mineral wealth. In this, the floating dredger can move on the water independently of the particular structure of the banks It carries with it the separating plant for extracting the mineral wealth and discharges the waste which occurs directly and in an intended direction. Operating the dredger together with the separating plant on the river itself makes no large demands as regards the level of technical development of the surrounding area. Even climatic influences can be only slightly prejudicial to carrying out the process.Consequently, a preferred application is found in those areas which have hitherto been closed to the excavation on a commercial scale of sands containing mineral wealth in the region of river courses. In contrast to the case of known processes, an area with a beneficial and efficient infrastructure is left behind after the excavation of this mineral wealth.

According to the invention, the sands containing mineral wealth are excavated by means of a floating dredger, starting from the mouth of the river in an upstream direction. The sands are treated on the dredger itself. The waste which occurs is discharged directly from the dredger via controllable conveyor devices. When this is done, a part of the waste can be used to build retaining dams transversely through the excavated river bed. Thus, the dredger moves on self-made dammed stages. With other quantities of waste, dams are accumulated and causeways built to the side of the excavated river bed. To.carry out this process, it is absolutely necessary to effect the excavation in an upstream direction.

Sands containing mineral wealth are found in an environment of river courses, the extent of which often exceeds many times the river bed which exists at the present time. According to its origin, the gravel layer bearing the mineral wealth may easily be approximately 30 times wider than the water surface. Before the dredger begins its activity, the growth present on the surface to be excavated, as well as the humus soil, can, if appropriate, be removed in a conventional way.

The humus soil is advantageously used again later for ground cover.

The process according to the invention can even be used in the case of a river width of only a few metres and a water depth in the dry season of, for example, only 30 cm. For this purpose, before the start of the operation, the river bed is widened and deepened at a point in the lower course with a dredger of conventional design. The basin produced in this way must be a few metres longer and wider than the dimensions of the complete floating dredger. As soon as the basin has been filled with water, the floating dredger is placed therein.

The floating dredger then starts to operate in an upstream direction. Sand containing mineral wealth is excavated and delivered to separating plants which are located on the dredger itself. The waste which occurs during the separation is under control from the dredger -- deposited behind the dredger and to the side of the length of river to be excavated, in such a way that dams, between which the arriving river water is dammed up, are obtained. Since the rivers containing mineral wealth are mostly situated in inaccessible regions, it is appropriate to dump a part of the waste to form a causeway running parailel to the excavation length.

After the floating dredger has excavated an appropriate section of length upstream, the water depth always becomes smaller - in dependence on the descent of the river. Before the floating bodies of the dredger make contact with the river bottom, a new dam is built up downstream behind the dredger, transversely through the excavated river bed, so that a new dammed stage with a greater water depth is obtained. When the floating dredger has, in this way, reached an area in the region of the river source, where the local conditions make the dredger practically incapable of moving, it is dismantled into appropriate parts and transported away on the causeway obtained, so that it can be used again in another area.

A floating dredger developed for carrying out the process according to the invention is illustrated in the Figure. This shows diagrammatically a section through a river bed in which the floating dredger is working. The slope, illustrated in the background (on the left) of the Figure, of the riverbank 1 descends to the surface 2 of a water layer 3 which is very flat in accordance with the upper course of a small river.

The bed of the river is formed by a layer of coarse shingle 4 which covers the gravel layer 5 containing mineral wealth. Beneath this gravel layer 5 lies a sand layer 6 which contains no mineral wealth or only negligible mineral wealth.

The floating dredger is mounted on floating bodies or pontoons 7 which are designed with an extremely small draught. The draught should be set between 50 cm and 80 cm in the case of a full load. Located on the floating bodies 7 are a winning unit 8, a treatment unit 9 and a discharge unit 10 which serves to convey and deposit waste 11.

In the exemplary embodiment illustrated, the winning unit 8 consists of a vertically adjustable bucket wheel 12. The bucket wheel 12 is designed so that it picks up in a single operation the entire gravel layer 5 which mostly has a thickness of 1 m to 1.5 m. Sand or earth layers 4, 6 which lie above and below it are also conveyed together with the gravel 5. Alternatively to a bucket wheel 12, a winning-head with a hose or telescopic tube (not shown) connected thereto can also be used as the winning unit 8. In this case, a compressed-air winning system, in which compressed air is forced into the hose or the telscopic tube in the region of the winning-head, presents itself as being suitable.

From the winning unit 8, the material won passes via a transport device 13, which can comprise, for example, one or more conveyor belts or conveyor tubes, into the treatment unit 9. Here, the material won is graded, washed in washing installations 14 and subjected to suitable separating processes to extract the mineral wealth contained. The waste 11 which occurs is then transferred to further transport devices 1 5 which can be controlled from the dredger. These deposit the waste 11 at predetermined points behind the dredger or to its sides. The Figure shows diagrammatically how a retaining dam 1 6 with overflow pipes 1 7 for the river water 3 is built up by means of the waste 11. All the functions of the floating dredger are controlled and monitored from a control post 1 8.

The floating dredger can be driven in a conventional way by propeller screws. However, it is advantageous to provide on the floating bodies 7 devices for supporting and progressively moving the floating dredger against the bottom of the river bed, in order to oppose effective counterforces against the applied pressure of the winning unit 8.

For example, piles (not shown) can be used to support and progressively move the floating dredger. In a preferred exemplary embodiment, there are provided vertically adjustable drive wheels 1 9 which can be pivoted to the side and which extend to the bottom of the excavated river bed and, at the same time, effect the progressive movement of the floating dredger. The drive wheels 19 can turn in all directions about a vertical axle 20. They enable the floating dredger to be steered into any position desired.

The floating dredger described makes it possible to carry out the process according to the invention even under extreme terrain and weather conditions. Associated with this is a hitherto unattained economy in the excavation of sands containing mineral wealth. When the process is carried out, a destroyed region is not left behind, as previously in the case of other excavation processes, but there are obtained causeways and a wide river with numerous dammed stages which permit considerable water storage and water regulation, above all in the rainy periods. In the dry season, the river valley can be irrigated from the large reservoir of water and, consequently, an intensive agricultural exploitation can be achieved.

The still waters of the dammed stages are, moreover, especially suitable for fish farming.

Thus, apart from the economical extraction of mineral wealth, an extraordinarily high economic utilisation of the entire land is achieved by means of the process according to the invention. After the excavation of the mineral wealth, a region which constitutes a self-contained and viable ecosystem is left behind.

Claims (12)

1. Process for the excavation of sands containing mineral wealth, in the region of a river bed, and for simultaneously improving the infrastructure in the landscape, by the use of a dredger, characterised in that a floating dredger is guided upstream and, in so doing, sand is excavated, this sand is graded and washed on the dredger and the waste is conveyed by a discharge unit for simultaneously damming the iver "1ater and building dammed stages, and is deposited to the side and/or downstream.

2. Process according to Claim 1, characterised in that there is used as floating dredger a bucketwheel dredger which is equipped with at least one pivotable conveyor belt or conveyor tube, by means of which the waste is conveyed and unloaded behind and/or to both sides of the floating dredger.

3. Process according to Claims 1 and 2, characterised in that retaining dams are built transversely through the river bed and/or along the river bank directly from the floating dredger, by means of at least a part of the waste.

4. Process according to Claims 1 to 3, characterised in that a part of the waste which is dumped directly from the floating dredger is used to build causeways along the river bank.

5. Floating dredger for carrying out the process according to one or more of Claims 1 to 4, characterised by one or more floating bodies of a small draught, on which are located a winning unit, a treatment unit and a discharge unit for waste.

6. Floating dredger according to Claim 5, characterised in that a vertically adjustable bucket wheel is provided as part of the winning unit.

7. Floating dredger according to Claim 5, characterised in that the winning unit consists of a winning-head and of a hose or telescopic tube which is connected thereto and into which compressed air is forced in the region of the winning-head.

8. Floating dredger according to Claim 5, characterised in that devices for supporting and for progressively moving the floating dredger against the bottom of the river bed are located on the floating bodies.

9. Floating dredger according to Claim 8, characterised in that piles are used to support and progressively move the floating dredger.

10. Floating dredger according to Claim 8, characterised in that vertically adjustable drive wheels which can be pivoted to the side about an axle are used to support the floating dredger.

11. A process for the excavation of sands substantially as hereinbefore described.

12. A floating dredger constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.