Solid material comminution or disintegration – Processes – Application of solids to material
Reexamination Certificate
1999-09-22
2001-04-10
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
Application of solids to material
Reexamination Certificate
active
06213416
ABSTRACT:
BACKGROUND TO THE INVENTION
The present invention relates to treatment of phosphate-containing rock in processes which involve a grinding stage and in particular relates to improvement of the materials handling characteristics of the phosphate-containing rock.
It is well known that phosphate-containing rock (often referred to simply as “phosphate rock”) can be used to produce various materials containing phosphorus. The phosphate rock which is to be treated to produce a final product is generally obtained by first mining the rock, then pre-treating it by means of a series of flotation and physical separation stages. For many processes the rock has traditionally been additionally pre-treated in a fluidised bed drier.
These pre-treatment stages may take place before the phosphate rock is transported to the processing plant, in which the treatment process to produce the final product is to take place. Alternatively one or more of the pre-treatment stages may take place at the processing plant after transportation. The pre-treated rock is then transferred, within the processing plant, to the treatment stages. In various known processes, a grinding stage is included. One such process is the production of granular triple super phosphate (GTSP), in which phosphate rock is ground and added to hot phosphoric acid.
Use of the fluid bed drier pre-treatment stage adds expense to a process and it has of late been felt to be economically desirable to avoid this stage and instead to use phosphate rock which has not been subjected to a fluid bed drying stage. Such rock is often described as “raw” (or “wet”) phosphate rock.
However, it has also been found that use of raw phosphate rock in processes which comprise a grinding stage can lead to serious problems. In particular, the materials handling properties of the raw phosphate rock can be highly inconsistent. For the operation of grinding apparatus of the type commonly in place in many processing plants it is most important that the flow of the phosphate rock to the grinding apparatus is steady and consistent. If flow is inconsistent then the apparatus, which is designed to operate continuously, is forced to operate for certain periods of time in the absence of rock. This is a serious problem and leads to excessive wear on the grinding surfaces. This greatly increases the maintenance cost of the grinding apparatus. The poor properties of the raw phosphate rock which give rise to such problems also lead to significant production losses.
It is an object of the invention to improve the efficiency of processes in which raw phosphate rock is subjected to a grinding stage. In particular it is an object of the invention to improve the properties of the raw phosphate rock.
SUMMARY OF THE INVENTION
We believe that these problems can be attributed at least partially to the presence of water and contaminants in the raw phosphate rock supplied to the processing plant. We have also found that the materials handling properties of the raw phosphate rock can be improved dramatically by the addition of water-absorbent, water-insoluble, water-swellable polymer to the rock.
According to the invention we provide a process of treating phosphate-containing rock by grinding, the process comprising
(a) providing phosphate-containing rock which contains from 3 to 25 wt % water,
(b) transferring the phosphate-containing rock to a grinding apparatus during a transfer stage, and
(c) grinding the phosphate-containing rock in grinding apparatus, wherein the process comprises mixing particles of water-swellable, water-insoluble polymeric material, with the phosphate-containing rock before or during the transfer stage whereby the flowability of the rock into the grinding apparatus is improved.
The advantages of the invention include the fact that plant apparatus designed for treatment of phosphate rock which has been pretreated by a drying stage such as fluid-bed drying can be used for treating raw phosphate rock without modification of the apparatus.
We find surprisingly that the addition of the superabsorbent polymer has a significant effect on the materials handling properties of the raw phosphate rock. We find this particularly surprising in view of the fact that we have also found that traditional viscosity modifiers and dispersants such as the very low molecular weight sodium polyacrylates, which are known to be useful for the modification of the viscosity and flow properties of mineral slurries, are ineffective.
It is well known that water-absorbent particulate polymeric material absorbs water from its surrounding environment and the use of water-swellable, water-insoluble polymeric materials is known in many fields. For instance, it is known in the production of diapers.
It is also known to include water-absorbent, water-swellable polymers in a growth medium such as sand in order to increase the water absorption capacity of the growth medium, as described in for instance EP 001,253.
Water-absorbent polymers are also known for the treatment of mineral materials in the coal industry. For instance, in our publication EP-A-277,017 we describe the use of absorbent polymeric particles for mixing with sticky coal fines filter cake in order to make a non-sticky, friable fuel. In this process the polymeric particles are blended primarily with coal fines, which tend to have size mainly below 0.5 mm and substantially below 100 &mgr;m. The fines and polymeric particles can also be blended at the same time with coal smalls, which generally have size from 2 to 10 mm. This invention is said to be particularly useful for the production of filter cake which can subsequently be stored or transported by vehicle.
In our publication EP-A-195,550, we describe a more general process in which a slurry or cake is converted to a crumbly state by admixture with water-swellable cross-linked synthetic polymer particles.
EP-A-195,550 is particularly concerned with the problem of a wet particulate mass which must be transported in railway trucks under potentially cold conditions and thus tends to freeze solid in the trucks. The use of polymer particles is said to ensure that the mass remains crumbly within the truck and can be removed easily. The wet particulate mass is preferably mineral ore such as iron ore or coal but can also be sand, china clay, crushed mineral, red mud deposits, or phosphate slime.
EP-A-277,018 describes use of specific water-absorbent polymer particles for conversion of a sticky mass into a crumbly mass, which can be a mass as in EP-A-195,550 above.
However, none of these various publications and known uses of water-absorbent polymers address the problem with which the present invention is concerned, which is the specific problem of the inconsistent materials handling characteristics of raw phosphate rock when it is required to be transferred to a grinding stage.
REFERENCES:
patent: 3852403 (1974-12-01), Booth
patent: 3868243 (1975-02-01), MacDonald
patent: 4309222 (1982-01-01), Hoyt
patent: 5183211 (1993-02-01), Malito et al.
patent: 0 101 253 (1983-03-01), None
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patent: 0 095 091 (1999-03-01), None
Ciba Specialty Chemicals Water Treatments Ltd.
Crichton David R.
Rosenbaum Mark
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