GB2200350A

GB2200350A - Process for producing granulated filter material for water purification

Info

Publication number: GB2200350A
Application number: GB8702002A
Authority: GB
Inventors: Evgeny Georgievich Petrov; Alexei Fedorovich Fadeev; Olga Vladimirovna Bazileva; Sergei Mikhailovich Levitin
Original assignee: LE I INZHENEROV ZHELEZNODOROZH
Current assignee: LE I INZHENEROV ZHELEZNODOROZH
Priority date: 1987-01-29
Filing date: 1987-01-29
Publication date: 1988-08-03
Anticipated expiration: 2007-01-29
Also published as: GB2200350B; FR2610533B1; GB8702002D0; FR2610533A1; DE3703169A1

Abstract

A process for producing a granulated filtering material for purification of naturally-occurring waters for the preparation of potable water comprises a fluidized-bed granulation of an aqueous suspension of china clay with an additive of powder- like dolomite in an amount of from 20 to 25% by mass of china clay, followed by calcination of the resulting granules at a temperature of from 900 to 950 DEG C inclusive.

Description

PROCESS FOR PRODUCING GRANULATED FILTER MATERIAL FOR WATER PURIFICATION The present invention relates to the art of puri fication of naturally-occurrin & waters for the preparation of potable water and, more specifically, to processes for producing a granulated filtering material for purification of naturally-occurrin# waters of medium and hign colour index. It should be also noted that,as a rule, naturally-occurring waters with medium and high colour index have a low turbidity.

It is known that colour index or chromaticity of naturally-occurring water is determined bs the presence of humus therein, while turbidity is defined by the presence of suspended matter.

Laown in the art is a process for producing a granulated filtering material for purification of na turally-occurriAg waters comprising granulation of finely divided natural clays in a fluidized bed, followed by calcination of the resulting granules at a temperature within the range of from 1,050 to l,2500C (cf.

V.N. Martensen, R.I. Agukaev, A.K. Strelkov, S.M. Shandalov, P.G. Eykowa "Crushed Claydite - New Filtering Aid for Water-Cleaning Filters", Kuibyshev, 1976, pp.33 -35).

This prior art process results in the filtering material featuring a very low adsorption capacity re lative to humus and suspended matter.

Also known in the art is a process for producing a granulated filtering material for purification of naturally-occurring waters comprising granulation of an aqueous suspension of natural clays in a fluidized bed with the addition of disintegrated magoetite, followed by calcination of the resulting granules at a temperature within the range of from 600 to 9000C (cf. USSR Inventor's Certificate No. 982723, Int.C13. B 01 D 23/10, published in the Official Bulletin "Discoveries, Inventions, Industrial Designs, Trademarks" No. 47, 23.

12.82.).

This process, however, enables only an insignificant improvement of the adsorption activity of the filtering material relative to humus and suspended matter being present in naturally-occurring water.

Also known in the art is a process for producing a granulating riltering material for purification of naturally-occurring waters comprising a fluidized-bed granulation of an aqueous suspension of china clay with the addition of a powder-like magnesium carbonate in an amount of from 15 to 30 % by mass of china clay, followed by roasting of the obtained granules at a temperature of 850-9000C (of. USSR Inventor's Certificate No. 1152650, Int.Cl. B 01 J 20/02 published in the Official Bulletin "Discoveries, Inventions, Industrial Designs, Trademarks" No. lb, 30.04.8 > -).

This process makes it possible to considerably improve the adsorption capacity of the granulated tering material relative to humus and suspended matter.

This, in turn, enables purification of naturally-occurring waters to obtain potable water of a sufficiently high quality. However, the auration of a filtering cycle Sr this filtering material is not long, thus ne cessitating frequent shutdowns of filtering racilities for regeneration of the filtering material which renders the process of purirication of naturally-occurring waters more expensive.

There is another known process for producing a granulatea filtering material for purification of naturallg-occurring waters comprising a rluidized-bed granulation of an aqueous suspension of natural clays with the addition of a powder-like naturally-occurring raw material based on carbonates of calcium and magnesium, namely limestone containing from 7 to 24% by mass of magnesium carbonate, in an amount of 20 to 40% by mass of the clay, followed by calcination of the resulting granules at a temperature within the range of from 700 to 9000C (cur. USSR Inventors Certificate No. 1033179, Int.Cl.3 B 01 J 20/03 published in the Official bulletin "Discoveries, Inventions, Industrial Designs, Trademarks" No. 29, 07.08.83).

This process enables only insignificant improvement of the adsorption activity of the filtering material relative to humus and suspended matter.

In all of the abovewdiscussed prior art pro cesses, except the process according to the USSR Invent orts Certificate No. 1152650, a granulated filtering material is obtained wnich functions only upon the addition of a coagulation agent into the water being treated, e.g. aluminium sulphate. The presence of Al-ion in the purified water imparts toxicological properties to the latter. Burthermore, at a high colour index of the purified water it is impossible to lower this index to a va- lue meeting the requirements imposed on quality of potable water.

It is an object of the present invention to provide such a process for producing a granulated filtering material for purification of naturally-occurring waters which would make it possible to produce a filtering material with a high adsorption activity relative to humus and suspended matter, would have a lasting filtering cycle and ensure a highly effective purification of naturally-occurring water without the addition of a coagulation agent thereto.

This object is accomplished by a process for producing a granulated filtering material for purification of naturally occurring waters comprising a fluidized-bed granulation of an aqueous suspension of china clay with an additive of powder-like dolomite in an amount of from 20 to 25S by mass of china clay, follow- ed by calcination of the resulting granules at a temperature of from 900 to 9500C.

Dolomite comprises a mineral consisting of 12 -26% by grass of calcium carbonate and ou-74 by mass of magnesium carbonate.

Powder e dolomite employed in the process according to the present invention is completely decomposed within the entire volume of granules upon calcination at the above-mentioned temperature with the iormation of oxides of magnesium and calcium with their microcrystals serving as active centers promoting an intensive adsorption of humus and suspended matter on the surface of a granulated filtering material.Consequently, the process according to the present invention makes it possible to obtain a granulated filtering material with a high adsorption activity relative to humus and suspended matter. this filtering material features a lasting filtering cycle which makes it possible to avoid frequent shut-downs of filtering taci- lities for regeneration of the riltering material and to make the process of purification of natural waters less expensive. J?urthermore, such filtering material operates without the addition of a coagulation agent to the water being treated which simplifies the process of water purification and lowers costs of purification of naturally-occurring water. All this enables an efficient purification of naturally-occurring waters and production of a high-quality potable water.

It should be noted that dolomite employed as an additive in the process according to the present in vention is a Widely available naturally-occurring raw material.

As it has been already mentioned hereinbefore, calcination of granules is carried out at a temperature within the range of from 900 to 95000. It is inadvisable to conduct calcination at a temperature below 90000, since at lower calcination temperatures the resulting granules have an insufficient mechanical strength.Fur- thermore, at low temperatures of calcination dolomite is not fully decomposed with the formation or oxides of magnesium and calcium which results in a lowered activity of adsorption of the filtration material. It is neither advisable to carry out calcination of granul- es at a temperature above 95000, since non-productive consumption of energy''owl calcination is increased.

In the process according to the present invention powder-like dolomite is used in an amount of from 20 to 25% by mass of china clay. It is inadvisable to use dolomite in an amount below 20% by mass of china clay, since adsorption activity of the resulting filtering material relative to humus and suspended matter being present in naturally-occurring water is considerably lowered. It is inexpedient to use dolomite in an amount of more than 25S by mass of china clay, since adsorption activity of the filtering material is not substantially increased, while mechanical strength of granules is lowered.

The process for producing a granulated filtering material according to the present invention is performed in the following manner. An aqueous suspension of china clay is prepared with an additive of powderlike dolomite which is employed in an amount of 20 to 25% by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) to the liquid phase in the suspension is varied within the range of from 1:1.5 to 1:2 respectively. The resulting suspension is granulated in a fluidized-bed apparatus. Tile thus-produced granules are subjected to calcination at a temperature ranging rrom 900 to 95000 and then cooled. The calcination of granules can be effected either in the same apparatus, or outside it, for example in a calcination furnace.

As a result, a filtering material is obtained in the form of a mixture of granules with a diameter of from 0.5 to 2 mm.

The granulated filtering material produced by the process according to the present invention can be effectively employed in filtration facilities operating on the principle of both ascending and descending filtration. In doing so, a high quality of purification of waste waters is ensured without the addition of a coagulation agent to the water being purified.

Por a better understanding of the present invention, some specific examples illustrating its particular embodiujents are given hereinbelow.

Example 1 An aqueous suspension of china clay is prepared with the addition of powder-like dolomite consisting of 16% by mass of CaCO3 and 84% by ass of ggC05 employea in the amount of 20* by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) to the liquid phase in the suspension is 1:1.5 respectively. The resulting suspension is granulated in a rluidi- zed-bed apparatus. The thus-produced granules are discharged from the apparatus and fed into a calcination furnace, wherein they are subjected to calcination at the temperature of 9000C. Thereafter, the granules are cooled.

As a result, a filtering material is obtained as a mixture of granules with a diameter of rrom 0.5 to 2.0 mm.

Example 2 An aqueous suspension of china clay is prepared with the addition of powder-like dolomite consisting of 26% by mass of CaCO3 and 74% by mass of #CO3 taken in the amount of 25% by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) to the liquid phase in the suspension is equal to 1:2 respectively. The resulting suspension is granulated in a fluidized-bed apparatus. The thus-produced granules are subjected to calcination at the temperature of 950 C. Then the granules are discharged from the apparatus and cooled.

As a result, a filtering material is obtained in the form of a mixture of granules with a diameter of from 0.5 to 2.0 mm.

sample 3 A granulated filtering material is produced in a manner similar to that described in Example 1 here in before. Dolomite consisting of 26% by mass of CaCO3 and 74% by mass of MgCO3 is employed in the amount of 25% by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) to the liquid phase in the suspension is equal to 1:2 respectively. The temperature of calcination of granules is 95000.

sample 4 A granulated filtering material is obtained in a manner similar to that described in Example 1. Dolomite zilch consists of 22% by mass of CaCOf and 38 > by mass of MgCO3 is used in the amount of 22% by mass of china clay. The mass ratio of the solid phase (china clay witn dolomite) to the liquid phase of the suspension is equal to 1:1.75 respectively. The temperature or calcination of granules is 92000.

Example 5 A granulated filtering material is obtained in a manner similar to that described in Example 2 here inbef ore. Dolomite consisting of 16% by mass of CaCO3 and 84% by mass of MgCO) is used in the amount of 20% by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) to the liquid phase in the suspension is equal to 1:1.5 respectively.The temperature of calcination of granules is 900 C.

Example 6 A granulated filtering material is obtained as in Example 2. In doing so, dolomite consisting of 12% by mass of CaCO3 and 78% by mass of 44COD is used in the amount of 22% by mass of china clay. The mass ratio of the solid phase (china clay with dolomite) in the suspension is equal to lr1.75 respectively. The temperature of calcination of the granules is equal to 9200 C.

The granulated filtering material produced in the roregoing Examples 1 through 6, as well as granulated filtering materials produced by the processes according to the USSR Inventor's Certificates Nos 1152650 and 1033179 were tested for an adsorption activity relative te humus Substances causing hromaticity of naturally-occurring water. In these tests use was made of filtering materials with a traction of granules with a diameter of 1.0-1.2 mm. Tests were conducted in the following manner. A weighed sample (10 g) of each filtering material was placed into a flask with 100 ml of a peat extract with the colour index of 500 degrees.

The flask with its contents were slightly shaken every 2 hours.

The adsorption activity of each filtering material was determined by diminition of the intensity of colour of the peat extract (due to adsorption of humus matter on the surface of the riltering material granules) after residence for 24 hours. The obtained test results are given in Table 1 hereinbelow. Also given in Table 1 are the data illustrating the discoloration efrect which is determined as a ratio of the value of decrease of the peat extract colour index to the value of its initial colour index expressed in per cent.

As it is seen from Table 1, the granulated filtering material produced by the process according to the present invention (examples 1 through 6) is superior, as regards the discoloration effect, to the material produced according to the USSR Inventor's Certiricate No. 115265w by 1.4-1.6 times and to the filtering material produced according to the USSR Inventor's Certificate No. 1053179 - by 2.7-3 times.

The granulated filtering material produced by the process according vo the present invention in Examples 1 to 6 and the granulated filtering materials produced according to the USSR Inventor's Certificate Nos 1152650 and 1033179 were tested in purification of river water of a high chromaticity having the rollowing characteristics: colour index - 210 degrees, turbidity - 8 mg/l, pR = 6.7. The tests were conducted on a test stand consisting of three filtering columns having the diameter of 50 mm and height of 2,000 mm.

Into the first column the filtering material produced by the process according to the present invention was charged, into the second column - the filtering material produced according to the USSR Inventor's Certi ticate No. 1152650 and into the third column - the filtering material produced by the process according Table 1 Granulated p amount absorption activity of p and amount the filtering material filtering of the additive relative to humus matter material employed,% by mass mass of china colour Decrease Discolo- to clay a peat of of index tract a- of peat effect, ter resi- extract, science for degrees 24 hours, degr.

Examples 1 and 5 Dolomite - 20 280 220 44 Examples 2 and 3 Dolomite - 25 260 240 48 Examples Dolomite - 22 275 225 45 4 and 6 USSR Inventor's certificate Magnesium car No. 1152650 bonate - 30 350 150 30 USSR Inventor's certificate Limestone con No. 1033179 taining 14% by mass of MgCO? - 30 420 80 16 to the USSR Inventor's Certificate No. 1033179. The filtering materials comprised the fraction of granules with a diameter of 1.0-1.2 mm. The height of the filtering material bed in each column was 1,000 mm. The filtration of river water was erfected in the downward direction. The filtration rate was kept constant and equal to 5 m/h. No coagulation agent was added to the purified river water prior to its filtration.

The criterion of efficiency of operation of the filtering materials was. the amount of purified river water during one filtration cycle. The filtration cycle means a period of time during which a purified water comes out of a filtration column which meets the requirements imposed on potable water as regards its chromaticity and turbidity, namely: colour index - not higher than 20 degrees, turbidity - not more than 1.5 mg/L.

Filtration of the river water was ertected for 10 hours, chromaticity and turbidity of the filtrate were determined every hour.

The results of process tests of the granulated filtering materials produced by the process according to the present invention and according to the USSR Inventor's Certificates Nos. 1152650 and 1033179 are -shown in Table 2 hereinbelow.

Table 2 Time since Granulated filtering material beginning according to the process o this invention of the fil- with dolomite in the wita dolomite in the tration, h amount of 20% ty mass amount of 22% by mass

ples I and 5 am- 4 and pies colour in- turbidity colour in- turbidity jew of the of the fil- dex of the of the iterate, trate,mg/l filtrate, r filtrate, degrees degreea mg/l I 2 degrees I 12 0.8 9 0.8 2 12 0.8 10 0.8 3 14 0.8 11 0.9 4 15 0.9 11 0.8 5 15 0.9 12 0.9 6 17 1.1 14 1.0 7 19 1.2 17 1.0 8 20 1.3 20 1.1 Table 2 (continued) 1 2 3 4 5 9 25 1.4 23 1.2 10 30 1.6 27 1.4 Table 2 (continued) Granulatea filtering material since beginn- of this invention of the prior art ing of with dolomite in USSR Inventor's Certificates the the amount of 25% No.1132650 No.1033179 ftiilotJ,a mags of 2.3) with MgCO3 with limestone in the amo- containing 14% unt of 30% by mass of by mass or MgC03 in the china clay amount of 30% by mass of china clay colour in- tu@@idi- colour turbi- color turbi dex or the ty of the index dity index dity filtrate, filtrate of the the of the of degrees mg/l degrees filt- filt- the rate, rate, fil- mg/l degreestrate, mg/l 1 6 7 8 9 10 11 1 8 0.7 12 0.8 55 2.4 2 9 0.7 14 0.9 60 2.6 3 10 0.7 16 1.0 70 2.9 4 11 0.8 17 1.1 75 3.0 5 12 0.8 20 1.1 85 3.3 6 13 0.9 23 1.3 90 3.5 7 15 1.0 28 1.4 100 3.7 8 18 1.1 35 1.6 115 3.9 9 20 1.2 45 1.8 120 4.0 10 23 1.2 35 2.0 135 4.4 It follows from the above Table 2 that duration of one filtration cycle for the granulated filtering material produced by the process according to the present invention has the following parameters, hours:: with the addition of dolomite in the amount of 20% by mass of china clay (Esamples 1 and 5) 8 with the addition of dolomite in the amount of 22% by mass of china clay (Examples 4 and 6) 8 with the addition of dolomite in the amount of 25% by mass of china clay (Examples 2 and 3) 9.

The duration of one filtration cycle for the granulated filtering material produced by the process ac croding to the USSR Inventor's Certificate No. 1152650 is 5 hours. Upon riltration of river water through the granulated filtering material produced according to the USSR Inventor's Certificate No. 1033179 the filtrate does not meet the requirements imposed on quality of potable water during the entire time of the filtration.

It also follows from the above Table 2 that the duration of the filtration cycle of the filtering material produced by the process according to the present invention is by 1.6-1.8 times higher than the same parameter for the filtering material produced by the process according to the USSR Inventor's Certificate No. 1152650.

Furthermore, it is seen from Table 2 hereinabove that the filtration material produced by the process according to the present invention is more effective, as compared to the riltering materials produced according to the USSR Inventors Certificates Nos. 1152650 and 1033179, in purirication of naturally-occurring water rrom suspended matter Therefore, the process according to the present invention makes it possible to produce a granulated filtering material with a high adsorption activity relative to humus and suspended matter, it also has a lasting filtration cycle. This filtering material effectively purifies naturally-occurring waters without the addition of a coagulation agent thereto, thus excluding preparation of potable water having toxicological characteristics.

All the foregoing makes it possible to substantial ly improve efficiency of operation of filtration facilities for purification of naturallg-occurring waters and to obtain a high-quality potable water.

Claims

1. A process tor producing a granulated filtering material ror purification of naturally-occurring waters comprising a fluidized-bed granulation of an aqueous suspension of china clay with an additive of powder-like dolomite in an amount of from 20 to 25X by mass of china clay, followed by calcination of the resulting granules at a temperature within the range of from 900 to 9500 C.

2. A process for producing a granulated filtering material tor purification of naturally-occurring waters, substantially as described in the Specirication and samples 1 to b given hereinbefore.

3. A granulated filtering material tor purification of naturally-occurring waters, whenever produced by the process according to the foregoing Claims 1 and 2