FI95561C - Procedure for reducing the aluminum content in drinking water - Google Patents

Description

95561

Method for reducing the aluminum content of drinking water.

The invention relates to a method for removing low aluminum concentrations in natural waters and waters treated with aluminum-based chemicals. In more detail, the raw water is passed through a serpentinite stone statue.

Surface water is rarely of such quality that it can be used as it is without treatment. Chemical precipitation 10 is one purification method in which, in the flocculation phase, e.g. aluminum sulfate and polyaluminum salts. Even after removal of the precipitated sludge and sand filtration and possible active filtration, these may still leave residual aluminum in the water, which is good to remove. In Finland, domestic water quality standards have been drawn up and in 1991 the target value for aluminum was set at 0.2 mg / l.

Normally, filtration is used in the production of high quality water as a complement to clarification and flotation. Among other things, the ke-20 chemical floc is separated by mixing and possibly filtration. One or more layers of sand are used in the filtration as a filter medium, in some cases activated carbon.

Finnish Patent Publication No. 65217 discloses an aqueous aluminum composition which, when flocculating water, gives a lower residual aluminum content than when using conventional sulphates. In this case, the flocculates obtained and thus also the impurities are removed from the water 30 by a settling and / or sand filtration method.

*. Finnish patent application No. 255/74 discloses a combination filter for purifying water. In the publication, a coarse non-fibrous mat is placed in connection with the microfilter and the microfilter-35 is made of inorganic or organic fibers: a tissue-reinforced membrane filter and passes through 95561 2 a tissue-reinforced membrane filter and passes only particles up to 1 μπκ

Finnish patent application No. 890426 discloses a basic aluminum chlorosulphate which, when used, leaves very little residual aluminum in the treated water. In the production of drinking water, it has been found that the higher the alkalinity, the lower the values of residual aluminum.

10 Finnish patent publications No 83163 and No 84140 present the possibility of purifying natural waters into drinking water. The filter media are obtained by granulation.

Finnish patent application No. 882218 describes a method for removing metal ions, such as Ag, Pb, Cr (III), Zn and Ni, from wastewater by means of alkaline earth silicate.

Finnish patent application No. 902984 discloses the treatment of waters containing dissolved aluminum.

The method comprises dissolving a silicon source and a base source in water, as a result of which the aluminum is converted into a non-toxic form.

U.S. Patent No. 4,256,577 discloses a process for removing metal ions such as manganese, copper, cadmium, lead, iron, cobalt, nickel, zinc and chromium by contacting water with magnesium silicate.

Residual aluminum must not exceed 0.2 mg / l in drinking water, which is considered a limit in eg the EC directive. Residual aluminum: is not only harmful to health but also an undesirable substance due to its corrosion and precipitation properties.

It comes not only from the raw water itself but also and mainly from 35 coagulants, i.e. e.g. aluminum sulphate and aluminum chlorides. Most of the aluminum is removed by precipitation, whereby • the precipitate is separated by settling and / or flotation and the aluminum in the form of 3 95561 is removed by sand filtration. The amount of soluble aluminum also depends on e.g. variation in the precipitation pH, possible dosing disturbances in the chemical, raw water quality and water temperature.

5

It has now surprisingly been observed that by passing raw water through a certain type of serpentinite stone column, the concentration of aluminum in soluble form is also clearly reduced.

Characteristic features of the invention appear from the appended claims 1-3.

More specifically, the method of the invention is directed to passing raw water through hydroxide silicate minerals to which aluminum binds aluminum. Essentially present in the hydroxide silicate rock is basic magnesium silicates such as serpentine. The serpentinite rock material according to the invention has a MgO content of between 25 and 45% by weight and a SiO2 content of between 25 and 45% by weight.

The weight ratio of MgO: SiO 2 is between 0.8 and 1.2.

If necessary, both the temperature and the pH value are adjusted already during the Flok season.

An essential part of the serpentinite rock is the above-mentioned basic magnesium silicate. It is pure, for example, a monoclinic, fine-crystalline magnesium silicate of the formula [(OH) 4 Mg 3 (Si 2 O 5)], in which case the lattice may contain small amounts of iron. It belongs to the mesh silicates being a finely divided mass. The serpentinite filter material according to the invention can be further described as follows - due to its structure it is not "slippery" - easy to slurry in water. a lot of free bonding possibilities - large specific surface area, ranges are 35 25 - 70 m2 / g (depending on fineness) - cationicity suitable. For example, when the fineness is 95% to 20 βχα, it is 0.12 ml kv / g.

95561 4 - pH of aqueous slurry suitable (8 - 9.5)

The following example illustrates the effectiveness of the process of the invention for removing residual aluminum when raw water is passed through a serpentinite stone column.

Example

The example used humus-containing surface water flocculated with aluminum sulfate and sodium aluminate, from which the floc was separated by flotation. The aluminum content of the water after flotation separation was periodically increased by adding pure Al solution to the water. Water was passed through a 20 cm high serpentinite statue with a surface load of 0.5 m / h, with a residence time in the statue of about 20 min, Fig. 1. The total aluminum content of the water fed to the statue averaged 0.5 mg / l, occasionally over 1 mg / l. Of this, soluble aluminum accounted for up to 80%.

The following figures show the method according to the invention.

Figure 1.

The total aluminum content of the water filtered through the statue was <0.02 mg / l when water was passed through serpentinite at about 4000 m3 / m2, and the capacity remained, Figure 2.

Figure 2.

Serpentinite also has a beneficial effect of raising the pH by 0.5-1 units.

30

Claims (3)

95561 1. A process for the preparation of drinking water for removing at least dissolved aluminum from raw water after possible chemical precipitation, characterized in that the raw water is passed through a serpentinite stone column with a MgO content of 25 to 45% by weight of the serpentinite rock. Process according to Claim 1, characterized in that the serpentinite stone has an MgO content of between 25 and 45% by weight, a SiO 2 content of between 25 and 45% by weight, a weight ratio of Mg O: SiO 2 of between 0.8 and 1.2 and the aqueous slurry is alkaline. Process according to Claim 1, characterized in that the specific surface area of the serpentinite stone is between 25 and 70 m 2 / g. 6 95561 1. For example, the elixination of the feedstock is determined by the addition of 5 aluminums in the form of a solid-state solution after the eventual chemical reaction of the inverted LEDs in a column of serpentines, with a low MgO content of 25 to 45%. 10 2. A preferred embodiment of claim 1 comprises a solution of 25 to 45% by weight of MgO, with 25 to 45% by weight of SiO2, a minimum of 25% to 45% by weight of MgO: 0.8 to 1.2% by weight of SiO2. är basisk. 15 3. A preferred embodiment of claim 1 is a serum with a specific specification of 25 to 70 m2 / g. il lit »llill IM