RO117265B1 - Process for preparing a pigment based on iron oxide - Google Patents

Abstract

The invention presents a process for preparing a pigment based on iron oxide having a content of 30...70 % of Fe2O3, 3...20% SiO2, 2...18% of Al2O3 and 3...20% of CaO by purifying the red slurry resulting from the bauxite processing by fractional settling, screening and washing thereafter in order to reduce the content of water-soluble substances under 1%. After filtration, an aqueous part having a humidity of 40...50% is produced, and subjected to a homogenizing phase, when calcium silicate is added thereto in a ratio of 4...6%, and 2% of zinc oxide. The resulting mixture is dried and ground.

Description

RO 117265 B

The invention refers to a process for obtaining a pigment, based on iron oxide from the red sludge from the processing of iron-rich bauxite, used to obtain anti-corrosive primers, coating paints and in construction to color concrete.

A process for obtaining a pigment based on ferric oxide from red mud is known, which consists of filtering, calcining and grinding it.

A process is also known for obtaining a pigment based on ferric oxide from red mud, preceded by a preliminary sorting by hydrocycling and an iron oxide enrichment of the pigment by additions of ferrous sulfate before calcination.

The disadvantages of this procedure are the following:

- sorting by hydrocycling is a cumbersome process, the machine easily malfunctions;

- the desired results are not always achieved, for the same purpose a process is also known for the preparation of some iron oxide pigments for paints, from the red sludge from the processing of bauxite by treatment with ferrous sulfate heptahydrate and calcination, at 400...800 °C.

Also known are processes for obtaining anticorrosive pigments based on calcium oxide, aluminum and iron by coprecipitation.

, These procedures present the following disadvantages:

- it does not provide effective anti-corrosion protection, because mechanical impurities are not removed;

- the content of calcium silico-aluminates whose presence improves the anticorrosive power of the pigment is not monitored.

The process, according to the invention, removes the disadvantages mentioned in that the red sludge is acidified with sulfuric acid to correct the pH to a value of 8...9, the acidified red sludge is washed by filtration, in order to reduce the water-soluble substance , at a value below 1% when obtaining an aqueous part whose humidity is 40,...50% which is subjected to a homogenization phase where 4...6% calcium silicate and 2% oxide of calcium are added zinc, and finally, after homogenization, the obtained mixture is dried and ground, to a maximum fineness of 1...5%, on sieve no. 0063.

By applying the invention, the following advantages are obtained:

- reduced washing time;

- reduced consumption of washing water;

- the obtained pigment has a soft texture due to the omission of the calcination phase;

- the obtained pigment has a slightly alkaline pH;

- the anticorrosive character is accentuated, long-lasting, due to the presence of zinc oxide and the Ca/Si ion exchange;

- the product obtained has a non-toxic character, thus allowing to obtain anti-corrosive primers, with effects comparable to those of primers obtained based on lead minium and zinc chromate, which are toxic.

Next, 3 examples of the invention are given.

Example 1. From red mud previously purified by sieving and fractional sedimentation, having a pH of 11...12, a solids content of 180...200 g/l and a granulation of 95% below 60 m 5 I are introduced into a cylindrical glass vessel. The pigment is washed with water by repeated decanting, 3 times, then under stirring

Claims (1)

RO 117265 B continues, the pH is corrected by adding 10% sulfuric acid, up to a pH value of 8...10. It is then washed by repeated decanting to reduce the content of water-soluble substances below 1%, then it is filtered, dried at a temperature of 105...140^ to a maximum moisture of 1...5% and ground to obtain the desired degree of fineness. In this way, an anti-corrosive pigment is obtained with the efficiency comparable to that of lead mini. Example 2. The red mud from the processing of bauxite, according to the Bayer method, with a solids content of 40...200 g/l, a pH of 11...12.5, is 55 continuously captured in a 500 cm ³ vessel, where fractional sedimentation takes place. The coarse part is continuously removed at the bottom of the vessel, and the fine part is captured by means of a side spigot and transferred to the washing or directed to the vibrating screens. The sieved material is washed at an S:L weight ratio of 1:20 until the water-soluble content is reduced to below 2% expressed as 60 dry matter. Reducing the pH to 8...10 is achieved with concentrated sulfuric acid, by adding it after the first wash water, in order to reduce the amount of sulfuric acid used. After washing, the aqueous suspension is filtered to obtain an aqueous paste of 40...60% pigment suitable for drying. 65 Drying takes place at a temperature of 1O5...14O°C until a maximum humidity of 5% is obtained. The dry pigment is captured in a homogenization hopper where, as appropriate, 4...6% calcium silicate, 2% zinc oxide and surfactants are added. After homogenization, the pigment is packed in paper bags of 20...40 kg. 70 Example 3. The red mud from the processing of bauxite by the Bayer method, with a solid substance content of 40...200 g/l, pH, of 11...12.5 is directed to the vibrating screens. The sieved material is acidified to a pH of 8..10. The sieved and acidified material is filtered to obtain an aqueous portion of 75 40...60% pigment suitable for drying. the removal of water-soluble substances is done by washing with water directly in the filter press. Drying takes place at a temperature of 400...500°C followed by grinding to obtain the desired fineness with a maximum of 5% residue on the 0.063 us sieve. The dry material is collected in a homogenizer from which it is then packed into paper bags or containers. Claim Process for obtaining a pigment based on iron oxide with a content of 85 30...70% Fe ₂ 0 ₃ , 3...20% SiOg, 2...18% AI ₂ O ₃ and 3... 20% CaO, by purifying the red mud, resulting from the processing of bauxite with a solid content of 10...200 g/l, by fractional settling followed by sieving and washing, characterized by acidifying the red mud with acid sulfuric acid to correct the pH to a value of 8...9, the acidified red sludge is washed by filtration, in order to reduce 90% of the water-soluble substance to a value below 1% when an aqueous part is obtained which RO 117265 B humidity is 40...50%, which is subjected to a homogenization phase where 4...B% calcium silicate and 2% zinc oxide are added, and finally, after homogenization, the obtained mixture is dried and grind to a fineness of maximum 1...5% on sieve no. 95 0063. The president of the examination committee: Eng. Florea Stela Examiner: engineer Andrei Ana Editing and computerized techno-editing - OSIM Printed at: State Office for Inventions and Trademarks