SU1669857A1 - Method for obtaining phosphoric acid - Google Patents

Abstract

The invention relates to the technology of inorganic substances, in particular to methods for producing phosphoric acid. To reduce the incrustation of salts on the steel surfaces of vacuum filters, their anodic polarization to potentials of 0.2–1.0 V relative to the graphite cathode has been proposed. The use of the method allows to reduce the consumption of reagents that prevent the incrustation of salts, and to increase the productivity of the process by reducing the overhead of the equipment operating time. 1 tab.

Description

This invention relates to a technology of inorganic substances, in particular to an extraction method for producing phosphoric acid.

The aim of the invention is to reduce the consumption of materials and increase the productivity of the process.

Example Into a cascade of 100 m reactors, 8 t / h of apatite concentrate are fed. 7.8 t / h of sulfuric acid, 24 t / h of circulating phosphoric acid and recirculating pulp, 0.25 t / h of soda ash (with the aim of defluorinating the acid). The decomposition of apatite is carried out at 100-107 ° C, F: T 3.5-4 0 From the last reactor, the slurry is fed to three belt vacuum filters. The surface of one of the filters made of steel EI-943 and in contact with 111 and IV filtrates was subjected to anodic polarization to a potential of +1.0 V relative to the graphite cathode installed on the calcium sulphate sediment over the third and fourth filtration zones. The fourth filtration zone clogged up on the 16th day of the filter operation, at the same time, the anodic polarization filters were blocked by sediment after 2-3 days of operation.

EXAMPLE 2 Under the same conditions as in example 1, the surface of the filter of the third and fourth zones was subjected to anodic polarization to a potential of +0.2 V. After 6 days of operation of the filter, a precipitate was found on the third filtration zone, there is no fourth draft. Filters without anodic polarization of the surface were clogged with sediment after 2-3 days of operation.

As follows from the above data, the use of anodic polarization of the metal surfaces of the vacuum filter in contact with the reaction mixture up to +1.0 V relative to the graphite cathode makes it possible to increase the filter operation time by more than 6 times (example 1). Under similar conditions, the polarization of the same filter surfaces only up to 2 V relative to the graphite cathode leads to a decrease in the positive effect, scoring (/

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As a result of salt inlay, the filter already occurs after 6 days of operation, i.e. the operation time is only doubled.

The table shows the effect of the potential of anodic polarization on the corrosion of EI-943 steel under conditions of the preparation of hemihydrate phosphoric acid.

The increase in the value of anodic polarization of the surface of high-alloy steel equipment over +1.0 V relative to the graphite cathode leads to its intense corrosion.

A decrease in the anodic polarization below +0.2 V leads to salt incrustation.

Thus, a positive effect is achieved only in the claimed range of polarization values of the steel surfaces of the filters relative to the graphite cathode.

By comparing the proposed technical solution with the known one, it should be noted that a positive effect is achieved due to

anodic polarization of the metal surfaces of the process equipment in contact with the reaction mixture, on which salt incrustation is possible.

The proposed method of obtaining phosphoric acid extraction makes it possible to completely eliminate the introduction of additives into the reaction mixture, reduce the time of preventive stops and washes of the process equipment and thereby increase the productivity of the process as a whole.

Claims (1)

Claims A method for producing phosphoric acid, which includes decomposition of phosphoric raw materials followed by separation and washing of calcium sulfate on high alloy steel filters, characterized in that, in order to increase productivity, the surfaces of the filters are anodically polarized relative to the graphite cathode to. 0.2-1.0 V.