DE3226306A1 - Process for the separation of heavy metal ions from crude phosphate - Google Patents

Abstract

A process for the separation of heavy metal ions such as cadmium or mercury from crude phosphate is described, crude phosphate being treated with chlorine and/or hydrogen chloride at 600 to 800 DEG C, and the crude phosphate, if required, then being extracted using water.

Description

Process for the separation of heavy metal ions

Rock phosphate Phosphorus-containing fertilizers are often acidic Digestion of phosphorite or apatite produced. Under the action of mineral acid the sparingly soluble tricalcium phosphate of the rock phosphate is decomposed. The calcium salts the mineral acids used must then be separated off in order to remove the to obtain crude phosphoric acid as a product. Metallic substances contained in the rock phosphate Most of the impurities such as cadmium, mercury, lead, thallium and arsenic remain in phosphoric acid. Since this acid is not suitable for all purposes, Numerous attempts have already been made to remove them from undesirable metallic ones To get rid of impurities. For processing raw phosphoric acid into fertilizers However, the test results so far have not offered a technically favorable route so far.

In US Pat. No. 3,133,791 there is a method of separation of iron from rock phosphate described, the rock phosphate at temperatures im Range from 4000C to 1000po with a defined mixture of hydrogen chloride and chlorine is treated.

According to US Pat. No. 2,629,650, iron can be mixed from rock phosphate with hydrogen chloride removed at 3500-4000C.

For the separation of heavy metal elements from the second subgroup of the periodic table such as cadmium and mercury, especially cadmium from rock phosphate no economical process was known up to now. For thermal removal must to use temperatures around 12000C.

So far there are only methods for extraction or

Separation of cadmium from raw phosphoric acid (see Congress report, Cadmium Seminar, p. 6, Nov. 20, 1980 in Rosslyn, Virginia). Cadmium ions are particularly firmly built into the rock phosphate mineral, as they are lattice points of the calcium occupy in the crystal (see congress report cited above).

It has now surprisingly been found that elements of the second Subgroups such as cadmium and mercury are easily separated from rock phosphate can be. The method is characterized in that one with rock phosphate Chlorine or hydrogen chloride or with a mixture thereof at temperatures of 600 to 8000C, in particular 650 to 7500C.

The method is preferably used for separating cadmium.

Chlorine and / or hydrogen chloride can be used for the process according to the invention can be used as such or from compounds added to the rock phosphate be developed during the process, e.g. by adding chlorides and non-volatile mineral acids such as phosphoric acid or their anhydrides, if appropriate in the presence of oxygen or other oxidizing agents such as sodium perchlorate.

This roasting process is carried out in a reactor, with various Reactor types such as fluidized bed ovens, rotary kilns, deck roasting ovens, Hearth roasters, dust roasters, sinter roasters can be used.

In the process according to the invention, chlorine or

Hydrogen chloride, in particular chlorine, is used directly, with one a flow of chlorine and / or hydrogen chloride through the reactor at one flow rate from 0.3 to 3 standard liters / h.cm? directs. The residence times can be between Between 1 and 60 minutes, liable between 10 and 30 minutes. Depending on the reactor type, larger or smaller throughput rates are also possible possible with chlorine or hydrogen chloride.

The rock phosphate can expediently be fed into the reactor in the ground state be supplied, for example in a fineness of 100 - 200 µm grain diameter.

According to the invention, iron (III) chloride is added to the rock phosphate in the range of 1 to 10% FeCl3, based on rock phosphate, before the chlorination is carried out The roasting process is advantageous because the content of the unwanted heavy metal is still present can be further lowered. Obviously, this is not based on a direct one Displacement process of, for example, cadmium against iron ions, as sodium ions are added (in the form of sodium chloride) do not show the effect of iron (III) chloride.

When using chlorine as the reaction medium, instead of Iron (III) chloride also includes other iron compounds such as iron oxides or -sulfates or iron are added in finely divided form.

The method according to the invention can also be used for the separation of lead, Thallium or arsenic from rock phosphate can be used.

After chlorinating roasting, the rock phosphate has a chlorine content from about 1 to 3 8. Since such a chlorine content the further processing of the Rock phosphate for the production of fertilizers by acid digestion according to the Odda process would interfere, an after-treatment of the rock phosphate can be added to the chlorinating roasting connect, this being extracted after cooling with water low in chlorine ions. In general, it is sufficient if the washing process is continued for so long until a chloride content of the rock phosphate of 40.05% is reached. The washing process can be done in a known manner by digestion, slurry, filter or similar. The used water can after separation of the chlorine ions, e.g.

by means of an ion exchanger, returned to the washing process will.

The invention is illustrated in more detail by the following examples.

Example 1 Togo phosphate with a content of 35.5% P205, 50.2% CaO, 1.1% Fe203, 1.18 Al203, 2.2% H2Q and 58 g Cd / g was heated in an electrically Tube furnace, which was equipped with a tube made of quartz glass (35 mm), under the Treated with chlorine conditions mentioned in the following Table I. The cadmium concentrations the samples were determined by atomic absorption.

Table I temp. Dwell chlorine bast content Chloride content des search OC time amount of Cd rock phosphate after the min Nl / h ßg / g roasting 1 595 30 22.5 59 0.35 2 700 30 22.5 5 2.2 3 745 30 22.5 4 2, 4 4 800 10 22.5 7 1.7 5 800 20 22.5 4 2.2 6 800 40 22.5 1 2.5 Nl = standard liters. Example 2 The procedure was as described in Example 1 procedure, but using hydrogen chloride instead of chlorine. The table below 2 shows the test results.

Table II. Temp. Residence Amount of Residual Content Chloride Content of the look for 0C time chlorinated water on Cd rock phosphate for min ßg / g of the Bostung Nl4h.

7 600 30 18.6 43 1.9 8 700 30 18.6 13 2.7 9 795 30 18.6 2 2.9 Example 3 The procedure was as in Example 1, but 10% sodium chloride had been added to the rock phosphate beforehand or 5% iron (III) chloride mixed in. As Table III shows, the treatment performs only in the case of ferric chloride to an improvement in the results: Table III Ver teas. Dwell amount of chlorine Addition of residual content of Cd such ° C time Nl / h NaCl or min N1 / h FeCl3 11 610 30 22.5 NaCl 54 12 800 30 22.5 NaCl 38 13 595 30 22.5 FeCl3 34 Example 4 The raw phosphate was after the chlorinating Roasting, as described in Example 1, washed with distilled water (1: 5), filtered and washed with a little water (2: 1). The chloride content could thus be largely eliminated.

Table IV Ver Te: p. Residual amount of chlorine residual content rock phosphate search ° C min Nl / h of Cd chloride content (%) time cls / s before washing after washing 14 700 20 22.5 n.d. 1.7 -15 795 20 22.5 n.d. 2.1 16 700 20 22.5 15 - 0.05 17 795 20 22.5 6.2 - 0.03

Claims (6)

Claims: 1. Process for the separation of heavy metal ions such as cadmium or mercury from rock phosphate, characterized in that the rock phosphate is treated with chlorine and / or hydrogen chloride at 600 - 8000C and the rock phosphate is then optionally extracted with water. 2. The method according to claim 1, characterized in that the Treatment of the rock phosphate in the chlorine resp. Carries out hydrogen chloride stream. 3. The method according to claim 1, characterized in that the Adding rock phosphate compounds that release chlorine or hydrogen chloride. 4. The method according to claim 1, characterized in that the Rock phosphate mixed with iron or iron compounds before roasting. 5. The method according to claim 1, characterized in that for the chlorinating roasting uses chlorine. 6. Use of rock phosphate for the production of fertilizers according to the Odda process, characterized in that it is done before the acidic digestion subjected to the method according to claims 1-5.