BE484283A - - Google Patents

Description

       

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    Improvements relating to the purification of minerals.



   The object of the invention is the purification of minerals, especially siliceous materials, for example silica sands, quartzites, quartz rocks, gravels, sand stones, but also other minerals such as fluorspar, feldspar. and alumina.



   Reducing the content of certain impurities, especially iron and chromium compounds, is important for certain purposes.

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   For example, these impurities in the silica sands used for the manufacture of colorless glass, give a harmful coloring to the glass. This discoloration can be partially suppressed or masked by the addition of various materials, for example arsenious oxide or antimony oxide and metallic selenium with cobalt oxide, but this process becomes less efficient at as the impurity content increases.



   For good quality colorless glass containers the sands should contain no more iron than 0.03% Fe2O3 and no more chrome than 0.0005% CrO. For the highest quality tableware, suitable sands should not contain more iron than equivalent to 0.010 to 0.015% Fe2O3, with a chromium content equal to or less than the amount / corresponding to 0 , 0002% Cr2O3.



   The main object of the present invention is to effect a considerable reduction in the iron oxide content of the mineral in a suitable manner.



   Of the silica sands, crushed rocks, etc., which are now available, only a relatively small proportion corresponds to the above specifications of the sands for the manufacture of colorless glass containers or high quality colorless tableware.



   Among the methods previously proposed for the purification of siliceous sands or the like, the following methods may be mentioned:
1) Treatment with strong acids, with or without heating, at atmospheric pressure ... or at high pressure, to remove iron oxide.



   2) Sand screening with sodium chloride followed

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 water leaching.



   3) Treatment of the sand by passing it through perforated plates in a tower, against the current of ammonium chloride and dry air at approximately 500 ° C., the reaction gases being conducted in water. Iron is removed carefully, a form of volatile ferric chloride.



   4) The sand can be washed with an aqueous solution of sodium carbonate, or sodium sulphide, or else with detergents such as sodium hexametaphosphate, tetrasodium pyrophosphate, etc. in aqueous solution, with or without carbonate sodium.



   5) The washed silica sand can be treated with a solution containing 15% sulfuric acid and 5% ferrous sulphate at a temperature between 80 and 100 C; or
6) The sand can still be treated with a solution. aqueous containing a small amount of acid oxalate or quadroxalate, and a small amount of crystallized ferrous sulfate (not more than about half the amount of acid oxalate or quadroxalate). The treatment is carried out with the hot solution considerably below the boiling point, and preferably at a temperature between 80 F and 120 F.



   7) It has been proposed to treat sands, etc. with dilute solutions of sulfate or titanium chloride, and a fluorine compound, such as, for example, hydrofluoric acid, sodium fluoride or sodium fluosilicate.



   Among the various methods currently available, some of which are outlined above, are some / hardly applicable on an industrial scale, some are expensive and some can only be successfully applied to isolated sands. In some of the pro-

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 ceded cited and which can be applied industrially, it is necessary to use temperatures well above the normal temperatures of the atmosphere. or .: use of very corrosive chemicals; each of these two conditions results in an increased cost price or greater difficulty in handling.



   The use of hydrofluoric acid in particular is dangerous, the acid is difficult to handle, is expensive and highly corrosive. Due to its well known ability to attack siliceous materials, it should not be expected.
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 dre that the I! 1.c1c1l ') hydrofluoric 11U: tno Qf'f'AO t:!. vempnt, be replaced by other acids.

   However, it has now been shown that an aqueous solution of titahous chloride and oxalic acid is remarkably effective in the removal of iron compounds in particular, and to a great extent also of other impurities such as iron compounds. chrtme compounds. It has furthermore been proved that less satisfactory results are obtained if the oxalic acid part of the above mixture is replaced by one or more of the following compounds: formic acid, tartaric acid, sodium acid oxalate; chlorydric acid, sulfuric acid, acetic acid, ferrous sulfate and hydrazine sulfate.



   It has also been proven that for the treatment of certain sands, the titanous chloride part of the titanous chloride-oxalic acid mixture can be replaced by titanium sulphate although this salt is generally not as effective as the chloride, but with certain sands sulphate even gives better results than chloride.



   The concentration of the solution is normally between 0.1 and 5% titanium chloride or sulphate,

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 with a variable oxalic acid concentration between analogous limits. Certain English sands can be treated well with solutions containing 1% titanium chloride with 1% oxalic acid.



     The titanous chloride-oxalic acid solution may advantageously contain moisturizers or detergents by which intimate contact between the chemicals and the surface of the individual sand grains can be provided. In this way, the coating or the iron soils can even be attacked more quickly and more completely.



   Additions of other acids or salts to the titanium salt-oxalic acid solution, for example sulfuric acid, hydrochloric acid, sulfate or sodium chloride, in similar concentrations additionally produce a slight improvement in the purity of the sand produced.



   The treatment is normally carried out at atmospheric temperatures, and the process is thus considerably simplified. If, however, certain sands require it, the chemical action can take place at higher temperatures, up to but without reaching 100 C.



   To obtain the most effective chemical action on the coating of impurities, intimate contact between the grains of sand and the chemical solution must be maintained by kneading, mixing, riddling and other intimate agitation. Reaction apparatus must perform this mixing efficiently and may include barrels, rotating apparatus (vertical, inclined or horizontal) or friction scrubbers and / or centrifugal pumps. To minimize the oxidation of chemicals, residual air should be excluded and the entry of any additional air during chemical sand treatment should be avoided. Nitrogen or another inert gas

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 any one can be used to exclude air and avoid this atmospheric oxidation.



   Reaction apparatus must be constructed so as to satisfy these minimum oxidation conditions.



   All devices, pumps, etc. are made of material or materials resistant to the action of the chemical solutions used. They must be incapable of introducing into the sand any harmful impurity, such as iron or chrme. Among other materials, it has been proven that certain stainless steels have suitable properties.



   The precise duration of contact between the grains of sand and the solution of titanium chloride or sulfate and oxalic acid should be chosen so as to suit the particular sand being treated, and depends on the concentration of the chemical solution, relative proportions of sand and solution used, the temperature of the operation, and the vigor with which the washing or washing is carried out. The contact time does not exceed, under normal conditions, a few minutes.



   It has been proven that titanium salts can be recovered from the titanium state and regenerated to the original titanium state by well known methods such as colui carried out in a zinc-mercury amalgam reducer tower. (Jones), or by using a cadmium reducing tower, the cadmium being present in the form of fine particles, or else by applying an electrolytic method such as that used for the industrial preparation of titanium salts.



   In the process of the invention for the treatment of sands or similar products by chemical means, it is proposed to make full use of these recovery systems.

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 and reclamation, or others, by choosing the reclamation method appropriate to the chemical combination adopted for treating the sand. Thus, if the recommended mixture of titanium chloride or sulfate and oxalic acid is used, an electrolytic recovery system will be used.

   It has been proved that the titanium solution should have sufficient acidity, of about 1% by volume of hydrochloric acid when titanous chloride is used (0.3% by volume of sulfuric acid when titanium chloride is used. uses sulfate) if reduction is to be rapid and efficient; a filter system is also essential.



   When the silica sand or the like has undergone the chemical treatment forming the object of the present invention, it is successively subjected to operations of separation from the solution, washing with water and dehydration.



   At the stage of separation of the solution, any excess of the chemical solution (which may contain reaction products with the soils or ferrous coatings or containing the chrism of the grains of sand) can be separated from the grains of sand.



     In the second water wash stage, all reaction products are effectively washed away from the "cleaned" sand grains, and the washing operation continues until the "cleaned" sand grains. clear water remains in contact.



   On the third stage (dehydration), "clean", wet grains of sand are released from the clear water in tact, producing "clean", practically dry grains of sand.



   It has been proven that for the first and third of these stages, solution separation or dehydration can be carried out successfully by central force.

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 trifuge. By this means, up to 98% of the chemical solution can be recovered. The centrifugal apparatus, which may be of the continuous or non-continuous type, is constructed of a material or materials which are not attacked by the chemicals employed, and which do not produce any appreciable amount of iron or chromium impurities.



   The equipment used on the second stage, for washing with water, must effectively separate the two phases, that is to say the "clean" grains of sand and the impurities containing iron and chromium; the apparatus must ensure that each grain of sand is effectively surrounded and washed by water. A backwashing machine meets these conditions.



  In no case should impurities be allowed to return to the cleaned grains of sand; if dewatering devices are used to reduce the moisture content of the purified sand before placing it in gear, trucks, spandrels, etc., the cleaned sand should not be allowed to act as a filter for the water contaminated wash.



   The mineral, prior to treatment with the solution in accordance with the present invention, should be washed well with water and preferably be treated by well known methods for removing heavy minerals, for example methods using mine separation tables.



   The examples which follow demonstrate the effectiveness of the process in rendering sands of questionable qualities suitable for the production of colorless glass. In the data given, care has been taken, in order to avoid the confusion often existing in examples given in older patents, or in the scientific literature, to attribute to the chemical process improvements which are due or can be made by washing with water alone. It is only by avoiding such confusion that the value of the chemical process can be properly appreciated.



   In the numbers given in the paragraphs that @

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 Following, Inaction of purification of the proceeding on the sand which has been washed with water, and from which the heavy minerals have already been removed, is clearly demonstrated. Washing with water removed the clay; mud and poorly adherent plaster; the separation of heavy minerals removed yet another
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 source of iron impurity (..1. the Clll'OJ, 1e).

   The acuion of the nr'uv "to the chemical process on the plaster or the ferrous soils adhering strongly to the sand chips is thus reflected in a precise manner.



   The following experiments show the advantage of using the solution corresponding to the present invention compared to other solutions.



   Trials on English yellow sand.



   Coarse sand ............ 0.090% FeO
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 After vigorous washing with water 0.07i $ 1 Fe :: P3 After separation of minerals: heavy 0.054% Fe2O3.



    All tests were carried out using solutions
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 t 1 ... i is exposed s a; 1x c v i> to 1 L J, i; > i at [no [jl) lL6l'i (luo ;.
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  Aqueous <SEP> solutions <SEP> containing <SEP>: <SEP>% <SEP> Fe203 <SEP>% <SEP> Fe2O3
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<tb> removed <SEP> final
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<tb> 1% <SEP> TiCl3 <SEP> 0.015 <SEP> 0.039
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<tb> 1 <SEP>% <SEP> (COOH) 2 <SEP> 0.013 <SEP> 0.041
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<tb> 1% <SEP> TiCl3 <SEP> + <SEP> 1% <SEP> (COOH) 2 <SEP> 0.034 <SEP> 0.020
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 1% TL (; :) 4) 2. -t- 1% (COOiï) 2 0.039 0.015 0.25% TiC13 0.01 0.042 O; à513 TiCl3 + 0.25% (C00 = :) 0, (82 0.03 Analogous experiments made using 1% of
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 Cl10iUi, ii, e titanium and 5 "E formic acid or 1% of any of the following;

   tartaric acid, acid oxalate

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 sodium, sulfuric acid, acetic acid, ferrous sulfate and hydrazine sulfate gave 0.031 to 0.037% FeO in the final product.



   Likewise, analogous experiments were carried out using the titanium salt-oxalic acid solution and an additional acid or salt with the following advantageous results:
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 Tests on sand Untreated sand 0.090% Fe2O3 Sand after vigorous washing with water 0.0071% Fe2O3 Sand after vigorous washing with water and separation of heavy minerals 0.054% Fe2O3
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 Aqueous solutions used F 0 3 Fe 2 0 3 removed from in the sand final sand 1% titanous chloride + 1% oxalic acid 0.042 0.012 + 1% sodium sulfate
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 19 titanium chloride + 1% oxalic acid + 1% sodium chloride 0.041 0.013 1% titanium chloride + 1% oxalic acid + 1% sulfuric acid 0.040 0,

  014 il / titanous chloride ¯ 1% oxalic acid + 1% hydrochloric acid 0.038 0.016
An installation for the application of the process can
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 corlBi: Jtl 'ewaent1elluIllent un / llJvnre1l du: Lc.LVCic ù l' U'LlI) followed by a mine separation table having a series of ribs above which water flows, entraining sand particles released heavy minerals to a collecting member then by a conveyor and a storage hopper, in a centrifugal dehydration machine.



  A bucket chain or other elevator then transports the sand to a storage hopper from where it is introduced.

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 in a rotating envelope of polyonal cross section in which the sand is contacted with the chemical solution described above. The mixture then falls into a hopper which feeds it to a centrifugal solution separation machine, from where it falls onto a distributor cone in an upwardly directed tangential jet vortex washer. The sand is then taken by a conveyor and a hopper and transported to a centrifugal dewatering machine and is finally transferred to a storage hopper.



   CLAIMS.



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1.- Process for the reduction of ferrous impurities in minerals, characterized in that it comprises the treatment of the mineral with an aqueous solution of a chloruretitanium or titanium sulfate and oxalic acid.


    

Claims (1)

2. - Process according to claim 1, characterized in that the solution contains between one tenth percent and five percent of each of the two specified ingredients. 3. - Process according to claims 1 and 2, charac- terized in that the solution also contains an additional acid or salt. 4. A process according to claims 1-3, characterized in that a wetting agent or detergent is added to the solution. 5. - Process according to claims 1-4, characterized in that the mineral is treated with the solution in a non-oxidizing atmosphere during sufficient mixing of the mineral and the solution. 6. - Process according to claims 1-5, characterized in that the mineral, after treatment with the solution <Desc / Clms Page number 12> EMI12.1 cit6 (3, u., L Cel1'Ll'i1'ugé) pul ...; iuved with water and then centrifuged again. 7. A method according to claim 3, characterized in that the additional substance is sulfuric acid or hydrochloric acid. 8. - A method according to claim 3, characterized in that due the additional substance is sodium sulphate or sodium chloride. 9. A process for the reduction of ferrous impurities in minerals substantially as described.