US2031579A - Preparation of phosphates of manganese - Google Patents

Description

Patented Feb. 18, 1936 PATENT OFFICE PREPARATION OF PHOSPHATES OF MANGANESE Charles F. Booth, Anniston, Ala., assignor to Swann Research, Incorporated, a corporation of Alabama No Drawing.

Application April 13, 1933,

Serial No. 665,964

9 Claims. (01. 23-105) 7 This invention relates to a process for the preparation of phosphates of manganese. One

of the objects of this invention is to provide a process for the production of phosphates of manganese from oresv or from alloys of manganese,

whereby the losses of manganese and phosphorus compounds are largelyeliminated. Another object is the provision of a process whereby considerable flexibility is had concerning the type of 10 phosphate finally produced, without sacrifice of purity of the resulting compound and without loss of manganese or phosphoric acid. A still further object is the preparation, in uniformly pure form, of phosphates of manganese; by which 13" term is included the mono-, diand tri-basic phosphates of manganese or mixtures thereof.

Previous methods for preparing the phosphates of manganese have been concerned with the treatment of manganese alloy or of manganese 2o ore with phosphoric acid, followed by crystallization of manganese phosphate. Othermethods mentioned in the literature involve the treatment of rhodochrosite, a natural carbonate of manganese, with phosphoric acid, or the treatment of pyrolusite in similar manner. These methods are unsatisfactory for the present purpose for the reason that the reactivity of these forms of manganese is low, the reaction requiring an excess of acid or a high temperature, and consequently resulting in loss of phosphoric acid and manganese. For these and other reasons, a more eificient method for the production of the phosphates of manganese was greatly to be desired. In conducting experiments to produce the phosphates of manganese from a manganese alloy or ore and phosphoric acid, I have discovered that if I first produce a soluble manganese salt by reaction of an acid withthe manganese source material, I may precipitate a pure insoluble carbonate of manganese which is in such a reactive form that further treatment with phosphoric acid to produce one or more of the manganous orthophosphates is an extremely simple and efficient procedure.

For the purpose of enabling others to practice my invention, I give the following specific example of a preferred means for carrying out my process, with the understanding, however, that 50 my process is not limited to such specific means,

but is susceptible to various changes and modifications without departing from the spirit of my invention.

My process is preferably carried out in three 55 successive steps, which are herein more completely described, together with the variations which are applicable to each step.

Step I This step has for its object the preparation of a soluble manganese compound. For this purpose I react a manganese ore with an acid chosen from the group consisting of hydrochloric, sulfuric, nitric, or, if I am treating a manganese dioxide, I may employ gaseous sulfur dioxide. 10 In the latter case I merely bubble sulfur dioxide gas from a sulfur or pyrite burner through a suspension of manganese dioxide in water, absorption of the gas being almost quantitative and yielding manganese sulphate dissolved in water. 15

If sulphuric acid is available, I may treat either a manganese carbonate ore or a manganese. dioxide ore with the acid, heating, if necessary, to accelerate the reaction. If hydrochloric acid is available, I may react such acid with either the dioxide or carbonate ore, in the former case with the formation of chlorine gas and the production of the manganous chloride in solution. By similar means a ferromanganese alloy may be treated. For most operations I prefer to use sul- 25 furic acid or sulfur dioxide, if the dioxide ore is being treated, merely because of the simplicity and ease of the operation and general availability of the reagents.

By whatever means I employ I obtain, as a product of this first step, a solution of a soluble manganese salt, together with some iron also in solution.

Step II This step has for its object the treatment of 35 the solution obtained in the first step with a soluble carbonate, first for the removal of iron, if present; and, secondly, for the precipitation of manganous carbonate in insoluble form. 40 I have now found that if I add to the manganese solution an alkaline carbonate, by which term I include either the ammonium, sodium or potassium' carbonate, to the point where the said solution has a pH in the neighborhood of 6.1, the iron is selectively oxidizable by means of a current of air. The result of such treatment is to oxidize the ferrous iron to the ferric state, after which it may be quantitatively removed from the solution as the hydroxide. The manganese is unchanged by such treatment. After removal of the iron by filtration, the solution contains the manganous salt in a substantially pure form and, for convenient treatment, should contain about 20% manganese salt in solution.

The solution is then treated with additional amounts of alkali carbonate for the purpose of raising the pH of the solution to the neighborhood of 7.3. At this point the manganese precipitates as a light fiocculent precipitate which is collected on a filter and washed to remove soluble salts. For most purposes, where a lightcolored product is desired, care should be taken not to raise the alkalinity much beyond the abovementioned point. The precipitate is probably a manganese carbonate, a basic manganese carbonate, or a mixture of these. It is treated as follows:-

Step III The filter cake obtained as above outlined, and comprising essentially manganese carbonate, is now treated with phosphoric acid. Because of the reactivity of this form of manganese carbonate, I may now produce either the mono-, di-, or tri-basic manganese phosphate, the particular salt formed depending on the amount of acid used.

If it is desired to produce mono-basic manganese phosphate, the carbonate precipitate is treated with phosphoric acid in the ratio of 2.59 pounds of P205 for every pound of manganese present. An acid containing from 70% to 75% H3PO4 is preferably used.

The production of the di-basic manganese phosphate requires 1.298 pounds of P205 as acid of 7 to 75% H3PO4 content per pound of manganese, while the tri-basic compound requires 0.862 pound of P205 as acid of 70% to 75% strength per pound of manganese. For mixtures of compounds intermediate between these compounds, a corresponding proportion of acid is required.

If strong phosphoric acid is available, little or no drying of the acidified product is necessary. This feature is particularly valuable if the monobasic phosphate is to be produced. Such a phosphate is water-soluble and, when ordinarily produced in solution, it is necessary to crystallize the mono-basic phosphate from an acid solution, because of hydrolysis of this phosphate in solution.

If the dibasic or the tribasic phosphate is to be formed, the reaction of the manganese carbonate with the phosphoric acid may be carried out either by direct mixing of the strong acid and manganese carbonate, or the latter compound may be suspended in water and dilute phosphoric acid added in the required proportion.

A further advantage in the use of strong phosphoric acid, when treating the manganese carbonate precipitate in the absence of an excess of water, follows from the fact that with the proper choice of acid a dry product is formed after reaction. This is due to the fact that all of the manganous orthophosphates form hydrates. Thus the monobasic manganous phosphate crystallizes with two molecules of water, the dibasic with three molecules, and the tribasic with seven molecules of water. I have found that such hydrates form directly after the precipitate has reacted with the acid, the final product being a dry, light-colored powder. This is an important feature of my process, since it enables a dry hydrated crystalline product to be produced directly by mixing, and obviates the necessity of crystallizing the phosphate from a water solution and then drying the product.

Theoretically, the production of the. monobasic manganese phosphate requires a higher concentration of acid than that indicated; however, I

have found that the heat liberated on neutralization is so much greater that a considerable amount of water is evaporated, the product being substantially dry.

A particular advantage following from the use of the carbonate for the production of the phosphates is that the liberated carbon dioxide has a marked capacity for carrying with it a substantial amount of water vapor, thus aiding in the production of a dry product.

What I claim is:-

1. Process for the production of light colored manganese phosphates comprising first forming a soluble manganese compound in solution, treating said solution with an alkali carbonate to yield therein a pH of substantially 7 .3 and to precipitate a basic carbonate of manganese, and then treating said carbonate precipitate directly with phosphoric acid in amount sufficient to form dry phosphates of manganese.

2-. Process for the production of a mono-basic manganous phosphate, comprising first forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to yield therein a pH of substantially 7.3 and to precipitate a manganese compound, removing. said manganese compound from solution and directly reacting said compound with phosphoric acid in amount sulficient to form therewith dry monobasic manganous phosphate.

3. Process for the production of dibasic manganous phosphate, comprising forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to produce therein a pH of substantially 7.3, and precipitate therein a light-colored manganous compound, removing said manganous compound from solution and reacting said compound with phosphoric acid in amount sufficient to form therewith a dibasic manganous phosphate.

4. Process for the production of tribasic manganous phosphate, comprising forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to produce therein a pH of substantially 7.3 and precipitate therein a light-colored manganous compound, removing said manganous compound from solution and reacting said compound with phosphoric acid in amount sufficient to form therewith a tribasic manganese phosphate.

5. Process for the production of manganese phosphates, comprising first forming a soluble manganese compound in solution, treating said solution with an alkaline carbonate to obtain therein a pH in the neighborhood of 6.1, oxidizing the iron which may be present, removing said oxidized iron compounds from said solution, then further treating such solution with additional amounts of alkaline carbonate to precipitate the manganese as carbonate, removing said manganese carbonate from the solution and treating said precipitated carbonates with phosphoric acid.

6. Process for the production of manganese phosphates, comprising first forming a soluble manganese compound in solution, treating said solution with an alkaline carbonate to obtain therein a pH in the neighborhood of 6.1, oxidizing the iron which may be present, removing said oxidized iron compounds from said solution, then further treating said solution with an alkaline carbonate to obtain therein a pH in the neighborhood of 7.3 to precipitate the manganese, removing said manganese precipitate from solution and treating said precipitate with phosphoric acid.

7. Process for the production of a monobasio manganous phosphate, comprising first forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to obtain therein a pH in the neighborhood of 6.1, oxidizing the iron which may be present, removing said oxidized iron from solution, then further treating said solution with alkali carbonate to obtain therein a pH in the neighborhood of 7.3 and thereby to precipitate a manganese compound therefrom, removing said manganese precipitate from the solution, and treating said precipitate directly with phosphoric acid.

8. Process for the production of dibasic manganese phosphate, comprising first forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to obtain therein a pH in the neighborhood of 6.1, oxidizing and removing any iron which may be present, then further treating said solution with alkali carbonate to obtain therein a pH in the neighborhood of at least 7.3 and thereby to precipitate a manganous compound therefrom, removing said manganous precipitate from solution and treating said precipitate directly with phosphoric acidto form therewith dibasic manganous phosphate.

9. Process for the production of tribasic manganese phosphate, comprising first forming a soluble manganous salt in solution, treating said solution with an alkali carbonate to obtain therein a pH in the neighborhood of 6.1, oxidizing and removing any iron which may be present, then further treating said solution with alkali carbonate to obtain a pH in the neighborhood of 7.3 and thereby to precipitate a manganous compound therefrom, removing said manganous precipitate from solution and treating said precipitate directly with phosphoric acid to form therewith tribasic manganous phosphate.

CHARLES F. BOOTH.