Chemistry of inorganic compounds – Phosphorus or compound thereof – Oxygen containing
Patent
1984-01-05
1985-06-18
Heller, Gregory A.
Chemistry of inorganic compounds
Phosphorus or compound thereof
Oxygen containing
423167, 423311, 423319, C01B 1516, C01B 2526
Patent
active
045240540
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the beneficiation of phosphate ores, and in particular to the beneficiation of low-grade phosphate ores.
As deposits of good quality phosphate rock are becoming exhausted, increasing attention is being given to the potential of the abundant deposits of lower phosphate content rock as a source of phosphate fertilizers and the like. Unfortunately it is found that in addition to yielding less phosphate, such rock often contains impurities which give rise to problems not encountered when processing higher-grade material. For example, when the sulphuric/phosphoric acid digestion process for producing superphosphate is applied to a low-grade, high silica-content rock, the inert gangue introduced by the impurities gives a superphosphate product which has a reduced phosphate content, and hence requires higher transport and distribution costs, when compared to superphosphate made from higher grade materials.
In addition, the conventional sulphuric/phosphoric acid processes required the production of sulphuric acid from sulphur dioxide which in turn is derived from brimstone, smelter off-gases or some other source of sulphur.
With a view to avoiding the aforesaid problems, we have investigated the leaching of phosphate ores with mixtures comprising water, sulphur dioxide (SO.sub.2) and an organic carbonyl compound such as acetone. It is well known that admixtures of this type give rise to an hydroxysulphonic acid, according to the equation: ##STR1##
As a result of the enhanced SO.sub.2 activity and hydroxonium ion concentration the leachant readily takes up the phosphate values from the ore, but silica and other impurities, such as iron, aluminium and fluorine remain virtually unaffected.
U.S. Pat. No. 4,113,842, assigned to the Tennessee Valley Authority (TVA), describes the use of hydroxysulphonic acid leachants in preparing dicalcium phosphate from phosphate ores. In the process described in this patent, dicalcium phosphate is taken into solution during leaching but calcium hydroxysulphonate, which is formed at the same time, is separated as a solid along with unreacted gangue. When the process is operated in this way, the presence of calcium hydroxysulphonate causes the leach slurry to become thixotropic. The consequences of this are that the efficiency of leaching is seriously reduced, and, when the solids are separated from the leach liquor by filtration, the retention of a large amount of mother-liquor by the solids makes it difficult to wash the filter-cake economically. Moreover, while the calcium hydroxysulphonate may be treated for recovery of the SO.sub.2 and the carbonyl compound by thermal decomposition, because the sulphonate is precipitated at the leaching step, as taught in the TVA patent, the recovery step becomes energy inefficient because the inert gangue as well as the sulphonate has to be heated to the required temperature. It will be appreciated that with low-grade ores, which in some instances may yield nearly 50% inert residue, such a process could result in a significant energy wastage.
We have now found that by careful control of leaching conditions it is possible to keep the calcium hydroxysulphonate in solution during leaching and thus defer precipitation of calcium until a stage in the process which is technically and economically more advantageous.
Accordingly, in its broadest aspect this invention provides a process for the recovery of phosphate values from a phosphate ore, wherein the ore is leached with a mixture comprising water, sulphur dioxide and an organic carbonyl compound, under conditions such that substantially no calcium hydroxysulphonate is precipitated.
Suitable carbonyl compounds are ketones and aldehydes such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetaldehyde, formaldehyde and substituted and unsubstituted benzaldehydes.
Our investigations have shown that calcium hydroxysulphonates have a limited solubility in the reaction mix and their solubility is dependent upon factors such as calcium ion concentration, ca
REFERENCES:
patent: 4113842 (1978-09-01), McCullough et al.
patent: 4238459 (1980-12-01), Phillips et al.
George Christopher W.
Sinha Hari N.
Vujcich Mary R.
Walker Graham S.
Commonwealth Scientific and Industrial Research Organization
Heller Gregory A.
Queensland Phosphate Limited
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