FR2519959A1 - Extn. of phosphate(s) from minerals and concentrates - by ammonium hydrogen sulphate treatment and total recovery of sulphate(s) - Google Patents

Abstract

Minerals and concentrates containing apatitic phosphates are treated to recover the P2O5 they contain by the following process: (a) the mineral or concentrate is leached with aqueous NH4H2O4. (b) Optionally excess hydrogen sulphate is neutralised. (c) The product from (a) and (b) is filtered to give a first filtrate and a filter cake of gypsum, CaCO3, and insoluble impurities. (d) Sulphate is recovered from the filter cake of (c). (e) The product from (d) is filtered to give a second filtrate, comprising ammonium sulphate and calcium carbonate part of which may be used in step (b) or to generate CO2 used in step (d), the rest being rejected. (f) The first filtrate from step (c) is treated with ammonia and (g) it is filtered to give a third filtrate, comprising ammonium hydroxide which is used in step (d), and a filter cake of triammonium phosphate. (h) The filter cake from (g) is dried to give NH3 which is used in steps (d) and (f). (i) The dried product from (h) is granulated, to give the desired mono- and di-ammonium phosphates. (j) The second filtrate from step (e) is submitted to a crystallisation, and the product dried to give dry ammonium sulphate which is (k) heated to effect thermal decomposition with formation of ammonium hydrogen sulphate and liberation of ammonia that isused in step (d) and (f), together with the ammonia from step (h). (l) The ammonium hydrogen sulphate from step (k) is used in step (a). The process gives good recovery of soluble phosphates without loss of the sulphates necessary to bring about solubilisation. There is no costly thermal treatment and no evaporation of large quantities of water.

Description

 The present invention relates to the recovery and recovery of P205 contained in ores or concentrates of phosphates, and more particularly in ores or concentrates of phosphates not usable for the production of phosphoric acid wet. P205 is recovered in a form of P205 soluble water, namely in the form of ammonium phosphates.

With regard to the recovery of phosphates, it should be recalled that
- The preparation of complex fertilizers from phosphate ores is largely through the production of phosphoric acid. This is obtained by sulfuric attack of the raw ore or, more frequently, a concentrate prepared by physical processes of enrichment.

- the sulfuric attack requires, if it is to be carried out under technically and economically acceptable conditions, that the treated product contains limited contents in some of the impurities which are frequently associated with phosphates and the most important of which are certainly dolomite, calcite, and minerals bearing iron or aluminum. In addition, it consumes a large amount of sulfur, corresponding to the sulfur released into the process, in the form of gypsum which, forming at a rate of about 4 tons of gypsum per tonne of
P205 produced represents a large part of the cost price of the acid produced and causes this cost price to rise unduly.

 - a very large number of ores are not even valorizable by this way.

 It was eminently interesting to have another way of chemical treatment of ores or concentrates of phosphates. It was even more interesting that this route could provide fully soluble P205 water and especially that sulfur losses be reduced to a minimum.

 One of the proposed ways to address this problem was to leach the phosphates, not with sulfuric acid but not with ammonium bisulfate. However, the most recent methods described in the literature relating to this technique allow only a recovery of ammonium phosphate mixed with ammonium sulfate, and result in a sulfur consumption which remains too high, as well as obtaining a fertilizer less interesting than pure ammonium phosphates and the need to evaporate, during the process, significant quantities of water.

 Thus, according to a recent review of the procedures proposed for solubilizing P 2 O 5 of apatitic phosphates by ammonium bisulfate made by M. HUSSIEN (Chem Econ.

 Engng. Rev., October-November 1979, vol. 11, No. 10/11, pp.

47-51), these methods involve
1. phosphate attack by ammonium bisulfate,
2. the regeneration of ammonium bisulfate.

phosphate attack by ammonium bisulfate is consistent with the overall reaction

3 Ca804.2H20 and leads to the production of two water soluble forms of P205 namely monoammonium phosphate and diammonium phosphate, which are two forms of NP fertilizer very popular. This monoanionic phosphate and diammonium phosphate are recovered after ammoniation of the filtrate and drying. The calcium contained in the phosphated elements is eliminated in the form of gypsum during this reaction, as is the calcium present in the form of carbonate which is also attacked according to reaction

Regeneration of ammonium bisulfate is carried out by treating the gypsum (recovered by filtration at the end of the previous etching step with ammonium bisulfate) with ammonia and carbon dioxide, in aqueous suspension; Ammonium sulphate is thus formed, as well as precipitated calcium carbonate, which is the form in which calcium is rejected, depending on the overall reaction that can be written

To regenerate the ammonium bisulfate, it is then necessary to heat the sulphate obtained in solution, after evaporation of the water, until about 350-4500C to realize the reaction.

 In theory, such a process would not result in sulfur consumption.

 Although several versions of this basic scheme have been proposed, essentially different by the attack conditions (use of bisulfate alone or in mixture with (NH4) 2SO4 or with sulfuric acid, different treatment media and temperature, c that is to say pulp and variable temperatures between 90 and 1500C, or solids and temperatures between 450 and 515 0C rotating furnace, as described in US Patent 2,750,270, the method thus defined, although it also includes certain advantageous features, requires two stages of evaporation and drying (of the aqueous solution resulting from the leaching of the ore and the ammonium sulphate solution resulting from the leaching of the gypsum) and a heat treatment step in the vicinity of 5000C for carry out the decomposition of ammonium sulphate into bisulfate.

 In addition, this process leads to the recovery of ammonium phosphate in admixture with ammonium sulfate.

In addition, becoming. Impurities other than carbonates and their influence on the process have not been taken into consideration, although this is a very important problem since a process of this type would be of particular interest for the treatment of ores. or non-recoverable concentrates by the conventional way of producing phosphoric acid.

 A clear need therefore existed for a process which makes it possible to valorize ores or phosphate concentrates and which, while leading to high levels of solubilization of P 2 O 5 and to obtaining pure ammonium phosphates, does not interfere with or practically no sulfur consumption and no longer requires the need for expensive heat treatments and the evaporation of large quantities of water.

 We have now developed according to the invention a method to achieve all these objectives, as well as others that may appear in the light of the description which follows.

The process according to the invention relates to the recovery of P205 contained in ores or phosphate concentrates by solubilization of apatitic P205 with ammonium bisulfate in aqueous solution, and is characterized in that it comprises the combination of the following steps
a) addition to the ore or phosphate concentrate of an excess of aqueous NH4HSO4 solution and leaching,
b) possible neutralization of excess bisul
ammonium fate,
c) filtration of the product of step a) or b) to obtain a first filtrate and a filter cake formed of gypsum, CaCO 3 and insoluble impurities of phosphate,
d) recovering the sulphate from this filter cake,
e) filtration of the product of step d) to collect a second filtrate, essentially formed of (NH4) 2SO4, and calcium carbonate, part of which can be introduced for neutralization in step b) or to regenerate CO2 introduced then in step d>, while the rest is reissued,
f) ammoniation of the first filtrate, resulting from the step
g) filtration of the product of this ammoniation, to form a third filtrate, consisting essentially of NH 4 OH which is sent to step # and a filter cake mainly composed of triammonium phosphate,
h) drying the filter cake of step g to obtain a dried product and NH3 which is used by distributing it between steps d) and fj, while introducing a booster of CO2 in step 9
i) granulation of the dried product of step h), which makes it possible to obtain the desired di- and monammonium phosphates,
j) recovering the filtrate from step e), which is subjected to crystallization and drying, thereby obtaining a dry (NH 4) 2 SO 4,
k) thermal decomposition of (NH4) 2SO4 in step j with formation of NH3 which is added to the NH3 produced in step h) to distribute it between steps d) and and NH4HS04.

 1) preparation of a suitable aqueous NH4HSO4 solution by adding water to the NH4HSO4 product in step k; and using this solution for step a1.

 The single figure of the attached drawing board represents a simplified diagram of this process and should be referred to, if necessary, for a better understanding of the enchainement of the steps between them.

This process combines and combines in an original way a number of known operating phases and
new operating phases.

Thus, among the above-mentioned steps of the process according to the invention, step a) can be carried out with a molar excess of 1 to 2, ie an excess of from 0 to 100%, and preferably from about 50%, of NH4HSO4, while that, which consists of eliminating excess ammonium bisulfate
(step M) is a neutralization step, for which it is appropriate to use calcium carbonate; this step allows the precipitation of the sulphate to the state of gypsum, according to the reaction

 In practice, it may be desirable to plan to add too. an acid (such as H2SO4, H3PO4, etc.) in this step of neutralizing the excess ammonium bisulfate, because the pH increases during the course of the neutralization reaction and it is therefore necessary to limit this phenomenon so that the Neutralization reaction can be done with a sufficient degree of advance.

 Step e) may advantageously include treating at least a portion of the formed calcium carbonate to regenerate CO 2 to be subsequently introduced in step d) and to form CaO which is rejected. This treatment can be carried out in a lime kiln.

 The ammoniation step f) of the first filtrate resulting from the above step, which allows the recovery of the P 2 O 5 contained in the solution obtained after filtration of the gypsum, advantageously consists of an ammoniation of this diluted solution with optional washing. the cake, limited so as to maintain a P205 content of the order of 3.5% or more; this ammoniation is preferably conducted to a pH of about 10.5-11 and leads to a precipitation of P205 in the form of triammonium phosphate (GAP) in substantially quantitative proportions.

 Step j may be, if desired, supplemented by a sulfuric acid feed, in order to compensate for sulfur losses if there are any.

The actual implementation of the method according to the invention on a particular ore is within the reach of those skilled in the art which takes into account the above teachings and which seeks to solve with its own knowledge the industrial problems that are, essentially
the filterability of the gypsum supplied in the leaching reactor and in the neutralization reactor: this is an element on which the quality of the overall result of the process depends; it is linked on the one hand to the operating conditions and on the other hand to the presence of certain impurities and their fate during leaching (ferrous impurities, in particular);
the filterability and the nature of the ammonium phosphates precipitated in the ammoniation reactor: here again the presence of certain impurities contained in the solution plays a significant role in the quality of the overall result; in particular, ferrous impurities, which precipitate as complex phosphates at lower pHs than triammonium phosphate, lead to the formation of P205-soluble citrate, but insoluble water.

 the filterability of the calcium carbonate formed during the recovery of the sulphate.

 Finally, those skilled in the art must take into account, for the optimization of the process, in operation on a continuous industrial scale, ammonia, CO2, P205 and sulfur budgets.

The determination of the optimal operating conditions must be made for each ore to be treated,
using techniques involving routers
and a methodology within the reach of those skilled in the art.

As long as it is properly implemented
in the case of ore or concentrate
phosphates that the technician has to deal with, for the valori
ser, the method according to the invention makes it possible, with respect to
previously described processes
recovery of P 2 O 5 in the form of a much purer ammonium phosphate,
- a lower energy consumption associated with this recovery, and
- effectively total recycling of sulfur.

Claims (6)

 1. Process for the recovery of P205 contained in ores or phosphate concentrates by solubilization of apatitic P205 with ammonium bisulfate in aqueous solution, characterized in that it comprises the combination of the following steps  a) addition to the ore or phosphate concentrate of an excess of aqueous NH4HSO4 solution and leaching,  b) possible neutralization of excess ammonium bisulfate,  c) filtering the product of step a) or b) to obtain a first filtrate and a filter cake formed of gypsum, CaCO 3 and insoluble impurities of phosphate,  d) recovering the sulphate from this filter cake,  e) filtering the product of step d) to collect a second filtrate, essentially formed of (NH4) 2SO4, and calcium carbonate, a portion of which can be introduced for neutralization in the bizou step to regenerate CO2 introduced thereafter in step G while the rest is reiterated,  f) ammoniation of the first filtrate, derived from step cg) cg) filtration of the product of this ammoniation to form a third filtrate, consisting essentially of NH40H that is sent in step dJ and a filter cake composed mainly triammonium phosphate,  h) drying the filter cake of step 9 to obtain NH3, which is used by distributing it between steps d1 and f ;; while a booster of CO2 is introduced in step d) and a dried product,  i) granulation of the dried product of step h), which makes it possible to obtain the desired di- and monammonium phosphates,  3) recovery of the filtrate of step e ;; crystallization and drying, thus obtaining a dry (NH4) 2SO4,  k) thermal decomposition of the (NH4) 2SO4 step with formation of NH3 that is added to the NH3 produced in step h) to distribute it between steps d) and f / ie NH4HS04,  1) Preparation of an appropriate aqueous solution of NH4HS04 by adding water to NH4HS04 produced in step k) and using this solution for step a).  2. Method according to claim 1, characterized in that in step aS an excess of NH HSO is used.  4 to 100%, preferably about 50%.  3. Method according to claim 1, characterized in that one carries out optionally step bzde neutralization mpyen calcium carbonate.  4. A process according to claim 1, characterized in that step f) is implemented for the recovery of the P205 contained in the solution obtained after filtration of the gypsum and consists of an ammoniation of this solution diluted in P205, with washing of the cake limited so as to maintain a P205 content of the order of 3.5% or more.  5. Method according to claim 4, characterized in that the ammoniation is conducted to a pH of about 10.5-11.  6. Method according to claim 4, characterized in that the ammoniation is completed by washing the cake li mity so as to maintain a P205 content of the order of 3.5% or more.