Abstract Utilization of sludges consisting substantially of insoluble aluminum and iron phosphates, of the type obtained by neutralization of crude phosphoric acids produced from wetprocessed phosphate ores. The sludges are combined with silicic acid-containing compounds, which are added in a quantity one or two times the quantity stoichiometrically needed to produce alkali metal aluminum silicates of the general formula Me2Al2SiO6, in which Me is an alkali metal, and with an alkali liquor, which is added so as to obtain an alkali metal oxide: P2O5-molar ratio between 4.0 and 5.0; the resulting suspension is heated to a temperature higher than 90* C., for a period between 30 and 200 minutes, with agitation; phosphoric acid is added so as to produce an alkali metal oxide: P2O5-molar ratio between 2.5 and 3.5; the P2O5-concentration in the resulting solution is reduced down to six to 10 weight percent by the addition of water or recycled wash solution; the solution is filtered; an insoluble residue consisting of Fe(OH)3 and Me2Al2SiO6 is washed out; and the filtrate is used for making alkali metal phosphates.
The process of claim 1, wherein the phosphoric acid added to the suspension is impure wet process phosphoric acid.
Claim 2
Dependent Claim
16 words
The process of claim 1 wherein the said silicic acid-containing compound consists of kieselgur or waterglass.
Claim 3
Dependent Claim
53 words
The process of claim 1, wherein an alkali metal hydroxide is added to the filtrate to establish an alkali metal oxide: P2O5-molar ratio between 3.5 and 4.5 therein, the resulting solution is cooled down to a temperature lower than 30* C., and trialkali metal phosphate which precipitates is separated from the mother liquor.
Claim 4
Dependent Claim
24 words
The process of claim 4, wherein mother liquor which remains after separation of the trialkali metal phosphate is recycled for wet-processing of phosphate ore.
Claim 5
Dependent Claim
18 words
The process of claim 4, wherein the trialkali metal phosphate is used for neutralizing wet process phosphoric acid.
Claim 6
Dependent Claim
20 words
The process of claim 1, wherein the alkali metal hydroxide used has a strength between 20 and 50 weight percent.
Claim 7
Dependent Claim
45 words
The process of claim 1, wherein phosphoric acid is added to establish an alkali metal oxide: P2O5-molar ratio between 2.5 and 3.5 and water or recycled wash solution is added to the resulting solution to establish a P2O5concentration between 7 and 9 weight percent therein.
Claim 8
Dependent Claim
26 words
The process of claim 4, wherein the solution is cooled down to 20* C. and the trialkali metal phosphate is then separated from the mother liquor.
Claim 9
Dependent Claim
40 words
The process of claim 6, wherein the trialkali metal phosphate is used in combination with at least one substance selected from the group consisting of alkali metal hydroxide and alkali metal carbonate for the neutralization of wet process phosphoric acid.