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US4101638A Expired / Lapsed US ⏱️ 0.0 years remaining

Process for the manufacture of a slurry containing highly concentrated phosphoric acid and calcium sulfate hemihydrate in a readily filterable form

Assignee: Nissan Chemical Corp
•
Filing: 1976-08-02
•
Granted: 1978-07-18
•
Expires: 1996-08-02
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Abstract

Abstract The present invention relates to a wet process for the manufacture of phosphoric acid, which process essentially comprises a digestion step in which phosphate rock is digested by means of phosphoric acid and sulfuric acid to form a slurry containing highly concentrated phosphoric acid together with calcium sulfate hemihydrate, and a separation step in which the slurry is filtered for separation of calcium sulfate hemihydrate from the highly concentrated phosphoric acid (in which the concentration of P205 in the product acid is higher than 40% by weight, based on the weight of the product acid) and which is characterized by supplying active silica at a ratio of 0.2-5% by weight, based on the weight of phosphate rock, in order that active silica may be present in the above mentioned digestion step.

Inventors

  • 👤 Takasuke Inoue
  • 👤 Yuzo Itoh
  • 👤 Sataro Nakajima
  • 👤 Shin-Ichi Tajika
  • 👤 Yoshio Saiki

Bibliographic Details

Application Number —
Jurisdiction US
Data Source google_patents
Last Synchronized 2026-11-04 05:45
CPC Classifications
C; C01; C01B; C01B25/00; C01B25/16; C01B25/18; C01B25/22

Claims Analysis

Total Claims: 7
Claim 1
Independent Claim 89 words
In a wet process for the manufacture of highly concentrated phosphoric acid, which process comprises a digestion step in which phosphate rock is digested by phosphoric acid and sulphuric acid to produce a slurry containing phosphoric acid having a P 2 O 5 concentration in excess of 40%, together with calcium sulfate hemihydrate and a separation step in which the slurry is filtered to separate said calcium sulfate hemihydrate from said highly concentrated phosphoric acid, the improvement which comprises the step of introducing active silica during the digestion step.
Claim 2
Dependent Claim 89 words
In a wet process for the manufacture of highly concentrated phosphoric acid, which process comprises a digestion step in which phosphate rock is digested by phosphoric acid and sulphuric acid to produce a slurry containing phosphoric acid having a P 2 O 5 concentration in excess of 40%, together with calcium sulfate hemihydrate and a separation step in which the slurry is filtered to separate said calcium sulfate hemihydrate from said highly concentrated phosphoric acid, the improvement which comprises the step of introducing active silica during the digestion step.
Claim 3
Dependent Claim 19 words
Process according to claim 1, wherein a silica which reacts readily with hydrogen fluoride is used as active silica.
Claim 4
Dependent Claim 22 words
Process according to claim 1, in which said active silica is introduced as a component of a diatomaceous earth or silica gel.
Claim 5
Dependent Claim 19 words
Process according to claim 1, wherein active silica exists in the digestion step in a 0.5-2% by weight amount.
Claim 6
Dependent Claim 75 words
Process according to claim 1, which further comprises a hydration step in which the separated calcium sulfate hemihydrate is converted into dihydrate by reaction with a mixture of diluted phosphoric acid and sulfuric acid, the filtrate obtained upon filtration to separate said dihydrate is circulated as a washing liquid for said hemihydrate, and a part of the phosphoric acid obtained upon filtration of said calcium sulfate hemihydrate is recycled and reused as the digesting acid.
Claim 7
Dependent Claim 14 words
Process according to claim 5, wherein active silica is added during the hydration step.

References Cited (Backward Citations)

US1969449A Cited
US3505013A Cited
US3653826A Cited
GB1248037A Cited
GB1278247A Cited

USPTO Annuity & Maintenance Windows

Annuity Stage Window Opens Payment Deadline Surcharge Period Until Estimated Fee Status
3.5 Years (Year 4) 1981-07-17 1982-01-16 1982-07-18 $2000.00 Window Closed / Lapsed
7.5 Years (Year 8) 1985-07-17 1986-01-16 1986-07-18 $3760.00 Window Closed / Lapsed
11.5 Years (Year 12) 1989-07-17 1990-01-16 1990-07-18 $7700.00 Window Closed / Lapsed

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