JP4036426B2

JP4036426B2 - Method for producing gypsum with excellent filterability

Info

Publication number: JP4036426B2
Application number: JP2001253274A
Authority: JP
Inventors: 尚和初治; 登初田; 庄三天野
Original assignee: Shimonoseki Mitsui Chemicals Inc
Current assignee: Shimonoseki Mitsui Chemicals Inc
Priority date: 2001-08-23
Filing date: 2001-08-23
Publication date: 2008-01-23
Anticipated expiration: 2021-08-23
Also published as: JP2003054944A

Description

【０００１】
【発明の属する技術分野】
本発明は、ニ水−半水法による湿式リン酸の製造の際、ろ過性の優れた石膏を製造する方法に関するものである。
【０００２】
【従来の技術】
ニ水−半水法による湿式リン酸の製造においては、リン酸収量の向上をはかり、且つ副生石膏を石膏ボ−ドやセメント用として有効利用することが必要となる。この為、石膏格子中に残存するリン酸分を低減、即ち、ろ過性の優れた石膏を製造することが必要となる。従来、ろ過性の優れた石膏の製造と、装置の腐食防止の観点から珪藻土等のシリカ質を添加していた（特開昭５７−１２９８１１、特開昭５２−２１２９６）。
【０００３】
ところが、リン鉱石によっては、珪素土等の添加では、石膏の良好なろ過性を維持できず、事実上、使用できないということがあった。しかし、リン鉱石ソースの枯渇が懸念される中、石膏の良好なろ過性の維持のみでなく、不純物量の低いリン酸や石膏を製造するには、従来法に代わる新しい製造方法、即ち、従来の方法、装置では使用できなかったリン鉱石の使用技術の開発が望まれていた。
また、ニ水−半水法による湿式リン酸の製造において、珪藻土等の添加量は、以下に示す分析方法に基づいて予想されていた。
【０００４】
リン鉱石中にはリンやカルシウム分はもとより、フッ素やケイ素分が含有されている。更に、ケイ素分は、反応性の高い活性成分と反応性の低い不活性成分からなると考えられている。
リン鉱石中のフッ素とケイ素の活性成分はリン鉱石の分解時に下記反応式によりケイフッ化物になると考えられており、
６Ｆ^-＋Ｓｉ → ＳｉＦ₆ ^-
この反応で不足するケイ素の活性成分をシリカに換算し、珪藻土等として添加している。更に詳述すると、リン鉱石中のフッ素の分析方法としては、リン鉱石を過塩素酸中、１４０〜１４５℃で蒸留分解し、得られた蒸留液中のフッ素分をフッ素イオンメーターで分析する。リン鉱石中のケイ素分は、アルカリ溶融分を原子吸光法で分析し、この値をシリカに換算し、「トータルシリカ」とする。また、煮沸した王水へのリン鉱石の不溶分を「王水不溶分」とし、この「王水不溶分」を「トータルシリカ」から差し引いた値を（従来の）活性シリカと呼んでいる。
【０００５】
添加する珪藻土等のシリカ分は、煮沸した水酸化ナトリウムへの可溶分を重量法で求め有効シリカ分とする。従来の方法では、リン鉱石中のフッ素と（従来の）活性シリカのモル比、即ち、フッ素／（従来の）活性シリカが６になるよう珪藻土等の添加で調製していた。しかし、これらの分析値を利用して運転を行なった場合、分析値から予想される珪藻土等の添加量と実際の運転時の添加量が一致しないのが普通で、熟練した運転者が結晶形状を顕微鏡観察しながら調整しているのが実情であった。
また、リン鉱石によっては、これら分析値からの予想では（従来の）活性シリカが大幅に不足しているのにも関わらず、石膏の良好なろ過性を維持するためには、（従来の）活性シリカを補うための珪藻土等は全く添加できず、事実上、運転不可能ということがあった。
【０００６】
【発明が解決しようとする課題】
本発明は従来のニ水−半水法による湿式リン酸の製造方法の問題点、即ち、従来法では、使用不可能であったリン鉱石の使用、更には、珪藻土や本発明のフッ素系化合物の添加量の正確な予想等の課題を解決するものである。
【０００７】
【課題を解決するための手段】
かかる課題を解決すべく本発明者らは鋭意検討を行なった結果、本発明を完成するに至った。即ち、ニ水−半水法による湿式リン酸の製造方法において、フッ素系化合物、及び／または、半水石膏を添加することにより、従来の方法、装置では使用できなかったリン鉱石を用いて、ろ過性の優れた石膏を製造できる方法を提供するに至った。更には、本発明の分析方法、即ち、リン鉱石中の「トータルシリカ」から「王水不溶分中のシリカ」分を差し引いた値を「活性シリカ」とする方法を用いることにより、フッ素系化合物の添加量、更には、珪藻土等のシリカ質の添加量も正確に予想することができるようになった。
【０００８】
【発明の実施の形態】
本発明でいう「ニ水−半水法」とは、
（１）リン鉱石を硫酸で分解して、ニ水石膏を含むリン酸スラリーを得、
（２）上記リン酸スラリーを製品湿式リン酸と含リンニ水石膏とに分離し、
（３）上記含リンニ水石膏を、硫酸または、硫酸とリン酸との混酸と接触させ、石膏のニ水−半水転移点以上の温度に保持してニ水石膏を半水石膏に転移させ、
（４）（３）で得られたスラリーをろ過し、
（５）（４）で得られたろ液を（１）の工程へ循環する。
ことを主工程とする、湿式リン酸の製造方法である。
また、分解槽とは上記（１）の分解を行なわせる反応器を、改質槽とは上記（３）の転移を行なわせる反応器をいう。
実際の製造プロセスでは、生成した酸の循環利用や、排水処理で得られたケーキの再利用など、様々な改良が付加されている。本発明は、これら改良プロセスにも同様に適用することができる。
【０００９】
本発明のフッ素系化合物として、フッ素系化合物の製造原料として使用される高純度のフッ酸でも良いし、半導体工場等から排出される廃フッ酸でも良い。
また、合成フッ化カルシウムや螢石、フルオロアパタイト、フッ化アルミニウム、氷晶石等、酸の中でフッ素イオンを供給できるものなら何れの化合物でも良いが、化合物の安定性が高く、例えば、結晶性の高い天然蛍石等を使用する場合は、硫酸で予め分解してから添加することが望ましい。また、フッ素系化合物にナトリウムが含まれる場合には、イオン交換などで除去してから使用することが望ましい。ナトリウムが存在すると、石膏結晶の粒径が小さくなりやすくろ過性が悪化し、また、生成した石膏を建材用の石膏ボードとして用いる場合、たわみの原因ともなるからである。
【００１０】
本発明のフッ素系化合物の添加場所としては、最終的に改質層に流入するなら、いずれの場所に添加しても良い。フッ素系化合物がフッ酸等の揮発性の高い化合物の場合、改質槽に直接添加した方が好ましい。揮発性が高い場合、改質槽に到達する前に、添加したフッ素分の多くが飛散すると考えるからである。
フッ素系化合物の添加率としては、リン鉱石中の不足フッ素分を補うように添加することが望ましい。不足フッ素分とは、モル比で、フッ素／「活性シリカ」を５以上にすることが望ましい。実際の製造現場で石膏のろ過性を調整するためには、分解槽の硫酸濃度、温度、更には、リン酸の単位時間当たりの製造量等を調整するため、一概に、フッ素／「活性シリカ」の値を決めることは難しいが、フッ素／「活性シリカ」の値が大きいほど、石膏の結晶形状は大きくなり、ろ過性は向上することが分かっている。但し、フッ素／「活性シリカ」の値が、８を超えて著しく大きな値になると、ろ過性は向上するものの装置の腐食が懸念される。
【００１１】
リン鉱石中のフッ素の分析方法としては、リン鉱石を過塩素酸中、１４０〜１４５℃で蒸留分解し、得られた蒸留液中のフッ素分をフッ素イオンメーターで分析する。リン鉱石中のケイ素分は、アルカリ溶融分を原子吸光法で分析し、この値をシリカに換算し、「トータルシリカ」とする。ここまでは従来法と同じであるが、更に「王水不溶分」中のケイ素分を同様の方法で分析し、この値をシリカに換算し、「王水不溶分中のシリカ」とする。「王水不溶分」の分析に用いる王水は、通常、濃硝酸と濃塩酸の体積比１：３の混液であるが、この王水の代わりに改質槽と同様な組成を有する混酸、即ち、リン酸と硫酸の混液を使用しても同様の分析値が得られる。得られた分析値から、「トータルシリカ」−「王水不溶分中のシリカ」を「活性シリカ」とする。
添加する珪藻土等のシリカ分も、従来法と同じく、煮沸した水酸化ナトリウムへの可溶分を重量法で求め有効シリカ分とする。
【００１２】
本発明の半水石膏は、ニ水−半水法による湿式リン酸の製造により副生した半水石膏をを使用することができる。副生した半水石膏は、ろ過したものを使用しても良いし、沈降分離したものを用いても良い。半水石膏であれば、本発明に効果が得られるが、急激に乾燥して半水石膏の表面に無水石膏が生成したものは好ましくない。半水石膏の添加量としては、ドライベースで湿式リン酸の製造時に副生する石膏の５ｗｔ％以上であることが望ましい。半水石膏の添加方法としては、改質槽に連続的にフィードしても良いし、添加する量を分けて間欠的に投入しても良い。
【００１３】
【実施例】
以下、実施例により本発明を詳細に説明する。
本発明で用いたリン鉱石の分解スラリーは、リン鉱石、９８％硫酸、更に改質層スラリーのろ液を混合して表１の組成になるように調製したものを用いた。リン鉱石の分解は約７０℃で行った。
Ｐ₂Ｏ₅濃度は中和滴定法で、ＳＯ₃濃度は比濁法で分析した。また、スラリー濃度は、リン鉱石のスラリーをろ過後、ケーキとほぼ同量の温水で洗浄し、約４５℃で恒量になるまで乾燥した。最初のスラリー重量に対する乾燥後のケーキの重量をスラリー濃度とした。
【００１４】
【表１】

【００１５】
また、本発明を実施する際の改質槽には、表１のスラリーと９８％硫酸、必要によっては水をチューブポンプでフィードしながら、表２の組成になるように調製した。改質槽はフッ素系樹脂の容器を用い、オイルバスに浸漬してスラリー温度を約８５℃になるよう調整した。また、改質槽へのフィードは連続的に行い、改質槽の片方に設けた口からオーバーフローした石膏スラリーを採取した。採取した石膏スラリーを速やかにろ過し、ろ液は分取した後、ケーキをほぼ同量の温水で洗浄した。更に、石膏の水和を停止させるため、ケーキとほぼ同量のメタノールで洗浄後、４５℃で乾燥した。分取したろ液は、中和滴定法により、Ｐ₂Ｏ₅濃度とＨ₂ＳＯ₄濃度を測定し、表２の組成となっていることを確認した。
【００１６】
また、リン鉱石の分解スラリーと同様な方法でスラリー濃度も測定した。乾燥後の石膏のろ過性を示す指標としては、ブレーン値を用いた。ブレーン値は、粉体に対する空気の透過性を示す指標であり、石膏の場合、ブレーン値が低いほどろ過性が良くなることが分かっている。ブレーン値の測定は、島津粉体比表面積測定装置を用いた。
【００１７】
【表２】

【００１８】
リン鉱石は、南アフリカ共和国産のもの２種類を用いた。それぞれの組成を表３に示す。
【００１９】
【表３】

【００２０】
実施例１
２リットルの改質槽に、リン鉱石としてＰａｌｆｏｓＥを分解して調製した表１のスラリーと９８％硫酸をチューブポンプで送液した。更に、フッ素／活性シリカ＝５．６となるように５５％ＨＦをリン鉱石に対してＦとして１．３％添加した。改質槽のろ液組成が表２の組成に入るように調整しながら１２時間連続運転を行ない、得られた石膏のブレーン値を代表値とした。結果を表４に示す。石膏のブレーン値は、１１３０ｃｍ²／ｇであり、ろ過性の優れた石膏が得られた。
【００２１】
実施例２〜４
添加剤の種類と添加率を表４に示したように変えた以外は、実施例１と同様の操作を行なった。結果を表４に示す。ブレーン値の測定結果を表４に示す。いずれもろ過性の優れた石膏が得られた。
【００２２】
実施例５〜６
添加剤として本実施例で生成した半水石膏を、半水石膏添加前に発生していた石膏に対して２０％、連続的に添加した以外は、実施例１と同様の操作を行った。結果を表４に示す。ブレーン値の測定結果を表４に示す。いずれもろ過性の優れた石膏が得られた。
【００２３】
実施例７
添加剤として半水石膏と５５％ＨＦの両方を表４に示した添加率で添加した以外は、実施例１と同様の操作を行った。結果を表４に示す。石膏のブレーン値は、１０１０ｃｍ²／ｇであり、ろ過性の優れた石膏が得られた。
【００２４】
比較例１
添加剤の添加を中止し、実施例１と同様の操作を行なった。従来の分析方法によれば、表４に示したように、フッ素／（従来の）活性シリカ＝１３．５とフッ素が過剰であり、ろ過性の良好な石膏が得られることが予想される。しかし、得られた石膏のブレーン値は、２８００ｃｍ²／ｇであり、ろ過性の非常に悪い石膏が得られた。現実の製造設備では、リン酸の収率、石膏の水和等を考慮すると運転不可能となる。結果を表４に示す。
【００２５】
比較例２
添加剤として珪藻土を添加し実施例１と同様の操作を行なった。従来の分析方法によれば、表４に示したように、フッ素／（従来の）活性シリカ＝６．３となり、ろ過性の良好な石膏が得られることが予想される。しかし、得られた石膏のブレーン値は、６２００ｃｍ²／ｇであり、ろ過性の非常に悪い石膏が得られた。現実の製造設備では、リン酸の収率、石膏の水和等を考慮すると運転不可能となる。結果を表４に示す。
使用した珪藻土は、中国吉林省産で、有効シリカ分は、７６．５％だった。
【００２６】
比較例３
添加剤としてニ水石膏をを表４の添加率で添加した以外は、実施例１と同様の操作を行なった。結果を表４に示す。
得られた石膏のブレーン値は、２６３０ｃｍ²／ｇであり、ろ過性の非常に悪い石膏が得られた。現実の製造設備では、リン酸の収率、石膏の水和等を考慮すると運転不可能となる。
【００２７】
【表４】

【００２８】
更に、従来から使用されているリン鉱石であるＰａｌｆｏｓ８８Ｓを使用し、珪藻土を添加した場合の実施例を示す。珪藻土は、比較例２で使用したものを用いた。
【００２９】
実施例８
リン鉱石としてＰａｌｆｏｓ８８Ｓを分解して調製した表１のスラリーを用い、添加剤として珪藻土を用いた以外は、実施例１と同様の操作を行った。珪藻土の添加量としては、フッ素／活性シリカのモル比が、６．０になるよう調整した。このとき、フッ素／（従来の）活性シリカのモル比は、１９．５だった。結果を表５に示す。
得られた石膏のブレーン値は、１０２０ｃｍ²／ｇであり、ろ過性の優れた石膏が得られた。
【００３０】
比較例４
珪藻土の添加量としては、フッ素／（従来の）活性シリカのモル比が、５．９になるよう調整した以外は、実施例８と同様の操作を行った。このとき、フッ素／活性シリカのモル比は、３．５だった。結果を表５に示す。
得られた石膏のブレーン値は、２３００ｃｍ²／ｇであり、ろ過性の非常に悪い石膏が得られた。
従来の分析方法で予想した珪藻土添加量では、優れたろ過性の石膏を得ることができない。
【００３１】
【表５】

【００３２】
【発明の効果】
以上説明したように、本発明のフッ素化合物、及び／または、半水石膏を添加することにより、従来の方法、装置では使用できなかったリン鉱石を用いて、ろ過性の優れた石膏を製造できるようになった。
更には、本発明の分析方法、即ち、リン鉱石中の「トータルシリカ」から「王水不溶分中のシリカ」分を差し引いた値を「活性シリカ」とする方法を用いることにより、フッ素系化合物の添加量（シリカ分が不足な場合には珪藻土等のシリカ質の添加量）を正確に予想することができるようになった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing gypsum having excellent filterability in the production of wet phosphoric acid by a diwater-half-water method.
[0002]
[Prior art]
In the production of wet phosphoric acid by the two-water-half-water method, it is necessary to improve the phosphoric acid yield and to effectively use the by-product gypsum for gypsum board and cement. For this reason, it is necessary to reduce the phosphoric acid content remaining in the gypsum lattice, that is, to produce gypsum with excellent filterability. Conventionally, siliceous materials such as diatomaceous earth have been added from the viewpoint of producing gypsum with excellent filterability and preventing corrosion of the apparatus (Japanese Patent Laid-Open Nos. 57-1229811 and 52-21296).
[0003]
However, depending on the phosphorus ore, the addition of silicon earth or the like cannot maintain the good filterability of gypsum, and in fact, cannot be used. However, while there is concern about the depletion of the phosphate ore source, not only maintaining good filterability of gypsum, but also producing phosphoric acid and gypsum with low impurities, a new production method that replaces the conventional method, Development of a technique for using phosphorus ore that could not be used with this method and apparatus has been desired.
In addition, in the production of wet phosphoric acid by the two-water-half-water method, the addition amount of diatomaceous earth and the like has been predicted based on the analysis method shown below.
[0004]
The phosphorus ore contains not only phosphorus and calcium but also fluorine and silicon. Furthermore, the silicon content is considered to consist of a highly reactive active ingredient and a less reactive inactive ingredient.
The active component of fluorine and silicon in the phosphate ore is considered to be silicofluoride by the following reaction formula when the phosphate ore is decomposed,
6F ^{^-} + Si → SiF ₆ ^-
The active component of silicon deficient in this reaction is converted to silica and added as diatomaceous earth. More specifically, as a method for analyzing fluorine in phosphate ore, phosphate ore is distilled and decomposed at 140 to 145 ° C. in perchloric acid, and the fluorine content in the obtained distillate is analyzed with a fluorine ion meter. As for the silicon content in the phosphate ore, the alkali melt is analyzed by atomic absorption, and this value is converted to silica to obtain “total silica”. Also, the insoluble content of the phosphate ore in the boiled aqua regia is called “aqua regia insoluble”, and the value obtained by subtracting this “aqua regia insoluble” from the “total silica” is called (conventional) activated silica.
[0005]
The silica content such as diatomaceous earth to be added is determined by the weight method for the soluble content in boiled sodium hydroxide and is defined as the effective silica content. In the conventional method, the molar ratio of fluorine in the phosphate ore to (conventional) active silica, that is, fluorine / (conventional) active silica is adjusted to 6 by adding diatomaceous earth or the like. However, when operation is performed using these analytical values, the amount of diatomaceous earth, etc. predicted from the analytical values usually does not match the actual amount of operation, and a skilled driver has a crystal shape. It was the actual situation that was adjusted while observing the microscope.
In addition, depending on the phosphate ore, in order to maintain the good filterability of gypsum (conventional) despite the large lack of active silica (conventional) as expected from these analytical values, Diatomaceous earth or the like for supplementing the active silica could not be added at all, and it was practically impossible to operate.
[0006]
[Problems to be solved by the invention]
The present invention is a problem of a conventional method for producing wet phosphoric acid by a diwater-semi-water method, that is, the use of phosphorus ore that could not be used in the conventional method, diatomaceous earth, and the fluorine-based compound of the present invention. It solves problems such as accurate prediction of the amount of addition.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, in the method for producing wet phosphoric acid by the diwater-half-water method, by adding a fluorine-based compound and / or hemihydrate gypsum, using the phosphate ore that could not be used in the conventional method, apparatus, It came to provide the method which can manufacture the gypsum excellent in filterability. Furthermore, by using the analysis method of the present invention, that is, a method in which the value obtained by subtracting the “silica in aqua regia insolubles” from “total silica” in the phosphate ore is “active silica”, the fluorine compound In addition, the amount of siliceous material such as diatomaceous earth can be accurately predicted.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the “ni water-half water method”
(1) Decomposing phosphorus ore with sulfuric acid to obtain a phosphoric acid slurry containing dihydrate gypsum,
(2) The phosphoric acid slurry is separated into product wet phosphoric acid and phosphorous dihydrate gypsum,
(3) The phosphorous dihydrate gypsum is brought into contact with sulfuric acid or a mixed acid of sulfuric acid and phosphoric acid, and the dihydrate gypsum is transferred to the hemihydrate gypsum by maintaining the temperature above the diwater-halfwater transition point of the gypsum. ,
(4) Filter the slurry obtained in (3),
(5) The filtrate obtained in (4) is circulated to the step (1).
This is a method for producing wet phosphoric acid.
Further, the decomposition tank refers to a reactor that performs the decomposition of (1) above, and the reformer tank refers to a reactor that performs the transfer of (3) above.
In the actual manufacturing process, various improvements such as recycling of the generated acid and recycling of the cake obtained by the wastewater treatment are added. The present invention is equally applicable to these improved processes.
[0009]
The fluorine-based compound of the present invention may be high-purity hydrofluoric acid used as a raw material for producing the fluorine-based compound, or waste hydrofluoric acid discharged from a semiconductor factory or the like.
In addition, any compound can be used as long as it can supply fluorine ions in the acid, such as synthetic calcium fluoride, meteorite, fluoroapatite, aluminum fluoride, cryolite, etc., but the stability of the compound is high. When natural fluorite or the like having high properties is used, it is desirable to add it after decomposing in advance with sulfuric acid. Moreover, when sodium is contained in a fluorine-type compound, it is desirable to use, after removing by ion exchange etc. If sodium is present, the particle size of the gypsum crystals tends to be small, and the filterability is deteriorated. Also, when the generated gypsum is used as a gypsum board for building materials, it may cause deflection.
[0010]
As a place where the fluorine-based compound of the present invention is added, it may be added to any place as long as it finally flows into the modified layer. When the fluorine compound is a highly volatile compound such as hydrofluoric acid, it is preferable to add it directly to the reforming tank. This is because when the volatility is high, it is considered that much of the added fluorine is scattered before reaching the reforming tank.
As the addition rate of the fluorine-based compound, it is desirable to add so as to compensate for the insufficient fluorine content in the phosphate ore. The insufficient fluorine content is preferably a molar ratio of fluorine / “active silica” of 5 or more. In order to adjust the filterability of gypsum at the actual production site, in order to adjust the sulfuric acid concentration and temperature of the decomposition tank, and also the production amount of phosphoric acid per unit time, generally, fluorine / “active silica However, it is known that the larger the fluorine / “active silica” value, the larger the crystal shape of gypsum and the better the filterability. However, when the value of fluorine / “active silica” exceeds 8 and becomes a remarkably large value, the filterability is improved, but the apparatus may be corroded.
[0011]
As a method for analyzing the fluorine in the phosphate ore, the phosphate ore is distilled and decomposed in perchloric acid at 140 to 145 ° C., and the fluorine content in the obtained distillate is analyzed with a fluorine ion meter. As for the silicon content in the phosphate ore, the alkali melt is analyzed by atomic absorption, and this value is converted to silica to obtain “total silica”. The process so far is the same as the conventional method, but the silicon content in the “aqua regia insoluble matter” is further analyzed by the same method, and this value is converted to silica to obtain “silica in the aqua regia insoluble content”. The aqua regia used for the analysis of “aqua regia insoluble” is usually a mixture of concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1: 3, but instead of this aqua regia, a mixed acid having the same composition as the reforming tank, That is, the same analytical value can be obtained even if a mixed solution of phosphoric acid and sulfuric acid is used. From the analytical values obtained, “total silica” − “silica in aqua regia insolubles” is defined as “active silica”.
As for the silica content such as diatomaceous earth to be added, the soluble content in boiled sodium hydroxide is obtained by the gravimetric method and used as the effective silica content as in the conventional method.
[0012]
As the hemihydrate gypsum of the present invention, hemihydrate gypsum by-produced by the production of wet phosphoric acid by the diwater-half water method can be used. The by-product hemihydrate gypsum may be filtered or may be precipitated and separated. If it is hemihydrate gypsum, the effect of the present invention can be obtained, but it is not preferred that it is dried rapidly and anhydrous gypsum is formed on the surface of hemihydrate gypsum. The amount of hemihydrate gypsum added is desirably 5 wt% or more of gypsum by-produced during the production of wet phosphoric acid on a dry basis. As a method for adding hemihydrate gypsum, it may be continuously fed to the reforming tank or may be added intermittently by dividing the amount to be added.
[0013]
【Example】
Hereinafter, the present invention will be described in detail by way of examples.
The decomposition slurry of the phosphate ore used in the present invention was prepared by mixing the phosphate ore, 98% sulfuric acid and the filtrate of the modified layer slurry so as to have the composition shown in Table 1. The decomposition of the phosphate ore was performed at about 70 ° C.
The P ₂ O ₅ concentration was analyzed by neutralization titration, and the SO ₃ concentration was analyzed by turbidimetry. In addition, the slurry concentration was obtained by filtering the phosphorus ore slurry, washing with approximately the same amount of hot water as the cake, and drying at about 45 ° C. until a constant weight was obtained. The weight of the cake after drying relative to the initial slurry weight was taken as the slurry concentration.
[0014]
[Table 1]

[0015]
In addition, the reforming tank for carrying out the present invention was prepared so as to have the composition shown in Table 2 while feeding the slurry of Table 1 and 98% sulfuric acid and, if necessary, water with a tube pump. As the reformer, a fluorine resin container was used, and the slurry temperature was adjusted to about 85 ° C. by immersion in an oil bath. Moreover, the feed to the reforming tank was continuously performed, and the gypsum slurry overflowed from the mouth provided on one side of the reforming tank was collected. The collected gypsum slurry was quickly filtered, and the filtrate was collected, and then the cake was washed with approximately the same amount of hot water. Furthermore, in order to stop the hydration of gypsum, it was washed with approximately the same amount of methanol as the cake and then dried at 45 ° C. The collected filtrate was measured for P ₂ O ₅ concentration and H ₂ SO ₄ concentration by a neutralization titration method, and it was confirmed that the composition shown in Table 2 was obtained.
[0016]
The slurry concentration was also measured by the same method as the decomposition slurry of phosphorus ore. The brain value was used as an index indicating the filterability of gypsum after drying. The brane value is an index indicating the permeability of air to the powder. In the case of gypsum, it is known that the lower the brane value, the better the filterability. The brane value was measured using a Shimadzu powder specific surface area measuring device.
[0017]
[Table 2]

[0018]
Two types of ore from South Africa were used. The respective compositions are shown in Table 3.
[0019]
[Table 3]

[0020]
Example 1
The slurry of Table 1 and 98% sulfuric acid prepared by decomposing Parfos E as a phosphate ore and 98% sulfuric acid were sent to a 2 liter reformer by a tube pump. Furthermore, 1.3% of 55% HF was added as F to the phosphate ore so that fluorine / active silica = 5.6. A continuous operation was carried out for 12 hours while adjusting the filtrate composition of the reforming tank to fall within the composition shown in Table 2, and the brain value of the obtained gypsum was used as a representative value. The results are shown in Table 4. The bran value of gypsum was 1130 cm ² / g, and gypsum with excellent filterability was obtained.
[0021]
Examples 2-4
The same operation as in Example 1 was performed except that the type and addition rate of the additive were changed as shown in Table 4. The results are shown in Table 4. Table 4 shows the measurement results of the brane value. In all cases, gypsum with excellent filterability was obtained.
[0022]
Examples 5-6
The same operation as in Example 1 was performed except that 20% of the hemihydrate gypsum produced in this example was continuously added as an additive to the gypsum generated before the addition of hemihydrate gypsum. The results are shown in Table 4. Table 4 shows the measurement results of the brane value. In all cases, gypsum with excellent filterability was obtained.
[0023]
Example 7
The same operation as in Example 1 was performed except that both hemihydrate gypsum and 55% HF were added as additives as shown in Table 4. The results are shown in Table 4. The brane value of gypsum was 1010 cm ² / g, and gypsum with excellent filterability was obtained.
[0024]
Comparative Example 1
Addition of the additive was stopped, and the same operation as in Example 1 was performed. According to the conventional analysis method, as shown in Table 4, fluorine / (conventional) active silica = 13.5 and fluorine are excessive, and it is expected that gypsum with good filterability can be obtained. However, the obtained plaster had a brain value of 2800 cm ² / g, and a plaster with very poor filterability was obtained. In an actual production facility, operation becomes impossible in consideration of the yield of phosphoric acid, the hydration of gypsum, and the like. The results are shown in Table 4.
[0025]
Comparative Example 2
Diatomaceous earth was added as an additive and the same operation as in Example 1 was performed. According to the conventional analysis method, as shown in Table 4, fluorine / (conventional) active silica = 6.3, and it is expected that gypsum with good filterability can be obtained. However, the obtained plaster had a brain value of 6200 cm ² / g, and a plaster with very poor filterability was obtained. In an actual production facility, operation becomes impossible in consideration of the yield of phosphoric acid, the hydration of gypsum, and the like. The results are shown in Table 4.
The diatomite used was from Jilin Province, China, and the effective silica content was 76.5%.
[0026]
Comparative Example 3
The same operation as in Example 1 was performed except that dihydrate gypsum was added as an additive at the addition rate shown in Table 4. The results are shown in Table 4.
The obtained plaster had a brain value of 2630 cm ² / g, and a plaster with very poor filterability was obtained. In an actual production facility, operation becomes impossible in consideration of the yield of phosphoric acid, the hydration of gypsum, and the like.
[0027]
[Table 4]

[0028]
Furthermore, the Example at the time of using diatomaceous earth using Palfos 88S which is the phosphorus ore conventionally used is shown. The diatomaceous earth used in Comparative Example 2 was used.
[0029]
Example 8
The same operation as in Example 1 was performed, except that the slurry shown in Table 1 prepared by decomposing Palmos 88S as the phosphorus ore was used and diatomaceous earth was used as the additive. The addition amount of diatomaceous earth was adjusted so that the molar ratio of fluorine / active silica was 6.0. At this time, the molar ratio of fluorine / (conventional) activated silica was 19.5. The results are shown in Table 5.
The obtained plaster had a brain value of 1020 cm ² / g, and a plaster excellent in filterability was obtained.
[0030]
Comparative Example 4
As the addition amount of diatomaceous earth, the same operation as in Example 8 was performed except that the molar ratio of fluorine / (conventional) active silica was adjusted to 5.9. At this time, the molar ratio of fluorine / active silica was 3.5. The results are shown in Table 5.
The obtained plaster had a brain value of 2300 cm ² / g, and a plaster with very poor filterability was obtained.
With the amount of diatomaceous earth predicted by the conventional analysis method, an excellent filterable gypsum cannot be obtained.
[0031]
[Table 5]

[0032]
【The invention's effect】
As described above, by adding the fluorine compound and / or hemihydrate gypsum of the present invention, gypsum with excellent filterability can be produced using phosphorus ore that could not be used in conventional methods and apparatuses. It became so.
Furthermore, by using the analysis method of the present invention, that is, a method in which the value obtained by subtracting the “silica in aqua regia insolubles” from “total silica” in the phosphate ore is “active silica”, the fluorine compound (The amount of siliceous material such as diatomaceous earth when the silica content is insufficient) can be accurately predicted.

Claims

(1) In a decomposition tank, phosphorous ore is decomposed with sulfuric acid to obtain a phosphoric acid slurry containing dihydrate gypsum, (2) the phosphoric acid slurry is separated into product wet phosphoric acid and phosphorous dihydrate gypsum, 3) In the reformer tank, the above-mentioned phosphorus-containing dihydrate gypsum is brought into contact with sulfuric acid or a mixed acid of sulfuric acid and phosphoric acid, and maintained at a temperature equal to or higher than the diwater-half-water transition point of gypsum. Transfer to gypsum, filter the slurry obtained in (4) and (3), and circulate the filtrate obtained in (5) and (4) to the step (1). In the manufacturing method of wet phosphoric acid by the water method , the silicon content in the phosphate ore is alkali-melted and analyzed by atomic absorption method to convert it to silica to make “total silica”. In the same way, the silicon content in the insoluble matter is analyzed and converted to silica. The value obtained by subtracting the “silica in the aqua regia insolubles” from the “total silica” in the phosphate ore is referred to as “active silica”, and the molar ratio of fluorine in the phosphate ore to the active silica ( = fluorine / active silica) are formed so that 5 or more, the fluorine-based compound, a method for producing a filtration excellent in plaster which comprises adding to the reforming chamber.

(1) In a decomposition tank, phosphorous ore is decomposed with sulfuric acid to obtain a phosphoric acid slurry containing dihydrate gypsum, (2) the phosphoric acid slurry is separated into product wet phosphoric acid and phosphorous dihydrate gypsum, 3) In the reformer tank, the above-mentioned phosphorus-containing dihydrate gypsum is brought into contact with sulfuric acid or a mixed acid of sulfuric acid and phosphoric acid, and maintained at a temperature equal to or higher than the diwater-half-water transition point of gypsum. Transfer to gypsum, filter the slurry obtained in (4) and (3), and circulate the filtrate obtained in (5) and (4) to the step (1). In the method for producing wet phosphoric acid by the water method, to the modification tank for transferring the dihydrate gypsum to hemihydrate gypsum, hemihydrate gypsum is added continuously or intermittently, and the addition amount of the hemihydrate gypsum is: the filterability of the superior gypsum, characterized in that the reforming is newly generated by the vessel at least 5% of the hemihydrate gypsum How to elephants.

The addition of the fluorine-based compound to the reforming tank according to claim 1 and the addition of hemihydrate gypsum to the reforming tank according to claim 2 are simultaneously produced. How to do .