JP3927706B2

JP3927706B2 - Method and apparatus for electrolytic purification of gallium

Info

Publication number: JP3927706B2
Application number: JP31033298A
Authority: JP
Inventors: 健一田山; 長康梁田; 喜志雄田山
Original assignee: Dowa Holdings Co Ltd; Dowa Mining Co Ltd
Current assignee: Dowa Holdings Co Ltd
Priority date: 1998-10-30
Filing date: 1998-10-30
Publication date: 2007-06-13
Anticipated expiration: 2018-10-30
Also published as: JP2000144474A

Description

【０００１】
【発明の属する技術分野】
本発明はガリウムの電解精製法および装置に関する。
【０００２】
【従来の技術】
ガリウム金属は，ＧａＡｓやＧａＰ等の化合物半導体素子や発光素子の原料として，近来その需要が増大している。ガリウムは主としてアルミナ製造工程や亜鉛製錬の副産物として産出するが，その他，半導体材料のスクラップもガリウム原料となる。
【０００３】
このようなガリウム原料からのガリウム精製法には，従来より結晶精製法，単結晶引上げ法および電解精製法が良く知られている。
【０００４】
結晶精製法は，溶融したガリウム金属の冷却媒体側に種子結晶を存在せしめて冷却媒体による冷却効果で種子結晶を成長させ，成長した結晶側に精製された固体ガリウムを得る方法である。例えば特開平２−５０９２６号公報にはこのような結晶成長を多段で行う結晶精製法を開示している。
【０００５】
単結晶引上げ法は，溶融したガリウム金属中に種子結晶の先端を接触させ，この種子結晶から成長する，不純分の除かれた単結晶をゆっくり引上げる精製法である。例えば特開平２−２４３７２７号公報には，この方法において，溶融ガリウム表面に酸性溶液層を形成すると精製効率が向上すると教示している。
【０００６】
電解精製法は，ガリウム原料を陽極として通電すると電解液中にガリウムおよび電気化学的にガリウムより卑な金属が溶出し，陰極においてガリウムおよびガリウムより貴な金属が電着する性質を利用して，陰極に精製されたガリウム金属を得る方法である。例えば特開平６−１９２８７７号公報には，電解槽の底部にガリウム原料液体を入れ，この原料液体を陽極として棒状の陰極との間で電解を行うと，陰極表面に析出したガリウム金属は粒状となって滴下して下方の受器に捕集され，他方，ガリウム原料中のインジウム，銅，鉛などの不純物は陽極側に残されると教示している。
【０００７】
【発明が解決しようとする課題】
結晶精製法では，繰り返し操作しないとガリウム純度が上がらず，また工程が複雑で生産性が良くないこと等から，処理対象の原料としては５Ｎ以上（９９.９９９％以上）のガリウム金属を適用し，これを６Ｎ或いは７Ｎ以上（９９.９９９９％或いは９９.９９９９９９％以上）まで精製する高純度の領域での適用に限られることが多く，２Ｎ，３Ｎ程度の純度の原料については収率が悪く適さない。また，単結晶引上げ法についても同様に高純度の領域での適用に限られ，さらに設備が高価であるという問題がある。
【０００８】
一方，電解精製法は前２法に比べて工程は簡単で，ほとんど人手による操作を必要とせず，装置も安価であることから，高純度精製へのつなぎとしての，低純度精製法としても適用可能であるという利点がある。しかし，従来の電解精製法はインジウム，銅，鉛等を陽極中に濃縮して残すというものであり，所定量以上の不純物が陽極に濃縮すると，電解液中に不純物が入り込み，陰極に析出するガリウム純度が低下する結果となる。従って精製ガリウムの純度を規制した場合，自ずと電解寿命が決められることになる。また，従来の電解精製法では半導体スクラップ等に混入している「金」の除去ができないという問題がある。
【０００９】
【発明が解決しようとする課題】
したがって本発明は，安価で工程が単純であり，ほとんど人手による操作を必要としないガリウムの電解精製法において，従来法では除去できなかった金等の不純物を除去可能とし，かつ陽極中への不純物の濃縮度を上昇させ，しかも電解寿命を延ばすことができるガリウムの電解精製法を開発し，高収率でガリウムを精製することを課題としたものである。
【００１０】
【課題を解決するための手段】
本発明によれば，ガリウム原料液体を陽極として陰極に精製ガリウムを電解液中で析出させるガリウムの電解精製法において，該陽極表面に生成するスカムを電解槽の外に排出する操作と，電解終了までの間に陽極のガリウム原料液体を補給する操作を行うこと，更には電解液中のガリウム濃度を電解中所定範囲に維持する操作を行うことを特徴とするガリウムの電解精製法を提供する。
【００１１】
また，本発明によれば，ガリウム原料液体を陽極として収容する陽極室と，陰極に析出した精製ガリウムを捕集する陰極室とを有し，該陽極室と陰極室との間を通流するように電解液を入れたガリウム電解装置において，該陽極室を円筒状容器に構成し，この円筒状容器の外側下方に磁石回転子を設置すると共に該円筒状容器内の中心部にサクションパイプを配置し，また該電解装置の槽外に不溶性陽極と陰極をもつ補助電解槽を設けると共に該電解装置と補助電解槽の間を該電解液が循環する回路を設け，該循環回路にさらに中間槽を設置し，前記のサクションパイプをこの中間槽に連結し，この中間槽から電解装置に通ずる管路にフイルタを介装させたことを特徴とするガリウム電解精製装置を提供する。
【００１２】
【発明の実施の形態】
本発明者等は前記の課題を解決すべく鋭意試験研究を重ねた結果，不純物を含む溶融ガリウム金属（ガリウム原料液体と言う）を陽極とし，陰極に純度の高い精製ガリウム金属を析出させる電解精製法において，陽極表面に生成するスカムを電解液の一部と共に電解槽の外に排出する操作を行うと陽極残中の不純物濃度が高くなっても電解を続行させることができること，したがって，電解寿命を著しく改善できることを見い出した。またこのスカムを排出する操作を行うことにより，ガリウム原料中に同伴する金の除去が行えることがわかった。そして，陽極中の不純物濃度が高濃度でも電解を続行させることができることから，陽極のガリウム原料液体を補給しながら電解を行うことが可能となり，高い収率で精製ガリウムを得ることができる。そのさい，電解液中のガリウム濃度を一定にする操作を行うと，一層，電解寿命を長くすることができる。
【００１３】
電解液中のガリウム原料液体を回転（旋回）させると，回転中心の液表面に黒色を呈する物質が集まってくる。この物質は黒色を呈することからガリウム酸化物を含むものと見てよい。遠心分離を利用して陽極の回転中心にスカムを集め，このスカムをサクションパイプで吸い出せば，ガリウム原料液体と電解液との界面に発生する酸化膜の除去が容易に行えるし，金も除去できる点で，特別の効果をもたらす。該酸化膜の生成は電解効率を極端に悪くするし，金は通常のガリウム電解精製法では分離できないからである。
【００１４】
本発明者らは，この回転中心のガリウム原料液体表面に集まるスカムをサクションパイプを用いて吸い出す操作を行ったところ，驚くべきことに，金が同伴して吸い出されることを知った。その理由については必ずしも明らかではないが，電解の進行につれて原料液体の表面には主としてガリウムの酸化物が生成し，この酸化物が，原料ガリウムの液相よりも金を取込み易い性質を有しているのではないかと考えられる。
【００１５】
ガリウム原料液体に同伴する金は，通常の電解では，後記の比較例に示すように，陽極残（アノードスライム）には残存してこない。標準電極電位からすると金は最も貴な分類に入り，電気化学的にはガリウムの電解電位では陽極から液中に溶け出すことはない（イオン化しない）筈である。にも拘わらず陽極残に残らないのであるから，何らかの原因で電解液中にコロイド状となって分散してゆくのではないかと考えられる。そして，このコロイド状態で電解液中に浮遊する金の微粒子が，陰極においてガリウムイオンが電着するときに巻き込まれ，精製ガリウム中に同伴するようになると思われる。
【００１６】
このように，ガリウム原料に同伴する金は電解精製では除去し難いものであったが，本発明によると，サクションパイプを通じてスカムと共に金を同伴して抜き出すことができ，金の除去が非常に容易となった。他の不純物，例えばＩｎ，Ｃｕ，Ｐｂ等は金とは別の挙動を示し，陽極残として濃縮されてくる。
【００１７】
また，陽極表面からスカムを除去することにより，ガリウム原料中の不純物が陽極残に高濃度に濃縮されても電解を続行することができるようになり，また電解の途中で新たにガリウム原料液体を補給しても，支障なく電解を続行できる。そのさい，電解液中のガリウム濃度があまり高くなると陽極中の不純物も電解液中に溶けだすので，電解液中のガリウム濃度は１５０ｇ／Ｌ以下，好ましくは１００ｇ／Ｌ以下，さらに好ましくは６０ｇ／Ｌ以下に維持するのがよい。このため，電解槽の槽外に設置した電解採取槽に電解液を循環させ，この電解採取槽の陰極に電解液中のガリウムを析出させることによって，電解液中に過剰に溶存したガリウムを電解採取するのが望ましい。
【００１８】
しかし，電解液中のガリウム濃度があまり低くなると電流効率（電着金属量／理論電着金属量）が低くなるので電解液中のガリウム濃度は３０ｇ／Ｌ以上，好ましくは５０ｇ／Ｌ以上に維持するのが望ましい。該濃度が３０ｇ／Ｌ未満では電流効率は８０％を切るようになる。したがって，電解液中のガリウム濃度は３０〜１５０ｇ／Ｌ，好ましくは３０〜１００ｇ／Ｌ，さらに好ましくは５０〜６０ｇ／Ｌに維持するのがよい。
【００１９】
以下，本発明の実施の形態を図面を参照しながら説明する。図１は本発明法を実施する装置の例を示す略断面図であり，図２は該装置の電解槽の略平面を示したものである。
【００２０】
この装置は，電解液１を入れた電解槽２内を，ガリウム原料液体３を陽極としてこれを収容する陽極室４と，陰極に析出した精製ガリウムを捕集する陰極室５に区分し，陽極室４を円筒状容器６で形成し，この円筒状容器６の外側下方に磁石回転子７を設置し，円筒状容器６内の中心部にサクションパイプ８を配置したものである。円筒状容器６は内壁が真円であるのが理想的であるが，場合によっては部分的に角をもつ多角形であってもよく，また上下方向で半径が異なる内面をもつものであってもよい。９は絶縁被覆された導電ロッドである。この導電ロッド９の先端に取り付けた金属端子１０がガリウム原料液体３内に浸漬され，導電ロッド９に正電圧が印加されることにより，ガリウム原料液体３が陽極になる。他方，陰極室５内の電解液中には陰極板１１が浸漬され，これに負電圧が印加される。
【００２１】
陽極室４と陰極室５とは電解液１が連通する構成とするが，図例の装置では，陽極室４を形成している円筒状容器６の高さを電解液１の液面より低くなるように電解槽２内の一方の側方に設置することにより，電解液が両室４と５に連通するようにしてある。１２は両室４と５の間に配置された仕切板である。この仕切板１２の高さも円筒状容器６とほぼ同様にして電解液の液面より低くしてある。なお，仕切板１２と円筒状容器６との間に形成する空間部には蓋１３が施してあり，この蓋１３の下方空間は空洞となっている。陽極室４と陰極室５との間で電解液１が連通する構成とするには，この例に限られず，例えば，陽極室を形成する円筒状容器に隣接して独立した陰極室を作り，両室を区切る壁に連通路を設けるような構成でもよい。
【００２２】
円筒状容器６の外側下方に設置される磁石回転子７は，容器６の中心軸の周りに回転するように取付けられ，その回転はモータ１４によって付与される。この回転子７は永久磁石が用いられ，これが容器６の下方で容器軸を中心として水平面上を回転することにより，容器６内のガリウム原料液体３にはその磁力により同方向の回転力が付与されるので，容器軸を中心とした旋回流が発生し，この回転により遠心力が与えられる。
【００２３】
円筒状容器６内の中心部に設置されるサクションパイプ８は，その先端のサクション孔が，旋回しているガリウム原料液体３の中央表面部に位置するように，電解槽２の上方から電解液中に上下動可能に挿入されている。これにより，サクションパイプ８に負圧を発生させて吸引すると，原料液体２の中央表面部の物質が吸い込まれる。そのさい，原料液体２の極表層部の物質を吸い込むことができるように先端のサクション孔の位置を調節する。
【００２４】
旋回しているガリウム原料液体３の中央表面部には，遠心力によって，原料液体より比重の小さい物質１５（スカム）が集まるので，サクションパイプ８からはそのスカム１５を吸い出すことができる。そのさい，電解液１が同伴しても，さらには少量の原料液体３が同伴しても，同伴量が電解に差し支えない程度であれば，特に問題はない。
【００２５】
他方，陰極室５では，陰極板１１の表面にガリウム金属が析出するが，電解液の温度がガリウムの融点以上の温度に維持されることにより，析出したガリウム金属は液状となり，下方の受溜め１６に落下し，抜き出し口１７から精製ガリウムとして回収される。
【００２６】
このような装置構成において，図示の装置では，電解槽２の槽外に不溶性陽極１８と陰極１９をもつ補助電解槽２０を設け，電解槽２とこの補助電解槽２０の間を電解液１が循環する回路２１(a,b,c,d) が設けられている。
【００２７】
この補助電解槽２０は，電解液１中に溶存するガリウムを陰極１９で析出させることにより，電解液１中のガリウム濃度があまり高くならないようにするものであり，電解液１から過剰ガリウムの電解採取を行う。補助電解槽２０の陰極１９で析出したガリウム金属は，電解液がガリウムの融点温度以上に維持されていることにより，陰極１９から槽底部に滴下し，取り出し口２２から精製ガリウムとして採取される。
【００２８】
また，図示の装置では，電解槽２の槽外に，さらに中間槽２４が設置されている。この中間槽２４に，前記の補助電解槽２０を経た電解液を管路２１ｂを通じて供給すると共に，この中間槽２４と前記のサクションパイプ８とを管路２５で連結し，サクションパイプ８で吸引される流体物を中間槽２４に供給する。そして，中間槽２４から電解槽２に通ずる管路２１ｃには，フイルタ２６とポンプ２７が介装してある。すなわち，電解槽２のオーバーフロー電解液は，管路２１ａ→補助電解槽２０→管路２１ｂ→中間槽２４→管路２１ｃ→フイルタ２６→管路２１ｄを経て，電解槽２に戻る構成としてある。
【００２９】
サクションパイプ８から中間槽２４に至る管路２５にはポンプ２８が介装されており，このポンプ２８の駆動により，サクションパイプ８に負圧を発生させると共にサクションパイプ８に吸い込まれた流体（スカム１５＋電解液１＋原料液体３）を中間槽２４に送給する。そのさいポンプ２８の回転数制御や発停により，吸い出し量を調整することができ，また管路２５に流量調整弁（図示しない）を設けて流量を調整することもできる。もっとも，中間槽２４とサクションパイプ８との間に落差を設けておき，ポンプ２８によらずに，そのヘッドにより自然に該流体を中間槽２４に流し込むようにしてもよい。この場合には，管路２５に流量調整弁を設けて流量を調整する。
【００３０】
中間槽２４では，サクションパイプ８からのスカムと電解液および補助電解槽２０からの電解液を合流させるが，この流体が中間槽２４に滞留する間に，系全体の電解液の温度を調整する。このために，中間槽２４では加熱器３０と攪拌機３１を備えている。加熱器３０は，図示の例では投げ込みヒータが用いられており，液中に浸漬されたヒータ３２の通電量を調整することにより，槽内流体を所定温度に加熱する。攪拌機３１は掻き混ぜ羽根３３をモータで回転させて槽内流体に攪拌を付与する。
【００３１】
温度調整された槽内流体はポンプ２７により電解槽２に還流するが，その過程でフイルタ２６を経ることにより，流体中の懸濁物（スカム分）が濾別される。フイルタ２１の濾材としては図示の装置では活性炭を用いているが，ポリプロピレンやテフロン等からなる樹脂フイルタを用いることもでき，その他，５０℃で耐アルカリの素材であれば，特に限定されない。
【００３２】
フイルタ２１の濾液は管路２１ｄを経て電解槽２に戻されるが，管路２１ｄの吐出端３５を陽極室４の側（円筒状容器６）に配することにより，この流体を原料液体３の上部に投入する。この還流により，電解槽２内の電解液１の液面が電解中一定レベル（溢流口３６のレベル）に維持され且つ電解液の温度も所定の温度に維持される。
【００３３】
なお，電解槽２には，陽極室４の円筒状容器６にガリウム原料液体を電解中に補給するための原料補給チューブ３７が備えてある。このチューブ３７は取外し自在に設置されているが，原料補給時には注入端３８をガリウム原料液体３内に浸漬しながら液状ガリウム原料を注入する。
【００３４】
なお，図２において，電極板１１を中心軸として左半分のものを右側にも対照的に配置し，陰極室５を挟んでその両側に円筒状容器６をもつ陽極室４を設けた電解槽に構成すると，処理量を倍増させることができる。
【００３５】
次に，図示の装置を用いて本発明法を実施する場合の操作態様を説明する。
【００３６】
円筒状容器６と仕切板板１２の高さは特に限定されないが，電解液１の液面の１／３程度として，電解液１が陽極室４と陰極室５との間を自由に流通するようにするのがよい。電解液１にはＮａＯＨ水溶液を使用するが，ＮａＯＨ濃度は１００〜２００ｇ／Ｌ，さらに好ましくは１５０ｇ／Ｌ程度である。ＮａＯＨ濃度が１００ｇ／Ｌより低いと極間電圧が上がり，精製ガリウムの純度が下がるようになる。他方，２００ｇ／Ｌを超えると，液中に溶け込む不純物濃度が上がり，同じく精製ガリウムの純度が下がる。電解液の温度は３５〜７０℃が好ましく，さらに好ましくは５０〜６５℃である。３５℃より低いと極間電圧が上がり，７０℃を超えても特別に電解効率が上がる訳ではなく，電解槽の材質等に支障を与えることがある。この電解液の温度は図示の装置では，中間槽２４の加熱器３０で調節される。なお，金属ガリウムの融点は２９.９℃であるから，槽内の温度はこれ以上に維持されねばならない。
【００３７】
この電解液条件のもとで，陽極室４の円筒状容器６内に適量のガリウム原料液体３を入れ，磁石回転子７を回転して該原料液体３に遠心力を付与しながら，原料液体３を陽極として陰極板１１との間に通電を開始するが，電流密度が０.０２〜０.２Ａ／ｃｍ²，好ましくは０.０５〜０.１Ａ／ｃｍ²となるように通電する。電流密度が０.０２Ａ／ｃｍ²より低いと電解が進まず，０.２Ａ／ｃｍ²を超えると精製ガリウムの純度が下がるようになる。
【００３８】
電解中，磁石回転子７により原料液体３を中心軸回りに回転して遠心力を付与し続けると，ガリウム金属より比重の低い物質（スカム１５）が該原料液体３の表面中央部に集まってくる。このスカム１５の集まり状態が最も良好となるように磁石回転子７の回転数を制御し，原料液体３の回転状況を調節する。スカム１５は原料液体よりも黒色を呈するので，目視観察により，中央表面への集まり状態を知ることができる。
【００３９】
先述のように，この中央に集まったスカム１５には，ガリウム酸化物が含まれまた，原料液体３中の不純物の酸化物も若干含まれることがある。しかし，金は殆んど酸化しないので，金の酸化物が存在することはあり得ない筈であるが，実際にはサクションパイプ８でこのスカム１５を吸い上げると金も同伴するようになる。
【００４０】
中央に集まったスカム１５をサクションパイプ８で吸い上げるさいには，原料液体３は出来るだけ吸い上げないようにするために，サクションパイプ８の先端のサクション孔をスカム１５の若干上に位置させて，電解液１と共にスカム１５を吸い上げるようにするのがよい。これにより，不可避的に原料液体が同伴するものは仕方がないとして，発生するスカム１５の殆んどを電解液と共に吸い上げることができ，また金を同伴して吸い上げることができる。
【００４１】
図示の装置では，電解液と共に吸い上げられた金同伴のスカム１５は中間槽２４に入り，補助電解槽２０から中間槽２４に入る電解液と共に掻き混ぜられ且つ加熱器３０で加熱される。これにより，電解液中にスカムおよび金，更には少量のガリウム原料液体が混濁した所定温度の流体が得られる。この流体はフイルタ２６で懸濁物が濾別されたあと，電解槽２に戻されるが，この還流液の温度と流量は電解槽２で必要とする電解液の温度と量に応じられるように加熱器３０の操作とポンプ２７の回転数により調整される。この操作は自動制御で行うことができる。
【００４２】
この還流の過程でフイルタ２６において液中の懸濁分が濾別されるが，この濾別された物質には金が同伴する。ここで回収される金はガリウム原料液体中に混在した金の殆んどを占める。したがって，陽極残中の金濃度は極めて低くなり且つ陰極で析出する精製ガリウム中の金濃度も極めて低くなる。精製ガリウム中の金濃度が低くなることは，更に高純度ガリウムを得るための次工程の負荷を著しく低減することができる。本発明法で金が除去されていることは，６Ｎや７Ｎの高純度ガリウムを製造する上で非常に有利となる。
【００４３】
このようにして，ガリウム原料液体３中に混在した金はフイルタ２６で除去され，またガリウム原料液体３中に混在した不純物例えばＩｎ，Ｃｕ，Ｐｂ等は陽極残中に濃縮される。その結果，陰極室５の受溜め１６で回収される精製ガリウムには，Ａｕ，Ｉｎ，Ｃｕ，Ｐｂ等は殆んど混在せず，高純度の金属ガリウムとなる。
【００４４】
他方，ガリウム原料液体３の表面に発生する酸化物系のスカムが除去されることにより，これら酸化物被膜発生によるブレークアウト（電解中止）等のトラブル発生（酸化物被膜が絶縁層となり極間電圧の急激な上昇を招き，無理に電解を続けると純度の低いガリウムが陰極に電着する等）も未然に防止される。このため，原料補給チューブ３７からガリウム原料を補給して電解を続行しても，トラブルなく電解を進行させることができる。原料補給しながら電解を進行させると陽極残中の不純物濃度は高まることになるが，本発明法では表面部のスカムが除去される結果，よほど不純物濃度が高くならない限り，電解を続行することができる。
【００４５】
この電解続行の間，電解液の濃度管理は補助電解槽２０で行う。電解液中のガリウム濃度は電解中は徐々に増加してくるからである。電気量的には陽極・陰極とも同負荷で陽極から溶け出す量と陰極で電着する量とは同量で電解液中のガリウム濃度は一定に保たれるはずであるが，化学的には高温高アルカリ溶液なので陽極からは電気当量以上が溶出しまた陰極においてもいったん電着した精製ガリウムの再溶解により徐々に電解液中のガリウム濃度は増加してゆく。先述のように電解液中のガリウム濃度が高くなると，電解液中に不純物の溶出も始まるおそれがあるので，補助電解槽２０で電解液中のガリウムを陰極１９で析出させることにより，過剰に溶存しているガリウムを精製ガリウムとして採取する。補助電解槽２０においては，この電解槽２０を出る電解液中のガリウム濃度が所定の範囲例えば３０〜１５０ｇ／Ｌ，好ましくは３０〜１００ｇ／Ｌ，さらに好ましくは５０〜６０ｇ／Ｌとなるように，不溶性陽極１８と陰極１９の間に通電する通電量と通電時間を制御すればよい。この制御は自動化することができる。
【００４６】
このようにして，本発明によれば，電解中にガリウム原料を陽極に補給して長時間電解を続行しても，電解槽２の陰極１１さらには補助電解槽２０の陰極１９で析出して回収される精製ガリウム中への不純物の混入を回避でき，また陽極残にはＩｎ，Ｃｕ，Ｐｂ等の不純物濃度が高いものが得られ，且つ金もフイルタ２６で採取されるので，高い精製率のもとで生産性よく精製ガリウムを製造することができる。
【００４７】
【実施例】
〔実施例１〕
図１〜２に示した装置において，Ｇａ：５０ｇ／ＬおよびＮａＯＨ：１５０ｇ／Ｌを溶解した３５Ｌの電解液を電解槽２内に入れ，電解槽２→補助電解槽２０→中間槽２４→電解槽２の順に，ポンプ２７を駆動して，３００ｍＬ／ｍｉｎの流量で循環させた。そして，中間槽２４において加熱器３０と攪拌機３１のスイッチを入れ，電解槽２内の電解液の温度が５０℃となるように，加熱器２７での入熱量を，ヒータ附属のコントローラーで調節した。
【００４８】
次いで，予め溶融しておいた１０Ｋｇのガリウム原料液体３を陽極室４の円筒状容器６内に装入し，モータ１４を駆動して磁石回転子７を回動させ，ガリウム原料液体３に旋回流を起こさせて遠心力を与えた。この状態で，サクションパイプ８の先端のサクション孔が，原料液体３の中心部表面から約５ｍｍ高い位置となるように調整し，ポンプ２８を駆動して１５０ｍＬ／ｍｉｎの流量で吸引した。また，導電ロッド９の先端の金属端子１０が常時ガリウム原料液体３内に浸漬されるようにセットした。この状態で，ステンレス鋼板製の陰極板１１との間で，電流密度が０.１０Ａ／ｃｍ²で通電を開始し，８７９時間連続で電解を行った。その間，原料補給チューブ３７から溶融したガリウム原料液体を２４回に分けて合計４３.７Ｋｇ補給した。また，補助電解槽２０では，通電量６Ａのもとで通電の発停を行うことにより，電解液中のガリウム濃度が５０〜６０ｇ／Ｌの範囲に収まるようにガリウムの電解採取を行った。
【００４９】
電解の間，ポンプ２７と２８の送液量は前記の量にほぼ維持し続け，サクションパイプ８は中央部に集まるスカム１５より約５ｍｍ高い位置に維持されるように上下位置を調整した。フイルタ２６の濾材には活性炭を用いた。
【００５０】
本例の操業結果を表１に示した。
【００５１】
【表１】

【００５２】
表１の結果に見られるように，得られた精製ガリウム量は，電解槽２と補助電解槽２０と合わせて，原料ガリウム量に対して９０％近くまで回収できたが，まだ電解は可能であった。また，得られた精製ガリウムの不純物については，インジウムで７ｐｐｍ，金は０.１ｐｐｍ以下，銅と鉛については０.５ｐｐｍ以下にまで低減でき，ガリウム品位として４〜５Ｎ（９９．９９９％）クラスであった。
【００５３】
〔実施例２〕
不純物量の多いガリウム原料を用いた以外は，実施例１と同様に処理した。ただし，電解時間は３９５時間まで行った。その間，溶融したガリウム原料液体を１０回に分けて合計１２.２Ｋｇ補給した。操業結果を表２に示した。
【００５４】
【表２】

【００５５】
表２は，特にＩｎ濃度の高いガリウム原料を用いて，陽極のガリウム原料液体中にＩｎ濃度を限界まで濃縮する電解を行った結果を示すものであるが，陽極残にはＩｎを８８％近くまで濃縮できたことを示している。電解終了付近では陽極は導電ロッド９の近傍を除いて灰色の固形物状態を示した。精製ガリウム中のＩｎ濃度は８００ｐｐｍ付近となったが，銅と鉛については検出値以下であった。この結果から，本発明法は非常にＩｎ濃度の高いガリウム原料からの精製に有効であることがわかる。
【００５６】
〔実施例３〕
実施例２で得られた精製ガリウムを原料として，実施例１と同様に処理した。電解時間は３６０時間連続であり，その間，１０回に分けて合計１１.８Ｋｇの原料を液体状態で補給した。操業結果を表３に示した。
【００５７】
【表３】

【００５８】
表３の結果に見られるように，得られた精製ガリウムの不純物は，インジウムで２ｐｐｍ以下，銅と鉛については０.５ｐｐｍ以下にまで低減でき，ガリウム品位として５Ｎ（９９．９９９％）クラスとなった。また精製ガリウム量は，電解槽２と補助電解槽２０と合わせて，９０％近くまで回収できた。
【００５９】
一方，実施例２の陽極残としてＩｎの高いものが得られているので，実施例２と３を組み合わせると，高濃度でＩｎを含むガリウム原料からＩｎを効率よく分離して高品位のガリウムを得ることができることになる。
【００６０】
以上の実施例に見られるように，実操業においては，これらの実施例を組み合わせると，非常に生産効率の良いラインが完成できる。例えば，不純物のインジウムを２，０００ｐｐｍ含有したガリウム原料１００ｋｇから５Ｎクラスのガリウムを生産する場合，まず実施例１から精製ガリウム９０ｋｇが得られる。またインジウムを２０,０００ｐｐｍまで濃縮された陽極残ガリウム１０ｋｇからは実施例２のとおり３Ｎクラスのガリウム９.７ｋｇ得られる。不純物が８０％まで濃縮されたもの約０.３ｋｇはブリードオフされ，別方法でガリウムの回収を行う。３Ｎクラスのガリウム９.７ｋｇは最初の工程に戻され, ５Ｎクラスのガリウムが８.８ｋｇ程度得られる。すなわち, これらの工程から９８.８％の５Ｎクラスの回収が見込まれる。
【００６１】
〔比較例〕
補助電解槽２０での電解採取を行わず，また磁石回転子７を回転させず（モータ１４を駆動させず）且つサクションパイプ８から吸液しない（ポンプ２８を停止）状態として，原料液体に遠心力を付与せず且つスカムも排出しなかった以外は実施例１と同様の条件で電解を行ない（フイルタ２６も使用しない），電解液のガリウム濃度の変化と，この変化に対する電流効率および電解液中のＩｎ濃度を測定した。その結果を表４に示した。
【００６２】
【表４】

【００６３】
表４の結果に見られるように，電解液中のガリウム濃度は適切な範囲に維持されないと，電解効率が低くなり，また電解液中にＩｎが溶出してくることがわかる。
【００６４】
【発明の効果】
以上述べたように，本発明によれば，従来のガリウムの電解精製法では除去できなかった金等の不純物の除去ができかつ陽極への原料補給も可能である。そして，陽極残中への不純物の濃縮度を上昇させることができ，電解寿命を延ばすことができる結果，精製ガリウムの収率が向上し且つその精製効率も向上させることができる。したがって，亜鉛製錬工程から生産されたガリウム原料や化合物半導体スクラップから回収された粗ガリウム，更には高純度ガリウム精製工程より発生する不純物含有率の高いガリウム原料からのガリウム精製に多大の貢献ができる。
【図面の簡単な説明】
【図１】本発明法を実施する装置の例を示す略断面図である。
【図２】図１の装置の電解槽部分の略平面図である。
【符号の説明】
１電解液
２電解槽
３ガリウム液体原料
４陽極室
５陰極室
６円筒状容器
７磁石回転子
８サクションパイプ
９導電ロッド
１０金属端子
１１陰極板
１２仕切板
１５ガリウム液体原料の表面中央部に集まったスカム
１７精製ガリウム抜き出し口
２０補助電解槽
２１循環回路
２４中間槽
２５サクションパイプと中間槽を連結する管路
２６フイルタ
３０加熱器
３７原料補給チューブ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for electrolytic purification of gallium.
[0002]
[Prior art]
The demand for gallium metal is increasing as a raw material for compound semiconductor devices such as GaAs and GaP and light emitting devices. Gallium is mainly produced as a by-product of the alumina manufacturing process and zinc smelting, but semiconductor scrap is also a gallium raw material.
[0003]
As such a gallium purification method from a gallium raw material, a crystal purification method, a single crystal pulling method and an electrolytic purification method are well known.
[0004]
The crystal refining method is a method in which a seed crystal is made to exist on the cooling medium side of molten gallium metal and the seed crystal is grown by the cooling effect of the cooling medium to obtain purified solid gallium on the grown crystal side. For example, Japanese Patent Laid-Open No. 2-50926 discloses a crystal purification method in which such crystal growth is performed in multiple stages.
[0005]
The single crystal pulling method is a purification method in which the tip of a seed crystal is brought into contact with molten gallium metal, and the single crystal from which impurities are removed is slowly pulled up. For example, JP-A-2-243727 teaches that, in this method, if an acidic solution layer is formed on the surface of molten gallium, the purification efficiency is improved.
[0006]
The electrolytic refining method utilizes the property that when a gallium source is energized as an anode, gallium and electrochemically base metals are eluted in the electrolyte and gallium and noble metals are electrodeposited at the cathode. This is a method for obtaining purified gallium metal at the cathode. For example, in JP-A-6-192877, when a gallium raw material liquid is placed at the bottom of an electrolytic cell and electrolysis is performed between the raw material liquid and a rod-shaped cathode, the gallium metal deposited on the surface of the cathode is granular. It is taught that impurities such as indium, copper and lead in the gallium raw material are left on the anode side while being dropped and collected in a lower receiver.
[0007]
[Problems to be solved by the invention]
In the crystal refining method, gallium metal of 5N or more (99.999% or more) is applied as a raw material to be processed because gallium purity does not increase unless it is repeatedly operated, and the process is complicated and productivity is not good. In many cases, this is limited to the application in the high-purity region where it is purified to 6N or 7N or more (99.9999% or 99.99999999% or more), and the yield of raw materials having a purity of about 2N or 3N is poor. Not suitable. In addition, the single crystal pulling method is similarly limited to application in a high purity region, and there is a problem that the equipment is expensive.
[0008]
On the other hand, the electrolytic purification method is simpler than the previous two methods, requires almost no manual operation, and is inexpensive, so it can be used as a low-purity purification method as a link to high-purity purification. There is an advantage that it is possible. However, the conventional electrolytic purification method is to leave indium, copper, lead, etc. concentrated in the anode, and when more than a predetermined amount of impurities are concentrated in the anode, the impurities enter the electrolyte and deposit on the cathode. This results in a decrease in gallium purity. Therefore, when the purity of purified gallium is regulated, the electrolysis life is naturally determined. Further, the conventional electrolytic refining method has a problem that “gold” mixed in semiconductor scrap or the like cannot be removed.
[0009]
[Problems to be solved by the invention]
Therefore, the present invention is capable of removing impurities such as gold, which could not be removed by the conventional method, in the gallium electrolytic refining method, which is inexpensive and simple in process, and requires almost no manual operation. The purpose of this study is to develop a gallium electrolytic purification method that can increase the concentration of gallium and extend the electrolysis lifetime, and to purify gallium in a high yield.
[0010]
[Means for Solving the Problems]
According to the present invention, in a gallium electrolytic purification method in which a gallium raw material liquid is used as an anode and purified gallium is deposited in an electrolytic solution on a cathode, an operation for discharging scum generated on the anode surface to the outside of the electrolytic cell, and completion of electrolysis A method for electrolytically purifying gallium is provided, in which an operation for replenishing the gallium raw material liquid for the anode is performed, and further an operation for maintaining the gallium concentration in the electrolytic solution within a predetermined range during electrolysis.
[0011]
Further, according to the present invention, the anode chamber containing the gallium raw material liquid as an anode and the cathode chamber for collecting purified gallium deposited on the cathode are passed between the anode chamber and the cathode chamber. Thus, in the gallium electrolysis apparatus in which the electrolyte solution is placed, the anode chamber is configured in a cylindrical container, a magnet rotor is installed on the lower outside of the cylindrical container, and a suction pipe is installed in the center of the cylindrical container. And an auxiliary electrolytic cell having an insoluble anode and a cathode is provided outside the electrolytic device, and a circuit for circulating the electrolytic solution between the electrolytic device and the auxiliary electrolytic cell is provided. The gallium electrolytic purification apparatus is characterized in that the suction pipe is connected to the intermediate tank, and a filter is interposed in a pipe line extending from the intermediate tank to the electrolysis apparatus.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As a result of intensive studies and researches to solve the above-mentioned problems, the present inventors have made electrolytic gallium metal using a molten gallium metal containing impurities (referred to as a gallium raw material liquid) as an anode and depositing a high purity gallium metal at the cathode. In this method, if the scum formed on the anode surface is discharged out of the electrolytic cell together with a part of the electrolytic solution, the electrolysis can be continued even if the impurity concentration in the anode residue increases, and therefore, the electrolytic life It has been found that can be significantly improved. It was also found that the gold entrained in the gallium raw material can be removed by the operation of discharging this scum. Since electrolysis can be continued even when the impurity concentration in the anode is high, it becomes possible to perform electrolysis while replenishing the gallium raw material liquid of the anode, and purified gallium can be obtained with a high yield. At that time, if the gallium concentration in the electrolytic solution is made constant, the electrolysis life can be further extended.
[0013]
When the gallium raw material liquid in the electrolyte is rotated (turned), a substance exhibiting black color gathers on the surface of the liquid at the center of rotation. Since this substance exhibits black color, it can be regarded as containing gallium oxide. If scum is collected at the center of rotation of the anode using centrifugal separation, and the scum is sucked out by a suction pipe, the oxide film generated at the interface between the gallium raw material liquid and the electrolyte can be easily removed, and gold is also removed. It has special effects in what it can do. This is because the formation of the oxide film extremely deteriorates the electrolysis efficiency, and gold cannot be separated by a normal gallium electrolysis purification method.
[0014]
The inventors of the present invention have found that when scum gathered on the surface of the gallium raw material liquid at the rotation center is sucked out using a suction pipe, surprisingly, gold is accompanied and sucked out. The reason for this is not necessarily clear, but as the electrolysis progresses, a gallium oxide is mainly formed on the surface of the raw material liquid, and this oxide has the property of taking up gold more easily than the liquid phase of the raw gallium. It is thought that there is.
[0015]
In normal electrolysis, gold accompanying the gallium raw material liquid does not remain in the anode residue (anode slime) as shown in a comparative example described later. From the standard electrode potential, gold falls into the most noble classification. Electrochemically, the electrolytic potential of gallium does not dissolve into the liquid from the anode (does not ionize). Nevertheless, the anode remains, so it is thought that for some reason, it will be dispersed in the electrolyte in a colloidal form. And, it seems that the gold fine particles floating in the electrolyte solution in this colloidal state are entrained when gallium ions are electrodeposited at the cathode, and are entrained in the purified gallium.
[0016]
As described above, the gold accompanying the gallium raw material was difficult to remove by electrolytic refining. However, according to the present invention, the gold can be extracted along with the scum through the suction pipe, and the removal of the gold is very easy. It became. Other impurities, such as In, Cu, Pb, etc., behave differently from gold and are concentrated as the anode residue.
[0017]
Also, by removing scum from the anode surface, it becomes possible to continue the electrolysis even if impurities in the gallium source are concentrated at a high concentration in the anode residue, and a new gallium source liquid is added during the electrolysis. Even if it is replenished, electrolysis can be continued without any problem. At that time, if the gallium concentration in the electrolytic solution becomes too high, impurities in the anode also dissolve in the electrolytic solution, so that the gallium concentration in the electrolytic solution is 150 g / L or less, preferably 100 g / L or less, more preferably 60 g / L. It is good to maintain below L. Therefore, the gallium in the electrolyte is electrolyzed by circulating the electrolyte in an electrolytic collection tank installed outside the electrolytic tank and depositing gallium in the electrolyte on the cathode of the electrolytic collection tank. It is desirable to collect.
[0018]
However, if the gallium concentration in the electrolytic solution is too low, the current efficiency (amount of electrodeposited metal / theoretical electrodeposited metal amount) decreases, so the gallium concentration in the electrolytic solution is maintained at 30 g / L or more, preferably 50 g / L or more. It is desirable to do. When the concentration is less than 30 g / L, the current efficiency falls below 80%. Therefore, the gallium concentration in the electrolytic solution should be maintained at 30 to 150 g / L, preferably 30 to 100 g / L, and more preferably 50 to 60 g / L.
[0019]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of an apparatus for carrying out the method of the present invention, and FIG. 2 shows a schematic plane of an electrolytic cell of the apparatus.
[0020]
This apparatus divides the inside of an electrolytic cell 2 containing an electrolytic solution 1 into an anode chamber 4 that contains a gallium raw material liquid 3 as an anode and a cathode chamber 5 that collects purified gallium deposited on the cathode. The chamber 4 is formed of a cylindrical container 6, a magnet rotor 7 is installed on the outside of the cylindrical container 6, and a suction pipe 8 is arranged in the center of the cylindrical container 6. Ideally, the cylindrical container 6 has a perfect circle on the inner wall, but in some cases, it may be a polygon with a corner, or it may have an inner surface with different radii in the vertical direction. Also good. Reference numeral 9 denotes a conductive rod with insulation coating. When the metal terminal 10 attached to the tip of the conductive rod 9 is immersed in the gallium raw material liquid 3 and a positive voltage is applied to the conductive rod 9, the gallium raw material liquid 3 becomes an anode. On the other hand, the cathode plate 11 is immersed in the electrolytic solution in the cathode chamber 5, and a negative voltage is applied thereto.
[0021]
The anode chamber 4 and the cathode chamber 5 are configured so that the electrolyte solution 1 communicates with each other. However, in the illustrated apparatus, the height of the cylindrical container 6 forming the anode chamber 4 is lower than the liquid surface of the electrolyte solution 1. The electrolytic solution is communicated with both the

chambers

4 and 5 by being installed on one side of the electrolytic cell 2 as described above. A partition plate 12 is disposed between the

chambers

4 and 5. The height of the partition plate 12 is made lower than the liquid level of the electrolytic solution in substantially the same manner as the cylindrical container 6. A space 13 formed between the partition plate 12 and the cylindrical container 6 is provided with a lid 13, and the space below the lid 13 is a cavity. The configuration in which the electrolytic solution 1 communicates between the anode chamber 4 and the cathode chamber 5 is not limited to this example. For example, an independent cathode chamber is formed adjacent to the cylindrical container forming the anode chamber, A configuration in which a communication path is provided on the wall separating the two chambers may be used.
[0022]
A magnet rotor 7 installed on the outer lower side of the cylindrical container 6 is attached so as to rotate around the central axis of the container 6, and the rotation is applied by a motor 14. The rotor 7 uses a permanent magnet, which rotates on a horizontal plane around the container axis below the container 6, so that the gallium source liquid 3 in the container 6 is given a rotational force in the same direction due to its magnetic force. Therefore, a swirl flow around the container axis is generated, and centrifugal force is given by this rotation.
[0023]
The suction pipe 8 installed at the center of the cylindrical container 6 has an electrolyte solution from above the electrolytic cell 2 so that the suction hole at the tip of the suction pipe 8 is located at the center surface of the rotating gallium raw material liquid 3. It is inserted so that it can move up and down. Thereby, when a negative pressure is generated in the suction pipe 8 and sucked, the substance on the central surface portion of the raw material liquid 2 is sucked. At that time, the position of the suction hole at the tip is adjusted so that the material of the extreme surface layer of the raw material liquid 2 can be sucked.
[0024]
Since the substance 15 (scum) having a specific gravity smaller than that of the raw material liquid is collected by the centrifugal force at the center surface portion of the rotating gallium raw material liquid 3, the scum 15 can be sucked out from the suction pipe 8. At that time, even if the electrolytic solution 1 is accompanied, or even if a small amount of the raw material liquid 3 is accompanied, there is no particular problem as long as the accompanying amount does not interfere with the electrolysis.
[0025]
On the other hand, in the cathode chamber 5, gallium metal is deposited on the surface of the cathode plate 11, but when the temperature of the electrolyte is maintained at a temperature equal to or higher than the melting point of gallium, the deposited gallium metal becomes liquid and is received in the lower reservoir. 16 is recovered as purified gallium from the extraction port 17.
[0026]
In such an apparatus configuration, in the illustrated apparatus, an auxiliary electrolytic cell 20 having an insoluble anode 18 and a cathode 19 is provided outside the electrolytic cell 2, and the electrolytic solution 1 is interposed between the electrolytic cell 2 and the auxiliary electrolytic cell 20. A circulating circuit 21 (a, b, c, d) is provided.
[0027]
This auxiliary electrolytic cell 20 deposits gallium dissolved in the electrolytic solution 1 at the cathode 19 so that the gallium concentration in the electrolytic solution 1 does not become so high. Collect. Gallium metal deposited at the cathode 19 of the auxiliary electrolytic cell 20 is dropped from the cathode 19 to the bottom of the cell and is collected as purified gallium from the take-out port 22 because the electrolytic solution is maintained at a melting point temperature or higher of gallium.
[0028]
In the illustrated apparatus, an intermediate tank 24 is further provided outside the electrolytic cell 2. The intermediate tank 24 is supplied with the electrolytic solution having passed through the auxiliary electrolytic tank 20 through a pipe line 21b, and the intermediate tank 24 and the suction pipe 8 are connected by a pipe line 25 and sucked by the suction pipe 8. The fluid is supplied to the intermediate tank 24. In addition, a filter 26 and a pump 27 are interposed in a pipe line 21 c that leads from the intermediate tank 24 to the electrolytic cell 2. That is, the overflow electrolytic solution in the electrolytic cell 2 returns to the electrolytic cell 2 through the pipeline 21a → the auxiliary electrolytic cell 20 → the pipeline 21b → the intermediate vessel 24 → the pipeline 21c → the filter 26 → the pipeline 21d.
[0029]
A pump 28 is interposed in a pipe line 25 extending from the suction pipe 8 to the intermediate tank 24. By driving the pump 28, negative pressure is generated in the suction pipe 8 and fluid (scum) sucked into the suction pipe 8 is drawn. 15 + electrolytic solution 1 + raw material liquid 3) is fed to the intermediate tank 24. At that time, the amount of suction can be adjusted by controlling the number of revolutions of the pump 28 and starting and stopping, and the flow rate can be adjusted by providing a flow rate adjusting valve (not shown) in the pipe 25. However, a drop may be provided between the intermediate tank 24 and the suction pipe 8, and the fluid may naturally flow into the intermediate tank 24 by the head without using the pump 28. In this case, a flow rate adjusting valve is provided in the pipe line 25 to adjust the flow rate.
[0030]
In the intermediate tank 24, the scum from the suction pipe 8, the electrolytic solution, and the electrolytic solution from the auxiliary electrolytic tank 20 are merged. While this fluid stays in the intermediate tank 24, the temperature of the electrolytic solution in the entire system is adjusted. . For this purpose, the intermediate tank 24 includes a heater 30 and a stirrer 31. The heater 30 uses a throwing heater in the illustrated example, and heats the fluid in the tank to a predetermined temperature by adjusting the energization amount of the heater 32 immersed in the liquid. The stirrer 31 rotates the stirring blade 33 with a motor to apply stirring to the fluid in the tank.
[0031]
The temperature-adjusted fluid in the tank is returned to the electrolytic cell 2 by the pump 27, and the suspension (scum content) in the fluid is filtered by passing through the filter 26 in the process. As the filter medium of the filter 21, activated carbon is used in the illustrated apparatus, but a resin filter made of polypropylene, Teflon, or the like can be used, and any other material that is resistant to alkali at 50 ° C. is not particularly limited.
[0032]
The filtrate of the filter 21 is returned to the electrolytic cell 2 through the pipe line 21d. By arranging the discharge end 35 of the pipe line 21d on the anode chamber 4 side (cylindrical container 6), this fluid is supplied to the raw material liquid 3. Throw in the top. By this reflux, the liquid level of the electrolytic solution 1 in the electrolytic cell 2 is maintained at a constant level (level of the overflow port 36) during electrolysis, and the temperature of the electrolytic solution is also maintained at a predetermined temperature.
[0033]
The electrolytic cell 2 is provided with a raw material supply tube 37 for supplying a gallium raw material liquid to the cylindrical container 6 of the anode chamber 4 during electrolysis. Although this tube 37 is detachably installed, the liquid gallium raw material is injected while the injection end 38 is immersed in the gallium raw material liquid 3 when the raw material is replenished.
[0034]
In FIG. 2, the left half of the electrode plate 11 as a central axis is also arranged on the right side, and the electrolytic cell is provided with anode chambers 4 having cylindrical vessels 6 on both sides of the cathode chamber 5 sandwiched between them. If configured, the processing amount can be doubled.
[0035]
Next, an operation mode when the method of the present invention is carried out using the illustrated apparatus will be described.
[0036]
The height of the cylindrical container 6 and the partition plate 12 is not particularly limited, but the electrolytic solution 1 freely flows between the anode chamber 4 and the cathode chamber 5 as about 1/3 of the liquid level of the electrolytic solution 1. It is better to do so. The electrolytic solution 1 uses an aqueous NaOH solution, and the NaOH concentration is about 100 to 200 g / L, more preferably about 150 g / L. When the NaOH concentration is lower than 100 g / L, the interelectrode voltage increases and the purity of the purified gallium decreases. On the other hand, if it exceeds 200 g / L, the concentration of impurities dissolved in the liquid increases, and the purity of the purified gallium also decreases. The temperature of the electrolytic solution is preferably 35 to 70 ° C, more preferably 50 to 65 ° C. When the temperature is lower than 35 ° C., the voltage between the electrodes increases, and even when the temperature exceeds 70 ° C., the electrolytic efficiency does not particularly increase, and the material of the electrolytic cell may be hindered. The temperature of the electrolytic solution is adjusted by the heater 30 of the intermediate tank 24 in the illustrated apparatus. Since the melting point of metal gallium is 29.9 ° C., the temperature in the tank must be maintained higher than this.
[0037]
Under this electrolytic solution condition, an appropriate amount of the gallium raw material liquid 3 is placed in the cylindrical container 6 of the anode chamber 4, and the raw material liquid 3 is rotated while rotating the magnet rotor 7 to apply centrifugal force to the raw material liquid 3. 3 is used as an anode, and energization is started between the cathode plate 11 and the current density is 0.02 to 0.2 A / cm. ² , Preferably 0.05 to 0.1 A / cm ² Energize so that Current density is 0.02 A / cm ² If it is lower, electrolysis does not proceed and 0.2 A / cm. ² Exceeding the purity of the purified gallium decreases.
[0038]
During electrolysis, when the raw material liquid 3 is rotated about the central axis by the magnet rotor 7 and the centrifugal force is continuously applied, a substance (scum 15) having a specific gravity lower than that of gallium metal gathers at the center of the surface of the raw material liquid 3. come. The rotational speed of the magnet rotor 7 is controlled so that the gathering state of the scum 15 is the best, and the rotational state of the raw material liquid 3 is adjusted. Since the scum 15 is blacker than the raw material liquid, the gathering state on the center surface can be known by visual observation.
[0039]
As described above, the scum 15 gathered in the center may contain some oxides of impurities in the raw material liquid 3 containing gallium oxide. However, since gold hardly oxidizes, it is unlikely that gold oxide will be present, but in reality, when the scum 15 is sucked up by the suction pipe 8, the gold is also accompanied.
[0040]
When the scum 15 collected in the center is sucked up by the suction pipe 8, the suction hole at the tip of the suction pipe 8 is positioned slightly above the scum 15 in order to prevent the raw material liquid 3 from being sucked up as much as possible. It is preferable to suck up the scum 15 together with the liquid 1. As a result, it is unavoidable that the raw material liquid is inevitably accompanied, so that most of the generated scum 15 can be sucked up together with the electrolyte, and can be sucked up with gold.
[0041]
In the illustrated apparatus, the gold-entrained scum 15 sucked up together with the electrolytic solution enters the intermediate tank 24, is agitated with the electrolytic solution entering the intermediate tank 24 from the auxiliary electrolytic tank 20, and is heated by the heater 30. As a result, a fluid having a predetermined temperature in which scum and gold, and a small amount of gallium raw material liquid are turbid in the electrolytic solution is obtained. This fluid is returned to the electrolytic cell 2 after the suspended matter is filtered by the filter 26, and the temperature and flow rate of the reflux liquid are adjusted according to the temperature and amount of the electrolytic solution required in the electrolytic cell 2. It is adjusted by the operation of the heater 30 and the rotational speed of the pump 27. This operation can be performed by automatic control.
[0042]
During this refluxing process, the suspended matter in the liquid is filtered off in the filter 26, and the filtered material is accompanied by gold. The gold collected here occupies most of the gold mixed in the gallium raw material liquid. Therefore, the gold concentration in the anode residue is extremely low, and the gold concentration in the purified gallium deposited at the cathode is also extremely low. Lowering the gold concentration in the purified gallium can significantly reduce the load of the next process for obtaining higher purity gallium. The removal of gold by the method of the present invention is very advantageous in producing 6N or 7N high-purity gallium.
[0043]
In this manner, gold mixed in the gallium raw material liquid 3 is removed by the filter 26, and impurities mixed in the gallium raw material liquid 3, such as In, Cu, and Pb, are concentrated in the anode residue. As a result, the purified gallium recovered in the reservoir 16 of the cathode chamber 5 contains almost no Au, In, Cu, Pb, etc., and becomes high-purity metallic gallium.
[0044]
On the other hand, the oxide-based scum generated on the surface of the gallium raw material liquid 3 is removed, thereby causing troubles such as breakout (discontinuation of electrolysis) due to the generation of these oxide films (the oxide film becomes an insulating layer and the interelectrode voltage If the electrolysis is continued forcibly, low-purity gallium is electrodeposited on the cathode. For this reason, even if a gallium raw material is replenished from the raw material replenishment tube 37 and electrolysis is continued, electrolysis can proceed without any trouble. If the electrolysis proceeds while replenishing the raw material, the concentration of impurities in the anode residue will increase. However, in the method of the present invention, as a result of removing the scum on the surface, electrolysis may be continued unless the impurity concentration becomes very high. it can.
[0045]
While this electrolysis is continued, the concentration control of the electrolytic solution is performed in the auxiliary electrolytic cell 20. This is because the gallium concentration in the electrolytic solution gradually increases during electrolysis. In terms of quantity of electricity, both the anode and cathode should dissolve at the same load from the anode, and the amount deposited at the cathode should be the same, and the gallium concentration in the electrolyte should be kept constant. Since it is a high-temperature, high-alkaline solution, more than an electrical equivalent is eluted from the anode, and the concentration of gallium in the electrolyte gradually increases due to redissolution of purified gallium once electrodeposited at the cathode. As described above, when the gallium concentration in the electrolytic solution becomes high, the elution of impurities may start in the electrolytic solution, so that the gallium in the electrolytic solution is deposited at the cathode 19 in the auxiliary electrolytic cell 20 to be dissolved excessively. The collected gallium is collected as purified gallium. In the auxiliary electrolytic cell 20, the gallium concentration in the electrolytic solution leaving the electrolytic cell 20 is within a predetermined range, for example, 30 to 150 g / L, preferably 30 to 100 g / L, and more preferably 50 to 60 g / L. The energization amount and energization time between the insoluble anode 18 and the cathode 19 may be controlled. This control can be automated.
[0046]
Thus, according to the present invention, even if electrolysis is continued for a long time by supplying a gallium raw material to the anode during electrolysis, it is deposited on the cathode 11 of the electrolytic cell 2 and further on the cathode 19 of the auxiliary electrolytic cell 20. Impurities can be prevented from being mixed into the recovered purified gallium, and the anode residue having a high impurity concentration such as In, Cu, Pb, etc. is obtained, and gold is also collected by the filter 26, so that a high purification rate is obtained. Can produce purified gallium with high productivity.
[0047]
【Example】
[Example 1]
In the apparatus shown in FIGS. 1 and 2, 35 L of electrolytic solution in which Ga: 50 g / L and NaOH: 150 g / L are dissolved is placed in the electrolytic cell 2, and the electrolytic cell 2 → auxiliary electrolytic cell 20 → intermediate cell 24 → electrolysis The pump 27 was driven in the order of the tank 2 and circulated at a flow rate of 300 mL / min. Then, the heater 30 and the stirrer 31 are switched on in the intermediate tank 24, and the amount of heat input in the heater 27 is adjusted by the controller attached to the heater so that the temperature of the electrolyte in the electrolytic tank 2 is 50 ° C. .
[0048]
Next, 10 Kg of gallium raw material liquid 3 previously melted is placed in the cylindrical container 6 of the anode chamber 4, the motor 14 is driven to rotate the magnet rotor 7, and the gallium raw material liquid 3 is swung. A centrifugal force was applied by causing a flow. In this state, the suction hole at the tip of the suction pipe 8 was adjusted so as to be about 5 mm higher than the surface of the central portion of the raw material liquid 3, and the pump 28 was driven to suck at a flow rate of 150 mL / min. The metal terminal 10 at the tip of the conductive rod 9 was set so as to be constantly immersed in the gallium raw material liquid 3. In this state, the current density is 0.10 A / cm with the cathode plate 11 made of stainless steel plate. ² Then, energization was started and electrolysis was performed continuously for 879 hours. In the meantime, the molten gallium raw material liquid was supplied from the raw material supply tube 37 in 24 times, and a total of 43.7 kg was supplied. In addition, in the auxiliary electrolytic cell 20, electrolysis of gallium was performed so that the gallium concentration in the electrolytic solution was within the range of 50 to 60 g / L by starting and stopping the energization under the energization amount 6A.
[0049]
During the electrolysis, the pumping amounts of the

pumps

27 and 28 were kept substantially at the above-mentioned amount, and the vertical position was adjusted so that the suction pipe 8 was maintained at a position about 5 mm higher than the scum 15 gathered at the center. Activated carbon was used as the filter medium of the filter 26.
[0050]
The operation results of this example are shown in Table 1.
[0051]
[Table 1]

[0052]
As can be seen from the results in Table 1, the amount of purified gallium obtained can be recovered to nearly 90% of the raw material gallium together with the electrolytic cell 2 and the auxiliary electrolytic cell 20, but electrolysis is still possible. there were. In addition, impurities in the obtained purified gallium can be reduced to 7 ppm for indium, 0.1 ppm or less for gold, and 0.5 ppm or less for copper and lead. The gallium quality is 4 to 5N (99.999%) class. Met.
[0053]
[Example 2]
The same treatment as in Example 1 was performed except that a gallium raw material having a large amount of impurities was used. However, the electrolysis time was up to 395 hours. Meanwhile, the molten gallium raw material liquid was divided into 10 times and a total of 12.2 kg was supplied. The operation results are shown in Table 2.
[0054]
[Table 2]

[0055]
Table 2 shows the results of electrolysis in which the In concentration is concentrated to the limit in the gallium raw material liquid of the anode using a gallium raw material having a particularly high In concentration. It was shown that it could be concentrated. Near the end of electrolysis, the anode showed a gray solid state except for the vicinity of the conductive rod 9. The In concentration in the purified gallium was around 800 ppm, but copper and lead were below the detected value. From this result, it can be seen that the method of the present invention is effective for purification from a gallium raw material having a very high In concentration.
[0056]
Example 3
Using the purified gallium obtained in Example 2 as a raw material, the same treatment as in Example 1 was performed. Electrolysis time was continuous for 360 hours, and during that time, a total of 11.8 kg of raw material was replenished in a liquid state divided into 10 times. The operation results are shown in Table 3.
[0057]
[Table 3]

[0058]
As can be seen from the results in Table 3, the impurities of the purified gallium obtained can be reduced to 2 ppm or less for indium and 0.5 ppm or less for copper and lead, and the gallium quality is 5N (99.999%) class. became. The amount of purified gallium was recovered to nearly 90% in combination with the electrolytic cell 2 and the auxiliary electrolytic cell 20.
[0059]
On the other hand, since a high In content is obtained as the anode residue in Example 2, combining Examples 2 and 3 efficiently separates In from a gallium raw material containing In at a high concentration, thereby converting high-quality gallium. Will be able to get.
[0060]
As can be seen from the above embodiments, in actual operation, a combination of these embodiments can complete a line with very high production efficiency. For example, when producing 5N class gallium from 100 kg of gallium raw material containing 2,000 ppm of indium as an impurity, 90 kg of purified gallium is first obtained from Example 1. Further, 9.7 kg of 3N class gallium can be obtained from 10 kg of residual anode gallium enriched with indium to 20,000 ppm as in Example 2. About 0.3 kg of impurities concentrated to 80% are bleed-off, and gallium is recovered by another method. 9.7 kg of 3N class gallium is returned to the first step, and about 8.8 kg of 5N class gallium is obtained. In other words, 98.8% of 5N class recovery is expected from these processes.
[0061]
[Comparative Example]
Electrolysis is not performed in the auxiliary electrolytic cell 20, and the magnet rotor 7 is not rotated (the motor 14 is not driven) and liquid is not absorbed from the suction pipe 8 (pump 28 is stopped). Electrolysis was performed under the same conditions as in Example 1 except that no force was applied and scum was not discharged (the filter 26 was not used), the change in the gallium concentration of the electrolyte, the current efficiency against this change, and the electrolyte The concentration of In was measured. The results are shown in Table 4.
[0062]
[Table 4]

[0063]
As can be seen from the results in Table 4, it can be seen that if the gallium concentration in the electrolytic solution is not maintained within an appropriate range, the electrolytic efficiency is lowered and In is eluted in the electrolytic solution.
[0064]
【The invention's effect】
As described above, according to the present invention, impurities such as gold, which could not be removed by the conventional gallium electrolytic purification method, can be removed, and the material can be supplied to the anode. As a result, the concentration of impurities in the anode residue can be increased and the electrolytic life can be extended. As a result, the yield of purified gallium can be improved and the purification efficiency can be improved. Therefore, the gallium raw material produced from the zinc smelting process, the crude gallium recovered from the compound semiconductor scrap, and further the gallium refining from the gallium raw material having a high impurity content generated from the high-purity gallium refining process can be greatly contributed. .
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of an apparatus for carrying out the method of the present invention.
FIG. 2 is a schematic plan view of an electrolytic cell portion of the apparatus of FIG.
[Explanation of symbols]
1 Electrolytic solution
2 Electrolysis tank
3 Gallium liquid raw material
4 Anode chamber
5 Cathode chamber
6 Cylindrical container
7 Magnet rotor
8 Suction pipe
9 Conductive rod
10 Metal terminal
11 Cathode plate
12 Partition plate
15 Scum gathered at the center of the surface of the gallium liquid raw material
17 Purified gallium outlet
20 Auxiliary electrolytic cell
21 Circulation circuit
24 Intermediate tank
25 Pipeline connecting suction pipe and intermediate tank
26 Filter
30 Heater
37 Raw material supply tube

Claims

In the gallium electrolytic purification method in which purified gallium is deposited in the electrolyte using the gallium raw material liquid as the anode, the scum generated on the anode surface is sucked out of the electrolytic cell together with a part of the electrolyte, and the electrolysis is completed. The operation of replenishing the anode gallium raw material liquid, and circulating the electrolytic solution in the electrolytic collection tank installed outside the electrolytic tank, and depositing gallium in the electrolytic solution on the cathode of the electrolytic collection tank A method of electrolytic purification of gallium, characterized by performing an operation of causing

In a gallium electrolytic purification method in which gallium raw material liquid is used as an anode and purified gallium is deposited in an electrolytic solution in a cathode, a centrifugal force is applied to the gallium raw material liquid of the anode by a magnetic field, and An operation of sucking out the electrolytic cell together with a part of the scum, an operation of separating the scum sucked out of the electrolytic cell and the electrolytic solution into the electrolytic cell after separating the scum with a filter, An operation for replenishing the gallium raw material liquid in the anode, and an operation for circulating the electrolytic solution in an electrolytic collection tank installed outside the electrolytic tank and depositing gallium in the electrolytic solution on the cathode of the electrolytic collection tank A method for electrolytic purification of gallium, characterized in that

Supplying the electrolytic solution passed through the electrolytic collection tank to the intermediate tank, and supplying the scum sucked out of the electrolytic tank and the electrolytic solution to the intermediate tank, and then supplying the scum from the intermediate tank to the filter. The method for electrolytic purification of gallium according to claim 2 .

A gallium having an anode chamber containing a gallium raw material liquid as an anode and a cathode chamber for collecting purified gallium deposited on the cathode, and containing an electrolyte so as to flow between the anode chamber and the cathode chamber In the electrolysis apparatus, the anode chamber is configured in a cylindrical container, a magnet rotor is installed below the outer side of the cylindrical container, a suction pipe is disposed in the center of the cylindrical container, and the electrolysis apparatus An auxiliary electrolytic cell having an insoluble anode and a cathode is provided outside the tank, a circuit for circulating the electrolytic solution between the electrolyzer and the auxiliary electrolytic cell is provided, an intermediate tank is further installed in the circulating circuit, and the suction pipe Is connected to the intermediate tank, and a filter is interposed in a pipe line extending from the intermediate tank to the electrolyzer.

The gallium electrolytic purification apparatus according to claim 4 , wherein the intermediate tank includes a heater.