IT202000029552A1 - ELECTROLYTIC RECOVERY OF LEAD FROM ALKALINE SOLUTIONS INCLUDING SOLUBLE SILICATE SOLUTIONS RESULTING FROM LEADED GLASS TREATMENT - Google Patents
ELECTROLYTIC RECOVERY OF LEAD FROM ALKALINE SOLUTIONS INCLUDING SOLUBLE SILICATE SOLUTIONS RESULTING FROM LEADED GLASS TREATMENT Download PDFInfo
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- IT202000029552A1 IT202000029552A1 IT102020000029552A IT202000029552A IT202000029552A1 IT 202000029552 A1 IT202000029552 A1 IT 202000029552A1 IT 102020000029552 A IT102020000029552 A IT 102020000029552A IT 202000029552 A IT202000029552 A IT 202000029552A IT 202000029552 A1 IT202000029552 A1 IT 202000029552A1
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- Prior art keywords
- lead
- recovery
- alkaline solutions
- electrolytic cells
- cathode material
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- 238000011084 recovery Methods 0.000 title claims description 14
- 239000012670 alkaline solution Substances 0.000 title claims description 13
- 239000000243 solution Substances 0.000 title description 14
- 238000011282 treatment Methods 0.000 title description 10
- 239000011521 glass Substances 0.000 title description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title 1
- 239000001257 hydrogen Substances 0.000 claims description 17
- 229910052739 hydrogen Inorganic materials 0.000 claims description 17
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 15
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 11
- 229910052725 zinc Inorganic materials 0.000 claims description 11
- 239000011701 zinc Substances 0.000 claims description 11
- 239000010406 cathode material Substances 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 5
- 229910000831 Steel Inorganic materials 0.000 claims description 5
- 229910052793 cadmium Inorganic materials 0.000 claims description 5
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 claims description 5
- 229910052738 indium Inorganic materials 0.000 claims description 5
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 5
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- 239000011777 magnesium Substances 0.000 claims description 5
- 150000002739 metals Chemical class 0.000 claims description 5
- 239000010959 steel Substances 0.000 claims description 5
- 239000010405 anode material Substances 0.000 claims description 2
- 238000007254 oxidation reaction Methods 0.000 claims description 2
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims 2
- 239000000463 material Substances 0.000 description 13
- 150000002431 hydrogen Chemical class 0.000 description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 238000005868 electrolysis reaction Methods 0.000 description 7
- YADSGOSSYOOKMP-UHFFFAOYSA-N dioxolead Chemical compound O=[Pb]=O YADSGOSSYOOKMP-UHFFFAOYSA-N 0.000 description 6
- 229910001220 stainless steel Inorganic materials 0.000 description 6
- 239000005355 lead glass Substances 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 239000010935 stainless steel Substances 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 4
- 239000011651 chromium Substances 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 229910021653 sulphate ion Inorganic materials 0.000 description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 150000002978 peroxides Chemical class 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 2
- 229910001335 Galvanized steel Inorganic materials 0.000 description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 229910052733 gallium Inorganic materials 0.000 description 2
- 239000008397 galvanized steel Substances 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 238000002386 leaching Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- 239000010948 rhodium Substances 0.000 description 2
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 2
- 229910052707 ruthenium Inorganic materials 0.000 description 2
- 150000004760 silicates Chemical class 0.000 description 2
- 229910052716 thallium Inorganic materials 0.000 description 2
- BKVIYDNLLOSFOA-UHFFFAOYSA-N thallium Chemical compound [Tl] BKVIYDNLLOSFOA-UHFFFAOYSA-N 0.000 description 2
- 150000003568 thioethers Chemical class 0.000 description 2
- 239000010963 304 stainless steel Substances 0.000 description 1
- 206010011906 Death Diseases 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- WBLCSWMHSXNOPF-UHFFFAOYSA-N [Na].[Pb] Chemical compound [Na].[Pb] WBLCSWMHSXNOPF-UHFFFAOYSA-N 0.000 description 1
- WOIHABYNKOEWFG-UHFFFAOYSA-N [Sr].[Ba] Chemical compound [Sr].[Ba] WOIHABYNKOEWFG-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229910001854 alkali hydroxide Inorganic materials 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- -1 hydrogen ions Chemical class 0.000 description 1
- 230000002427 irreversible effect Effects 0.000 description 1
- 239000011133 lead Substances 0.000 description 1
- 229910000464 lead oxide Inorganic materials 0.000 description 1
- HTUMBQDCCIXGCV-UHFFFAOYSA-N lead oxide Chemical compound [O-2].[Pb+2] HTUMBQDCCIXGCV-UHFFFAOYSA-N 0.000 description 1
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000009853 pyrometallurgy Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 239000011135 tin Substances 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
- C25C1/18—Electrolytic production, recovery or refining of metals by electrolysis of solutions of lead
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
- C25C7/02—Electrodes; Connections thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Description
DESCRIZIONE dell?invenzione avente per TITOLO: DESCRIPTION of the invention with TITLE:
Recupero elettrolitico di piombo da soluzioni alcaline comprese le soluzioni di silicati solubili derivanti dal trattamento di vetro al piombo Electrolytic recovery of lead from alkaline solutions including soluble silicate solutions resulting from the treatment of lead glass
Campo di applicazione tecnica Technical scope
Celle elettrolitiche speciali per il recupero massivo di metalli pesanti al loro stato metallico da soluzioni alcaline, in particolare di celle elettrolitiche speciali per il recupero massivo del piombo al suo stato metallico da soluzioni alcaline. Special electrolytic cells for the massive recovery of heavy metals in their metallic state from alkaline solutions, in particular special electrolytic cells for the massive recovery of lead in their metallic state from alkaline solutions.
Stato dell?arte State of art
Esistono molti processi che, mediante trattamenti in ambiente alcalino, solubilizzano sali di piombo da recuperare, in seguito, sottoforma di metallo mediante elettrolisi. Una fonte importante di soluzioni alcaline contenente sali di piombo sono quelle derivanti dal trattamento del vetro al piombo presenti nei vecchi televisori a tubo catodico. Un?altra sorgente, spesso sottovalutata, di sali di piombo sono i residui dell?estrazione dello zinco, come solfato, dai minerali che li contengono come solfuri. In questi processi, generalmente, i minerali sono arrostiti in aria per convertire i solfuri in ossidi o solfati. Segue una lisciviazione acida con solforico al fine di portare in soluzione lo zinco come solfato. Questa operazione arrostimento-lisciviazione viene eseguita numerose volte al fine di massimizzare l?estrazione dello zinco. Il materiale risultante da questo processo ? ora arricchito in piombo sottoforma di solfato per cui ? possibile solubilizzare il piombo sottoforma di piombito per trattamento con idrossidi alcalini. Normalmente, invece, questi residui sono trattati in processi tradizionali pirometallurgici per il recupero del piombo. Per quanto riguarda il trattamento del vetro al piombo, in moltissime nazioni si attua da tempo la raccolta differenziata delle apparecchiature elettriche ed elettroniche a fine vita, denominate in Italia RAEE ("Rifiuti da Apparecchiature Elettriche ed Elettroniche") o internazionalmente WEEE ( Waste of Electric and Electronic Equipment). Aziende specializzate sottopongono queste apparecchiature a numerosi trattamenti al fine di recuperare materie prime ? seconde come i circuiti e le schede elettroniche, la bobina in rame, materiali plastici, cavi elettrici. La parte in vetro ? separata ricavando due tipologie di vetro: lo schermo e il cono. Lo schermo ? realizzato con vetro bario-stronzio che, dopo essere stato ripulito dai ?fosfori?, materiali che diventano luminescenti se colpiti dai raggi catodici formano l?immagine, viene riciclato per diverse applicazioni, ad esempio nell?industria ceramica. Il vetro cono, costituito da vetro ad alto contenuto di ossido di piombo, fino al 22%, trova applicazioni molto limitate e, generalmente, ? messo in discarica con un potenziale elevato impatto ambientale oltre alla perdita irreversibile di materiali di valore, piombo in particolare. Molti sono i brevetti e pubblicazioni inerenti il trattamento del vetro al piombo con lo scopo principale se non unico di recuperare il piombo. Secondo quanto riportato nei brevetti, il piombo ? recuperato sempre mediante elettrolisi diretta dalla soluzione di silicati e, a volte, l?eliminazione totale del piombo da queste soluzioni ? attuato anche mediante una successiva reazione di cementazione con zinco metallico. In alcuni brevetti si rivendica anche la periodica inversione di polarit? degli elettrodi al fine di facilitare il distacco del piombo depositato al catodo. Tutti i brevetti rivendicano l?utilizzo di materiali elettrodici non idonei, spesso del medesimo materiale, acciaio inossidabile, per la realizzazione degli elettrodi. E? noto, per?, che su questo materiale il piombo che si scarica forma depositi incoerenti e spugnosi che inglobano moltissima soluzione e idrogeno rendendo molto difficoltosa l?operazione di recupero del piombo. Il rendimento di corrente risulta, inoltre, inevitabilmente molto basso a causa della concorrente e concomitante reazione di scarica dell?idrogeno. La causa di questo fenomeno ? dovuta al fatto che la scarica dell?idrogeno in condizioni normali ? termodinamicamente favorita rispetto a quella del piombo. Operando l?elettrolisi, ad esempio, di una soluzione alcalina di silicati derivante dal trattamento del vetro al piombo, la concentrazione iniziale del piombo ammonta ad almeno 0,25 moli/kg mentre il pH della soluzione si attesta intorno al valore di 13. Ci? significa che la concentrazione degli idrogenioni ? di 10<-13 >g moli/litro. In queste condizioni, inizialmente, secondo la legge di Nernst, la scarica catodica favorita diventa quella del piombo essendo questo ione presente con una concentrazione di 13 ordini di grandezza pi? elevata. Con il procedere della scarica, la soluzione si depaupera dagli ioni piombo e comincia a diventare prevalente quella dell?idrogeno con conseguente abbassamento significativo del rendimento di corrente. Il problema ?, inoltre, esaltato dall?utilizzo dell?acciaio inox come materiale elettrodico che presenta una bassa sovratensione per la scarica dell?idrogeno. In questo processo, pertanto, la scelta soprattutto dei materiali con cui realizzare il catodo riveste una decisiva importanza sia per la morfologia del piombo depositato sia per il rendimento di corrente. Al catodo, infatti, sono possibili due reazioni competitive: quella di scarico di idrogeno e quella di riduzione degli ioni piombo a dare piombo metallico. La prima risulta termodinamicamente favorita e per limitarla/impedirla occorre che il materiale catodico presenti una elevata sovratensione alla scarica dell?idrogeno. Sono, di seguito, elencati, in termini di sovratensione decrescente per la scarica dell?idrogeno, alcuni metalli: tallio, mercurio, gallio, indio, magnesio, piombo, cadmio, zinco, argento, stagno, germanio, bismuto, antimonio, rame, cromo, ferro, cobalto, nichel, rutenio, rodio, platino. I costituenti dell?acciaio inox AISI 304 sono: cromo 18-20%, nichel 8 -11 %, ferro a bilancio, quelli presenti nell?acciaio inox AISI 316 sono: cromo 16-18%, nichel 11-14, molibdeno 2-3%, ferro a bilancio. Nelle celle elettrolitiche descritte sono utilizzati acciai inox in cui sono presenti proprio tre elementi, Fe, Cr, Ni che presentano la pi? bassa sovratensione di scarica dell?idrogeno, a parte i metalli nobili come rutenio, rodio e platino. Questo comporta, in base alla scala della sovratensione di scarica dell?idrogeno, un basso rendimento di corrente nell?elettrodeposizione del piombo e la sua formazione allo stato spugnoso in quanto ingloba idrogeno. Per quanto concerne il materiale costituente l?anodo viene spesso impiegato il medesimo acciaio inox utilizzato per i catodi. La scelta risulta obbligata in quanto in molti brevetti si rivendicano processi di elettrolisi che prevedono l?inversione della polarit? agli elettrodi al fine di favore il distacco del piombo depositatosi sui catodi. La scelta dell?acciaio inossidabile come anodo comporta la formazione di biossido di piombo e di perossidi in soluzione che rendono impura la soluzione di silicati in fase di elettrolisi. Quanto descritto per il recupero del piombo dalle soluzioni alcaline di silicati vale anche per il recupero di questo metallo per elettrolisi da soluzioni di piombiti di ioni alcalini derivanti dal trattamento dalle masse residue di lisciviazione nei processi di produzione dello zinco mediante elettrolisi di soluzioni di solfato di zinco. There are many processes which, by means of treatments in an alkaline environment, solubilize lead salts to be subsequently recovered in the form of metal by electrolysis. An important source of alkaline solutions containing lead salts are those deriving from the treatment of lead glass present in old CRT televisions. Another source, often underestimated, of lead salts are the residues of the extraction of zinc, as sulphate, from minerals that contain them as sulphides. In these processes, minerals are typically roasted in air to convert the sulfides into oxides or sulfates. An acid leaching with sulfuric acid follows in order to bring the zinc into solution as sulphate. This roast-leach operation is performed numerous times in order to maximize zinc extraction. The material resulting from this process? now enriched in lead in the form of sulphate for which ? It is possible to solubilize lead in the form of lead by treatment with alkali hydroxides. Normally, however, these residues are treated in traditional pyrometallurgical processes for the recovery of lead. As far as the treatment of lead glass is concerned, separate collection of end-of-life electrical and electronic equipment has been implemented in many countries for some time, known in Italy as RAEE ("Refuse from Electrical and Electronic Equipment") or internationally as WEEE (Waste of Electric and Electronic Equipment). Specialized companies subject these equipment to numerous treatments in order to recover raw materials? second such as circuits and electronic boards, the copper coil, plastic materials, electric cables. The glass part? separated by obtaining two types of glass: the screen and the cone. The screen ? made with barium-strontium glass which, after being cleaned of the "phosphors", materials that become luminescent when hit by cathode rays form the image, is recycled for various applications, for example in the ceramic industry. Cone glass, made up of glass with a high lead oxide content, up to 22%, finds very limited applications and is generally ? landfilled with a potential high environmental impact in addition to the irreversible loss of valuable materials, lead in particular. There are many patents and publications concerning the treatment of lead glass with the main purpose, if not the only one, of recovering the lead. According to what is reported in the patents, the lead ? always recovered by direct electrolysis from the silicate solution and, sometimes, the total elimination of lead from these solutions? also carried out by means of a subsequent cementation reaction with metallic zinc. Some patents also claim the periodic reversal of polarity? of the electrodes in order to facilitate the detachment of the lead deposited at the cathode. All patents claim the use of unsuitable electrode materials, often of the same material, stainless steel, for making the electrodes. AND? However, it is known that on this material the discharged lead forms incoherent and spongy deposits which absorb a great deal of solution and hydrogen, making the lead recovery operation very difficult. Furthermore, the current efficiency is inevitably very low due to the concurrent and concomitant hydrogen discharge reaction. The cause of this phenomenon? due to the fact that the discharge of? hydrogen under normal conditions ? thermodynamically favored over that of lead. By operating the electrolysis, for example, of an alkaline solution of silicates deriving from the treatment of lead glass, the initial concentration of lead amounts to at least 0.25 moles/kg while the pH of the solution is around the value of 13. There ? means that the concentration of hydrogen ions ? of 10<-13 >g moles/litre. Under these conditions, initially, according to Nernst's law, the favored cathodic discharge becomes that of lead, this ion being present with a concentration of 13 orders of magnitude higher than that of lead. elevated. As the discharge proceeds, the solution is depleted of lead ions and that of hydrogen begins to prevail with a consequent significant lowering of the current efficiency. The problem is further enhanced by the use of stainless steel as the electrode material which has a low overvoltage due to the hydrogen discharge. In this process, therefore, above all the choice of the materials with which to make the cathode is of decisive importance both for the morphology of the deposited lead and for the current efficiency. At the cathode, in fact, two competitive reactions are possible: that of hydrogen discharge and that of reduction of the lead ions to give metallic lead. The former is thermodynamically favored and to limit/prevent it, the cathode material must have a high overvoltage upon hydrogen discharge. Some metals are listed below in terms of decreasing overvoltage for the hydrogen discharge: thallium, mercury, gallium, indium, magnesium, lead, cadmium, zinc, silver, tin, germanium, bismuth, antimony, copper, chromium, iron, cobalt, nickel, ruthenium, rhodium, platinum. The constituents of AISI 304 stainless steel are: chromium 18-20%, nickel 8 -11%, iron on balance, those present in stainless steel AISI 316 are: chromium 16-18%, nickel 11-14, molybdenum 2- 3%, budget iron. In the electrolytic cells described, stainless steels are used in which there are precisely three elements, Fe, Cr, Ni which present the most? low hydrogen discharge overvoltage, apart from noble metals such as ruthenium, rhodium and platinum. On the basis of the hydrogen discharge overvoltage scale, this entails a low current efficiency in the electrodeposition of lead and its formation in a spongy state as it incorporates hydrogen. As regards the material constituting the anode, the same stainless steel used for the cathodes is often used. The choice is obligatory as many patents claim electrolysis processes which provide for the inversion of the polarity? to the electrodes in order to favor the detachment of the lead deposited on the cathodes. The choice of stainless steel as anode involves the formation of lead dioxide and peroxides in the solution which make the silicate solution impure in the electrolysis phase. What has been described for the recovery of lead from alkaline solutions of silicates also applies to the recovery of this metal by electrolysis from lead solutions of alkaline ions deriving from the treatment of the residual masses of leaching in the zinc production processes by electrolysis of solutions of sulphate of zinc.
Descrizione tecnica Technical description
Oggetto di questo brevetto sono le celle elettrolitiche realizzate utilizzando particolari materiali per la realizzazione dei catodi e degli anodi. Le caratteristiche salienti di queste celle risiedono nella scelta di materiali elettrodici. Quelli catodici presentano un?elevata sovratensione di scarica dell?idrogeno, ovvero che hanno un valore di log10 i0 (A/cm<2>) compreso fra -7 e -13, dove i0 ? la densit? di corrente di scambio per la reazione di ossidazione dell?idrogeno a 25?C, mentre quelli anodici non favoriscono la formazione di biossido di piombo e di perossidi. A tale scopo come catodi, pur presentando la pi? alta sovratensione per la scarica dell?idrogeno, sono stati scartati a priori, per la loro tossicit?, il tallio e il mercurio mentre il gallio non ? idoneo per questo utilizzo a causa del suo basso punto di fusione. Si sono dimostrati molto efficaci, invece, i catodi ricavati per deposizione di sottili strati di indio o di cadmio su acciaio. Altrettanto efficaci sono stati i catodi realizzati con lastre di zinco o di acciaio zincato, e quelli ricavati con lastre di magnesio o di piombo. Impiegando questi materiali per la realizzazione dei catodi, non ? possibile attuare l?inversione della polarit? per favorire il distacco del piombo pena la distruzione del materiale catodico. In funzione della natura dei materiali utilizzati al catodo si avranno depositi di piombo incoerenti sottoforma di polvere sottile di colore nero, ad esempio operando con catodo in magnesio, oppure depositi coerenti e ben formati, come nel caso del catodo in piombo. In ogni caso, indipendentemente dal materiale adottato come catodo, si pu? operare con densit? di corrente molto elevata, fino a 1.000 A/m<2 >e con elevata efficienza di corrente. Si realizzano, pertanto, risparmi sia dal punto di vista energetico che nei costi di realizzazione delle celle elettrolitiche. ? stato inoltre sorprendentemente scoperto che utilizzando il nichel come materiale anodico, non si verifica la formazione di biossido di piombo e la generazione di perossidi in soluzione. Le celle oggetto di questo brevetto sono, pertanto, realizzate con anodi in nichel puro o acciaio nichelato e catodi con uno dei seguenti materiali: magnesio, piombo, zinco, acciaio zincato, acciaio ricoperto con indio o con cadmio. The subject of this patent are the electrolytic cells made using particular materials for making the cathodes and anodes. The salient features of these cells lie in the choice of electrode materials. The cathodic ones have a high hydrogen discharge overvoltage, i.e. they have a value of log10 i0 (A/cm<2>) between -7 and -13, where i0 ? the density? of exchange current for the hydrogen oxidation reaction at 25°C, while the anodic ones do not favor the formation of lead dioxide and peroxides. For this purpose, as cathodes, while presenting the pi? high overvoltage for the discharge of? hydrogen, have been rejected a priori, for their toxicity?, the thallium and the mercury while the gallium is not? suitable for this use due to its low melting point. On the other hand, the cathodes obtained by depositing thin layers of indium or cadmium on steel have proved to be very effective. Equally effective were the cathodes made with zinc or galvanized steel plates, and those made with magnesium or lead plates. Employing these materials for the realization of the cathodes, isn't it? is it possible to implement the? inversion of the polarity? to favor the detachment of the lead under penalty of destruction of the cathode material. Depending on the nature of the materials used for the cathode, there will be incoherent lead deposits in the form of a fine black powder, for example when working with a magnesium cathode, or coherent and well-formed deposits, as in the case of the lead cathode. In any case, regardless of the material adopted as the cathode, you can? operate with density? very high current, up to 1,000 A/m<2 >and with high current efficiency. Therefore, savings are achieved both from an energy point of view and in the manufacturing costs of the electrolytic cells. ? it has also been surprisingly discovered that by using nickel as an anode material, the formation of lead dioxide and the generation of peroxides in solution do not occur. The cells object of this patent are, therefore, made with anodes in pure nickel or nickel-plated steel and cathodes with one of the following materials: magnesium, lead, zinc, galvanized steel, steel covered with indium or with cadmium.
Esempio 1. Example 1.
Sono stati trattati 75 kg di silicato di sodio contenente il 3% di piombo sotto forma di piombito di sodio in una cella avente come catodi 3 lastre di piombo dolce 2 lastre di acciaio nichelato con una nichelatura di 30 micron. ? stata applicata una densit? di corrente pari a 500 A/m<2 >per 6 ore e la temperatura ? stata mantenuta a 70?C, alla fine delle quali la concentrazione di piombo all?interno della soluzione ? scesa a 100 ppm. Il rendimento di corrente calcolato a fine operazione ? del 72%. 75 kg of sodium silicate containing 3% of lead in the form of sodium lead was treated in a cell having as cathodes 3 plates of soft lead and 2 plates of nickel-plated steel with a nickel plating of 30 microns. ? was applied a density? of current equal to 500 A/m<2 > for 6 hours and the temperature? been maintained at 70?C, at the end of which the concentration of lead inside the solution? dropped to 100ppm. The current yield calculated at the end of the operation? by 72%.
Claims (6)
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| IT102020000029552A IT202000029552A1 (en) | 2020-12-02 | 2020-12-02 | ELECTROLYTIC RECOVERY OF LEAD FROM ALKALINE SOLUTIONS INCLUDING SOLUBLE SILICATE SOLUTIONS RESULTING FROM LEADED GLASS TREATMENT |
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| IT102020000029552A IT202000029552A1 (en) | 2020-12-02 | 2020-12-02 | ELECTROLYTIC RECOVERY OF LEAD FROM ALKALINE SOLUTIONS INCLUDING SOLUBLE SILICATE SOLUTIONS RESULTING FROM LEADED GLASS TREATMENT |
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101748277A (en) * | 2008-12-03 | 2010-06-23 | 江苏航虹电源有限公司 | Method for recovering lead from waste lead acid batteries |
| CN101831668B (en) * | 2010-05-21 | 2012-02-22 | 北京化工大学 | Clean wet-method solid-liquid two-phase electroreduction lead recovery method |
| CN108570692A (en) * | 2017-03-09 | 2018-09-25 | 西安优庆商贸有限公司 | A method of by the leaded converting waste material containing lead battery be metallic lead |
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- 2020-12-02 IT IT102020000029552A patent/IT202000029552A1/en unknown
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101748277A (en) * | 2008-12-03 | 2010-06-23 | 江苏航虹电源有限公司 | Method for recovering lead from waste lead acid batteries |
| CN101831668B (en) * | 2010-05-21 | 2012-02-22 | 北京化工大学 | Clean wet-method solid-liquid two-phase electroreduction lead recovery method |
| CN108570692A (en) * | 2017-03-09 | 2018-09-25 | 西安优庆商贸有限公司 | A method of by the leaded converting waste material containing lead battery be metallic lead |
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