Evaluation of precipitation processes for the removal of iron from chloride-based copper and nickel leach solutions

Masambi, Saviour (2015-12)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: A process route is being developed to recover nickel and copper from chloride leach solutions contaminated with iron. The concentrations of nickel and copper are approximately 3 g/L each, while that of iron is about 45 g/L. Iron contamination causes problems in processes typically used for the recovery of nickel and copper from leach solutions, such as solvent extraction or sulphide precipitation. This study focused on the removal of iron from the chloride-based leach solution. Iron is commonly removed from hydrometallurgical solutions by the process of precipitation. In the leach solution under investigation, iron mainly exists as iron(II) chloride. Iron(II) generally precipitates at pH above 7 while iron(III) can be precipitated at pH above 0. In this study, it was desired to oxidize iron(II) to iron(III) using oxygen gas at a temperature below 100oC and to subsequently precipitate iron(III). It was sought to produce an environmentally friendly precipitate, with minimal nickel and copper co-precipitation and easily separate the solids from the liquid. The effect of hydrochloric acid and copper concentration on the rate of iron(II) oxidation were experimentally determined. Several concentrations of hydrochloric acid, ranging from about 0.7 M to 6.4 M, were investigated while the copper concentrations investigated were 0.3 g/L and 3 g/L. The effects of temperature (40oC, 60oC, 80oC and 90oC), pH (0, 1, 2 and 3) and 30 g/L seeding on the quality and extent of iron removal were experimentally determined. The conventional hematite precipitation process was compared to the iron phosphate process in terms of iron removal, nickel and copper co-precipitation, and solid-liquid separation. The experiments were conducted in a 1.6 L glass reactor using synthetic as well as plant solutions. Synthetic solutions contained about 45 g/L iron, 3 g/L nickel and copper. Plant solutions contained significantly higher iron and nickel, with traces of copper. The concentrations of iron and nickel in plant solutions were approximately 120 g/L and 12 g/L respectively. The rate and extent of oxidation of iron(II) , using synthetic solutions, increased with both acid and copper concentrations. Experimental data and equilibrium calculations were used to prove that the mole ratio of associated acid to iron needed to be greater than or equal to 1 for rapid oxidation of iron(II) to occur. It was experimentally shown that oxidation in the presence of 3 g/L copper concentration yielded higher iron(III) compared to oxidation in the presence of 0.3 g/L copper concentration under uniform conditions. Iron precipitation from synthetic solutions was complete at all pH points investigated (0, 1, 2, 3) in both iron phosphate and hematite precipitation processes. The co-precipitation of nickel and copper increased with pH for both precipitation processes. The co-precipitation of nickel and copper in the iron phosphate process increased with an increase in temperature from 40oC while the co-precipitation of nickel and copper increased with reduction in temperature from 80oC in the hematite precipitation process. Seeded iron phosphate precipitation at pH 1 and 40oC resulted in over 99% iron removal with averages of 5% and 11% nickel and copper co-precipitation respectively. Increasing the pH to 3 resulted in complete iron removal at the expense of over 50% losses in nickel and copper. Seeded hematite precipitation at pH 1 and 80oC yielded over 99% iron removal with averages of 6.5% nickel and 7% copper losses. Upon increasing the pH to 3, nickel and copper losses were above 35%. The iron phosphate precipitation was complete within 30 – 60 minutes while hematite precipitation was complete after 60 – 120 minutes. All seeded precipitation experiments produced easily filterable precipitates. Attempts to precipitate unseeded hematite at 80oC and pH 1 resulted in higher nickel and copper losses (about 16% and 27% respectively), with the precipitates practically impossible to filter. The unseeded iron phosphate precipitates produced at 40oC and pH 1 were filterable however relatively higher losses of nickel and copper were observed (about 11% and 22% respectively). Settling experiments showed that iron phosphate precipitates completely settled within 26 minutes. Hematite precipitates did not settle after 8 h. Plant solutions were tested to validate the direct applicability of the results obtained using synthetic solutions. It was observed that complete oxidation was achieved after 180 minutes. Iron phosphate precipitation at pH 1 and 40oC achieved complete iron removal after 60 minutes and nickel losses of approximately 7.8% after 120 minutes. Hematite precipitation at pH 1 and 80oC resulted in complete iron removal after 60 min and nickel co-precipitation of 12% after 120 minutes.

AFRIKAANSE OPSOMMING: ʼn Prosesroete word tans ontwikkel om nikkel en koper te herwin vanuit chloried logingsoplossings wat met yster kontamineer is. Die konsentrasies van nikkel en koper is ongeveer 3 g/L elk, terwyl die konsentrasie van yster ongeveer 45 g/L is. Yster kontaminasie veroorsaak probleme in prosesse wat tipies gebruik word vir die herwinning van nikkel en koper van logingsoplossings, soos byvoorbeeld vloeistof-vloeistof ekstraksie of sulfied presipitasie. Hierdie studie het op die verwydering van yster vanuit die chloried logingsoplossing gefokus. Yster word algemeen vanuit hidrometallurgiese oplossings verwyder met die proses van presipitasie. In die logingsoplossing relevant tot hierdie studie bestaan die yster hoofsaaklik as yster(II)chloried. Yster(II) sal gewoonlik by pH waardes bo 7 presipiteer, terwyl yster(III) by pH waardes groter as 0 presipiteer kan word. Die gewenste roete in hierdie studie was om die yster(II) te oksideer na yster(III) deur van suurstofgas by ʼn temperatuur onder 100°C gebruik te maak, en om daarna yster(III) te presipiteer. Die presipitaat moes omgewingsvriendelik wees met minimale nikkel en koper kopresipitasie, en moes maklik van die oplossing geskei kon word. Die effek van soutsuur en koper konsentrasie op die tempo van yster(II) oksidasie is eksperimenteel bepaal. Verskeie konsentrasies soutsuur in die gebied van 0.7 M tot 6.4 M is ondersoek, terwyl koper konsentrasies van 0.3 g/L en 3 g/L ondersoek is. Die effekte van temperatuur (40°C, 60°C, 80°C en 90°C), pH (0, 1, 2 en 3), en 30 g/L saad byvoeging op die kwaliteit en mate van yster verwydering is eksperimenteel bepaal. Die konvensionele hematiet presipitasie proses is met die ysterfosfaat proses vergelyk in terme van ysterverwydering, nikkel en koper kopresipitasie, en vastestof-vloeistof skeiding. Die eksperimente is in ʼn 1.6 L glas reaktor met sintetiese sowel as aanleg logingsoplossings uitgevoer. Die sintetiese oplossing het ongeveer 45 g/L yster en 3 g/L nikkel en koper bevat. Aanleg oplossing het beduidend hoër konsentrasies yster en nikkel bevat, met spore van koper teenwoordig. Die konsentrasies van yster en nikkel in die aanleg oplossing was ongeveer 120 g/L en 12 g/L, onderskeidelik. Die tempo en mate van oksidasie van yster(II) in sintetiese oplossing het toegeneem met beide suur en koper konsentrasies. Eksperimentele data en ewewigsberekeninge is gebruik om te bewys dat die molêre verhouding van geassosieerde suur tot yster groter of gelyk aan een moet wees om vinnige oksidasie van yster(II) te laat plaasvind. Dit is eksperimenteel bewys dat, onder soortgelyke toestande, oksidasie in die teenwoordigheid van 3 g/L koper konsentrasie hoër yster(III) gelewer het as oksidasie in die teenwoordigheid van 0.3 g/L koper konsentrasie. Yster presipitasie vanuit sintetiese oplossings was volledig by alle pH waardes wat ondersoek is (0, 1, 2, 3) in beide die ysterfosfaat en die hematiet presipitasie prosesse. Die kopresipitasie van nikkel en koper het toegeneem met pH vir beide presipitasie prosesse. Die kopresipitasie van nikkel en koper in die ysterfosfaat proses het toegeneem met ʼn toename in temperatuur vanaf 40°C, terwyl die kopresipitasie van nikkel en koper toegeneem het met ʼn verlaging in temperatuur vanaf 80°C in die hematiet proses. Ysterfosfaat presipitasie met sade wat by pH1 en 40°C uitgevoer is, het tot meer as 99% yster verwydering gelei, met gemiddelde nikkel en koper kopresipitasie van 5% en 11%, onderskeidelik. Volledige yster verwydering is behaal indien die pH tot 3 verhoog is, maar die nikkel en koper verliese het terselfdertyd tot meer as 50% verhoog. Hematiet presipitasie met sade by pH 1 en 80°C het meer as 99% yster verwydering behaal, met gemiddelde nikkel en koper verliese van 6.5% en 7%, onderskeidelik. Die nikkel en koper verliese het tot meer as 35% gestyg met ʼn pH toename na 3. Die ysterfosfaat presipitasie is binne 30 – 60 minute voltooi, terwyl hematiet 60 – 120 minute geneem het om voltooiing te bereik. Alle presipitasie eksperimente wat met sade uitgevoer is, het maklik filtreerbare presipitate produseer. Pogings om hematiet sonder sade te presipiteer by 80°C en pH 1 het aanleiding gegee tot hoër nikkel en koper verliese (ongeveer 16% en 27%, onderskeidelik) sowel as presipitaat wat basies onmoontlik was om te filtreer. Die ysterfosfaat presipitaat wat sonder sade by 40°C en pH 1 produseer is was filtreerbaar maar relatiewe hoër verliese van nikkel en koper is waargeneem (ongeveer 11% en 22%, onderskeidelik). Uitsakking eksperimente het getoon dat ysterfosfaat presipitate volledig uitsak binne 26 minute. Hematiet presipitate het nie uitgesak na ag ure nie. Aanleg oplossings is getoets om die toepaslikheid van die resultate wat met sintetiese oplossings verkry is te bevestig. Volledige oksidasie is na 180 minute behaal. Ysterfosfaat presipitasie by pH 1 en 40°C het volledige yster verwydering na 60 minute behaal met nikkel verliese van ongeveer 7.8% na 120 minute. Hematiet presipitasie by pH 1 en 80°C het volledige yster verwydering na 60 minute behaal met nikkel kopresipitasie van 12% na 120 minute.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97782
This item appears in the following collections: