Studies on the Recovery of Secondary Antimony Compounds from Waste
Doktorsavhandling, 2017

The global supply of antimony is dominated by one country which has led the European Union to classify antimony as a critical raw material. Other than the rare-earth elements antimony has the highest supply risk. Therefore, a feasibility study on the recycling of antimony and antimony compounds is of great importance. This research focuses on two types of antimony containing wastes: (1) metal oxide varistors (MOVs) and (2) municipal solid waste incineration (MSWI) fly ash to determine if it is possible to recover secondary antimony. Recovery of antimony is highlighted because it is a critical element and the known natural resources are rapidly becoming depleted. The MOVs contain a significant amount of antimony but have minimal waste volumes. Characterization of the MOV determined the microstructure of the MOV contained the three major phases (1) the zinc rich phase dominated by ZnO grains, (2) the antimony rich phase containing Zn2.33Sb0.67O4, Zn7Sb2O12, and Zn2Bi3Sb3O14 compounds, and (3) the bismuth rich phase made up of Bi2O3. To increase the antimony concentration, the MOV was pulverized and leached in a pre-treatment step. The pretreatment step removed the bulk ZnO grains from the MOV resulting in a zinc-sulfate leachate and antimony rich insoluble residue having a fivefold increase in antimony concentration. Removal of the minor metals such as cobalt, manganese, and nickel from the zinc sulfate leachate was done by activated cementation using Cu/Sb as activators and zinc dust as the reducing agent. It was determined for the MOV leachate system that the optimized cementations conditions for copper concentration, antimony concentration, zinc dust addition, temperature and pH were found to be 0.8 g·L-1 Sb, 0.4 g·L-1 Cu, T = 40 °C, 0.2 g·L-1 Zn addition in a solution of pH 5.0. A two-step batch cementation process resulted in 98 % removal of cobalt and 100 % removal of nickel making the purified zinc sulfate leachate suitable for zinc electrowinning. The antimony rich leach residue was subjected to heat treatment as well as carbothermal reduction in nitrogen atmosphere. Findings suggest that thermolysis of the MOV leaching residue and separation of antimony was not possible below 1000 °C. However, carbothermal reduction of the MOV leaching residue showed it was possible to separate antimony at temperatures between 700 – 825 °C by the decomposition of Zn7Sb2O12. In this process antimony oxide, Sb4O6(g), was separated from the MOV residue leaving zinc oxide and other metals including bismuth, cobalt, manganese, and nickel. The volatilized Sb4O6 can be recovered through condensation from the gaseous state. Two MSWI fly ash samples were used (1) untreated and (2) HALOSEP-treated fly ash to determine the amount of antimony which could be extracted from MSWI fly ash as a function of pH. The HALOgen SEParation (HALOSEP) process is used to remove water soluble salts such as NaCl, KCl, CaCl2, and MgCl2 and to alter the leaching properties of the fly ash with respect to metals such as antimony, lead, and zinc. Results showed that the maximum amount of antimony that could be extracted from the ashes was approximately 20 % using a pH 1 HCl solution with L/S of 20. Increasing the pH gave lower antimony yields. It was determined that very little of the antimony could be recovered or removed from the fly ash, which makes commercialization of such a process difficult. However, leaching did cause the concentration of antimony in the dry residue to increase due to dissolution of bulk minerals, which suggests a two-step leaching process could be preferable for antimony recovery.

Morphology

Thermolysis

Leaching

Municipal Solid Waste

Zinc

Metal Oxide Varistor

Cementation

Fly Ash

Recycling

Antimony

10:an
Opponent: Prof. Vadim Kessler, Sveriges Lantbruksuniversitet, Institutionen för molekylära vetenskaper, Uppsala Sweden

Författare

Toni Karlsson

Chalmers, Kemi och kemiteknik, Energi och material, Kärnkemi

Recycling Zinc from Metal Oxide Varistors Through Leaching and Cementation of Cobalt and Nickel

JOURNAL OF SUSTAINABLE METALLURGY,; Vol. 3(2017)p. 239-250

Artikel i vetenskaplig tidskrift

Investigations into high temperature separation of antimony from metal oxide varistors

Journal of Cleaner Production,; Vol. 162(2017)p. 474-483

Artikel i vetenskaplig tidskrift

T. Karlsson, Y. Colombus and B.-M. Steenari. “Investigation of the Kinetics and the Morphology of Cementation Products Formed During Purification of Zinc Sulfate Electrolyte.” Manuscript.

T. Gutknecht, C. Forsgren and B.-M. Steenari. “Recovery of Antimony: A laboratory study on the thermal decomposition and carbothermal reduction of Sb(III), Bi(III), Zn(II) oxides and antimony compounds from metal oxide varistors.” Accepted to Journal of Sustainable Metallurgy 11/2017.

T. Karlsson, H. Jilvero, Y. Colombus, L. Nordhag, E. Rasmussen, C. Forsgren, and B.-M. Steenari. “pH-Dependent Leaching of Sb, Pb, and Zn from MSWI Fly Ash Before and After an Acid Treatment.” Submitted to Waste Management 09/2017.

Det finns för närvarande över 7 miljarder människor på jorden av vilka cirka 3 miljarder människor i lever en urban livsstil. I dag genererar de 3 miljarder som bor i stadsområden i genomsnitt 1,2 kg/capita/dag (1,3 miljarder ton per år) av kommunalt fast avfall. Med den nuvarande mängd avfall som genereras måste vi tillsammans genomföra långsiktiga, hållbara åtgärder för att hantera dagens och framtidens avfall.

Denna forskning fokuserar på den mindre kända metalloiden, antimon och möjligheten att återvinna den från avfall. Två typer av avfall användes (1) metalloxidvaristorer (MOV), används som högspänningsskydd, innehåller en relativt stor mängd antimon i en liten avfallsfraktion och (2) flygaska från kommunalt förbränningsavfall som innehåller en relativt liten mängd antimon men av vilka stora mängder genereras årligen. Det globala utbudet av antimon domineras av ett land vilket har lett Europeiska unionen att klassificera antimon som ett kritiskt råmaterial. Bortsett från de sällsynta jordartsmetallerna har antimon den högsta försörjningsrisken.

Arbetet som beskrivs i denna avhandling syftade till att studera en process för att utvinna antimonföreningar från avfall. Det första steget var att identifiera antimonhaltiga föreningar, såväl som att karakterisera var och en av avfallsmaterialen. Eftersom det finns en begränsad mängd antimon som återvinns idag undersöktes flera tekniker för antimonutvinning inklusive lakning och termisk behandling. I litteraturen råder tvetydighet hos det termiska beteendet hos antimon (III) oxid, Sb2O3. Detta är olyckligt eftersom Sb2O3 är den viktigaste antimonföreningen ur ett industriellt perspektiv och den som används som utgångsmaterial i MOVs. Därför undersöktes även de termiska egenskaperna hos Sb2O3.

There are currently over 7 billion people on the planet with about 3 billion people living an urban lifestyle. Today, the 3 billion people living in urban areas generate an average of 1.2 kg/capita/day (1.3 billion tons per year) of municipal solid waste (MSW). With the current amount of waste generated we together need to implement long term, sustainable measures to deal with waste now and in the future.

This research focuses on the lesser known metalloid, antimony and the feasibility of recovering it from waste. Two types of waste were used (1) metal oxide varistors (MOVs) which contained a relatively large amount of antimony but has a small waste volume and (2) municipal solid waste incineration (MSWI) fly ash containing a small amount of antimony but a large volume is generated annually. The global supply of antimony is dominated by one country which has led the European Union to classify antimony as a critical raw material. Other than the rare-earth elements antimony has the highest supply risk.

The work described in this thesis was aimed at studying a process(s) to extract secondary antimony compounds from waste. The first step was to identify antimony containing compounds as well as characterize each of the waste materials. Since there is a limited amount of antimony being recycled today, several techniques were investigated for antimony extraction including leaching and thermal treatment. In literature, data on the thermal behavior of antimony (III) oxide, Sb2O3, shows significant ambiguity. This is unfortunate since Sb2O3 is the most important antimony compound from an industrial perspective and is used as a starting material in MOVs. Therefore, thermal properties of Sb2O3 were also investigated.

Ämneskategorier

Oorganisk kemi

Kemiska processer

Metallurgi och metalliska material

Drivkrafter

Hållbar utveckling

Styrkeområden

Produktion

Infrastruktur

Chalmers materialanalyslaboratorium

ISBN

978-91-7597-663-1

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4344

Utgivare

Chalmers tekniska högskola

10:an

Opponent: Prof. Vadim Kessler, Sveriges Lantbruksuniversitet, Institutionen för molekylära vetenskaper, Uppsala Sweden

Mer information

Skapat

2017-11-21