Biological Leaching and Chemical Precipitation Methods for Recovery

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Biological Leaching and Chemical Precipitation Methods for Recovery of Co and Li from Spent Lithium-ion Batteries Basanta Kumar Biswal, Umesh U. Jadhav, Munusamy Madhaiyan, Lianghui Ji, En-Hua Yang, and Bin Cao ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b02810 • Publication Date (Web): 17 Jul 2018 Downloaded from http://pubs.acs.org on July 22, 2018

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ACS Sustainable Chemistry & Engineering

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Biological Leaching and Chemical Precipitation Methods for Recovery of Co

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and Li from Spent Lithium-ion Batteries

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Basanta Kumar Biswal1,2,4*, Umesh U. Jadhav1,2, Munusamy Madhaiyan3, Lianghui Ji3, En-Hua

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Yang2, Bin Cao2,4

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Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, Singapore 637553

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School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798

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Biomaterials and Biocatalysts Group, Temasek Life Sciences Laboratory, National University of Singapore, 1 Research Link, Singapore 117604

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Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore

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*Corresponding author and present address

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Dr. Basanta Kumar Biswal, E-mail: [email protected], Tel: (+852) 6355-3867

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Department of Civil and Environmental Engineering

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The Hong Kong University of Science and Technology (HKUST), Hong Kong 1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract

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Spent Li-ion batteries (LIB) are highly rich in Cobalt and Lithium that need to be recovered to

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reduce shortage of these valuable metals and decrease of their potential environmental risks. This

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study applied bioleaching using Aspergillus niger strains MM1 and SG1, and Acidithiobacillus

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thiooxidans 80191 for removal of Co and Li from spent LIB under type 1 and type 2 conditions.

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Moreover, metal recovery was attempted from the fungal leaching solution by sodium sulfide,

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sodium hydroxide and sodium oxalate for Co, then Li using sodium carbonate. The findings of

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this work show that metal removal in fungal bioleaching under type 2 system was highly

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comparable or even better than bacterial or acid leaching. Significant quantity of Co (82 %) and

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Li (100 %) dissolution observed in strain MM1, however metal solubilisation was poor in strain

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80191 since only 22 % Co and 66 % Li solubilized. High amount of Co precipitated potentially

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as cobalt sulphide (100 %), cobalt hydroxide (100 %) or cobalt oxalate (88 %), and Li as lithium

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carbonate (73.6 %). Finally, results of this study suggest that fungal bioleaching could be an

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environmental friendly approach for solubilisation and recovery of considerable quantity of

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metals from spent LIB.

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Keywords: Bioleaching, Spent Li-ion batteries (LIB), Aspergillus niger, Acidithiobacillus

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thiooxidans, Chemical precipitation, Metal recovery 2


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Introduction

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In today’s technologically developed world, use of rechargeable Lithium-ion batteries (LIB) has

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risen steeply due to high demand for use in various electronic devices including mobile phones,

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digital cameras and personal computers 1. As a result, global Li-ion battery production has

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increased exponentially over the last decade from 2.04 billion in 2007 to 4.6 billion in 2011 2.

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Specifically in China, it is reported that the quantity and weight of discarded LIB in 2020 can

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exceed 25 billion units and 500 thousand tons, respectively 3. Thus, huge amounts of spent LIB

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wastes are entering solid waste stream, which may lead to dire consequences for the

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environment. Spent LIB are considered as “hazardous waste” due to presence several toxic components

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including cathodic materials containing heavy metal oxides of cobalt (LiCoO2), manganese

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(LiMn2O4) or nickel (LiNiO2) 4, and electrolytes such as LiPF6, LiBF4, LiCF3SO3 or Li(SO2CF3)2

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1, 5

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cathode in LIB due to high specific energy density and durability 6. These spent batteries contain

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up to 20 % of Co and 7 % of Li of the total weight of the generated waste 1. Co is an expensive

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metal due to its low abundance in nature and it has high toxicity effects to environments 5. Thus,

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recycling of these batteries is necessary since it will not only reduce environmental pollution that

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could arise by landfill disposal of these toxic metal-containing batteries, but it also conserves

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depletion of these valuable metal resources.

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. Among the three types of metal oxides, Lithium cobalt oxide (LiCoO2) is commonly used as

Extensive reports are published in literature on the use of several pyrometallurgical and hydrometallurgical methods for extraction of various metals including Co and Li from spent LIB 3



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7-8

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acids 9 or organic acids 5, 10, solvent extraction 11, chemical precipitation, hydrothermal 9 and

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electrochemical precipitation methods 11-12. In inorganic acid extraction, several acids namely

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HCl 13, H2SO4 14, and HNO3 15 have shown to be effective leaching agents. Furthermore, some

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authors have added reducing agents namely hydrogen peroxide (H2O2) to the inorganic acid (e.g.

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H2SO4) medium to accelerate metal dissolution 5, 16-17. Although, these hydrometallurgical and

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pyrometallurgical processes are widely employed for extraction of metals from spent batteries,

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however they require high energy, toxic chemicals, extreme physiochemical conditions, and at

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the end they release hazardous by-products to environments. Moreover, these methods may not

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suitable to recover pure precipitates of Co and Li salts due to high acidic nature as well as there

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may be co-precipitation of other compounds due to occurrence of anions such as chloride (HCl

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leaching), sulfate (H2SO4 leaching) or nitrate (HNO3 leaching). Hence, from an environmental

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point of view, a greener technology with less energy requirements and negligible environmental

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impact is required for recycling of these spent LIB.

. These recovery processes are primarily focused on use of acid leaching including inorganic

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Now-a-days, a promising method called bio-hydrometallurgical processes (bioleaching)

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has been widely adopted as an alternative to hydrometallurgical and pyrometallurgical methods

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for metal removal from a variety of waste materials including spent batteries 18-20. This process

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usually involves the use inorganic or organic acid producing microorganisms including bacteria

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and fungus which help in dissolution of metals from toxic waste materials 18. Biological leaching

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experiments are usually carried out in three different approaches called one-step, two-step and

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spent medium bioleaching 21-22. One-step is a classical process in which bioleaching is conducted 4


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by adding pregrowth culture inoculum to the leaching medium containing waste materials (e.g.

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battery powder). In two-step method, usually the acid producing organism is grown initially in

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the medium until it reaches the logarithmic phase, then battery powder is added to initiate metal

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leaching by produced bioacids. In the spent medium approach, the acid producing organism is

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cultured in the medium at first without battery powder until it entered the stationary phase, then

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cells are separated by centrifugation and filtration using appropriate filter paper. Leaching

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initiated by adding battery power to the cell-free spent medium containing one or more bioacids.

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Several comparative bioleaching studies have been performed using these three types of

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approaches and it was observed that in most cases the metal removal efficiency was highest in

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the cell-free spent medium bioleaching process 22. Two major chemolithoautotrophic acidophilic

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bacteria called Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, and fungal

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species namely Apsergillus niger have been widely used to extract metals from incineration fly

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ash, electronic scrap, waste slag, and spent catalyst 18. For spent LIB, a few biological leaching

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studies were carried out using A. ferrooxidans for mobilization of metals in spent Li-ion batteries

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23-25

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pure culture of A. thiooxidans, and only one published study on fungal leaching by A. niger

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strain 22, but no report on recovery of metals from the solution of fungal leaching.

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. However, still no information is available on recovery of Co and Li from spent LIB using

The primary objective of this work was to explore effective use of acid producing

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organisms (both fungus and bacteria) for extraction of Co and Li from spent LIB. Moreover,

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quantification of metal contents was done by inductively coupled plasma optical emission

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spectrometry (ICP-OES) in the solution obtained from the heat assisted inorganic acid digestion 5



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(HCl, HNO3, H2SO4 and aqua regia), then composition characterizing of untreated and acid

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treated spent LIB by X-ray diffraction (XRD). Finally, it was attempted to recovery Co

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potentially as cobalt sulphide, cobalt oxide and cobalt oxalate, and Li in the form of lithium

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carbonate from the fungal leached solution. To our knowledge, this is the first study that

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extensively studied bioleaching using two types of fungal strains (A. niger MM1 and SG1) and a

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bacterial stain (A. thiooxidans 80191), then endeavored recovery of two valuable metals from the

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fungal leaching solution by a new and well-established chemical precipitation methods.

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Experimental Section

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Preparation of spent Li-ion battery powder

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The crushed powder containing all components of different types of spent LIB was collected

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from a local waste recycling company in Singapore. The powder was sieved and the particle size

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below 300 µm was taken for washing by distilled water to remove electrolytes, then dried at 100

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°C. The dried powder was stored at room temperature to use in subsequent experiments.

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Determination of metal contents in spent Li-ion batteries by inorganic acid digestion

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In this experiment, inorganic acid digestion was conducted using four types of acids such as HCl,

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HNO3, H2SO4 and aqua regia (3:1 ratio of HCl and HNO3, respectively) to compare the metal

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dissolution efficiency between four acids. All reagent solutions were prepared in distilled water

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and all reagents used in this study were of analytical grade. Briefly, the triplicate extraction tests

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were performed in 250 mL conical flasks containing 50 mL of acid (concentration = 4M) and 6


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0.5g Li-ion battery powder. The suspension was heated in a hot plate to bring the solution

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temperature to 80 °C with constant stirring at 200 rpm for 2 hours. The acid leachate was filtered

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(pore size of filter paper: 0.45µm) and a fixed quantity of the filtrate was taken for quantitative

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analysis by ICP-OES (Perkin Elmer, Optima 8300) for detection of five metals including Co, Li,

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Cu, Mn and Ni as they are abundant in spent LIB reported in literature. The metal concentrations

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(mg/L) received from ICP-OES were converted to mg-Metal/g-Li-ion battery powder using the

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following formula. From the four acids, the acid that gives the highest metal removal was

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considered as a base line control to compare metal removal efficiency in bioleaching and

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chemical leaching methods investigated later.

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. × ℎ = ℎ − " # $ (1)

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Fungal and bacterial biological leaching of spent Li-ion batteries

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Fungal strains isolation, identification and inoculum preparation

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Aspergillus niger strains MM1 and SG1 were used in the present study. Strain MM1 was isolated

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from crown rot affected Jatropha roots, while the strain A. niger SG1 was isolated from air

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sampled in Singapore. Purified fungal isolates were cultured in YPD broth at 30 °C for 48h. Two

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mL of liquid culture was taken for DNA extraction using the MasterPureTM Yeast DNA 7



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Purification Kit (Epicentre Biotechnologies, USA) following manufacturer’s instructions. PCR

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reactions were carried in 40 µL 1X buffer mixture containing 2.5 mM dNTP, 50 µM each

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primer, 50 ng of total DNA and 3 units of Taq DNA polymerase (i-DNA Biotechnology,

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Singapore). PCR thermal cycling programs were set as follows: 95 °C for 10min, 30 cycles of 95

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°C for 1 min, 61.8 °C for 1 min and 72 °C for 1 min and final extension for 5 min at 72 °C. The

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forward primer ITS1 (5'-TCCGTAGGTGAACCTGCGG-3') and reverse primer ITS4 (5'-

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TCCTCCGCTTATTGATATGC-3') 26 were used to amplify the ITS region of the nuclear rRNA

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operon spanning the 3’ end of the 18S rRNA gene, the first internal transcribed spacer (ITS1),

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the 5.8S rRNA gene, the second ITS region and the 5’ end of the 28S rRNA gene 27. Gel-purified

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PCR products were taken for sequencing with the Big-Dye sequencing method (Life

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technologies, USA), and sequences were analyzed by BLAST at the National Center for

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Biotechnology Information (NCBI) website. The internal transcribed spacer (ITS) sequences

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have been submitted to the NCBI GenBank under accession no. MH091025 and MH091026 for

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the strain MM1 and SG1, respectively.

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To prepare inoculum, the two fungal strains were initially cultivated on 3.9 % (w/v)

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potato dextrose agar plates (PDA, Sigma-Aldrich, Singapore) as described previously 28. The

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plates were incubated at 30 °C for nearly a week, then spores were recovered from the plates by

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washing with sterile distilled water. The number of spores in the suspension was determined

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using a Nikon Eclipse 80i microscope equipped with CFI Plan Apochromatic objectives (Nikon,

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Japan), and appropriate dilution was made with sterile distilled water to make the suspension

8


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density of nearly 107 spores/mL which was taken for inoculum (1 %, v/v) for fungal bioleaching

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experiments.

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Fungal bioleaching: Shaking flask type 1 and type 2 experiments

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The sucrose medium containing the following chemicals (g/L) such as sucrose (100), NaNO3

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(1.5), KH2PO4 (0.5), MgSO4.7H2O (0.025), KCl (0.025), and yeast extract (1.6) was used to set

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up bioleaching experiments 28. The leaching experiments were carried out following the reported

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procedures 29. The type 1 leaching was conducted in 250 mL conical flasks containing 50 mL of

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sterile sucrose media, 0.25 % (w/v) of autoclaved LIB powder and 0.5 mL (1 %, v/v) of the A.

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niger MM1/SG1 cultures. The flaks were incubated at a temperature of 30 °C with shaking at

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200 rpm. Abiotic control flasks containing sterile sucrose medium and Li-ion battery powder

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were also set up in same conditions.

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In type 2 bioleaching, initially A. niger strains were cultivated, then Li-ion battery

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powder was added to cells free medium to initiate leaching process. Briefly, in 250 mL conical

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flasks, 50 mL of sterile sucrose media and A. niger strain (1 %, v/v) were added, then flasks were

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placed in an incubator shaker operating at 30 °C and 200 rpm. After two days, the A. niger was

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fully grown as indicated by pH drops from initial 6.0 to nearly 3.5. The media was centrifuged

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and filtered (pore size of PES filter paper: 0.22 µm, Pall Corporation) to remove fungus biomass.

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50 mL of filtered supernatant was taken in 250 mL conical flasks to start leaching experiments

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by adding autoclaved Li-ion battery powder (0.25 %, w/v). Appropriate abiotic controls

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containing sterile sucrose medium and Li-ion battery powder were also run in parallel. On each 9



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sampling day, 3 ml of suspension from both types of leaching experiments was withdrawn for

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determination of pH, metal analysis by ICP-OES, and sucrose concentrations by HPLC

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(Shimadzu LC-20AD Prominence Liquid Chromatography). Metal removal efficiency in

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bacterial and fungal leaching was calculated by comparing with the results of acid leaching and

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using the following equation.

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% & % =

( − ) × 100 2 (

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Where Ca and Cb are the metal concentrations measured in acid leaching and bioleaching

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experiments.

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Bacterial strain inoculum

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The bacterial strain, Acidithiobacillus thiooxidans strain 80191 used in this study was obtained

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from the Food Industry Research and Development Institute (FIRDI), Taiwan. Strain 80191 was

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cultured on the basal 317 medium following the reported protocol 30. The basal 317 medium

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contains the following reagents per litter of distilled water: 0.3 g (NH4)2SO4, 3.5 g K2HPO4, 0.5

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g MgSO4.7H2O, and 0.25 g CaCl2. The pH of the medium was adjusted to 4.5 by 1N sulfuric

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acid. Sterilized elemental sulfur powder (1.0 %, w/v) was added to medium as an energy source

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for growth of strain 80191. The flasks containing the media and 80191 strain were placed in a

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shaking incubator which was set to operate at 30 °C temperature and 150 rpm shaking speed.

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After an incubation of 10 days, liquid culture was used as an inoculum (10 % v/v) for

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bioleaching tests as the decrease of pH reached steady state (pH dropped from 4.5 to 2.5). 10


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Bacterial bioleaching: Shaking flask type 1 and type 2 experiments

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The experimental procedures for the type 1 and type 2 bacterial bioleaching were similar to

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fungal bioleaching as described previously. The leaching tests were done in 250 mL glass flasks

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having 50 mL sterile basal 317 medium, 0.25 % (w/v) Li-ion battery powder and 10 % (v/v) A.

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thiooxidans 80191 inoculum (type 1, culture medium pH: 3.3). For type 2 leaching, battery

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powder was added to the biomass free filtered media (0.22 µm PES filter paper, Pall corporation)

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that was recovered by after culturing 80191 strain (culture medium pH: 2.4). In this study, types

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1 and 2 leaching processes were investigated to observe the difference of metal leaching

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characteristics in two processes since LIB contain toxic cobalt which may inhibit the growth of

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leaching organisms in type 1 process.

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Chemical leaching experiment

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Chemical leaching of the spent LIB powder was performed using commercially available citric

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acid and sulfuric acid to compare their metal leaching efficacy with biologically produced acids

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by fungal and bacterial strains, respectively. The concentration of citric acid (102.4 mM) and

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sulfuric acid (10.2 mM) was same to the acid concentration produced by growth of pure culture

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of fungal (MM1) or bacterial (80191) strains without spent LIB (Table 2). The medium

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conditions used in bioleaching testes were replicated here and triplicate experiments were run in

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250 conical flasks containing 50 mL acid solution and 0.25 % (w/v) spent LIB powder. The

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flasks were placed in an incubator maintained at 30 °C temperature and shaking speed of 200

11



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rpm. Samples were withdrawn and filtered for quantification of metal concentrations by ICP-

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OES.

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Analysis of bio-acid production in fungal and bacterial leaching studies

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Analysis of consumption of sucrose and production of organic acids in fungal leaching

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In the leaching media, the changes of sucrose concentrations due to fungal growth and

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production of organic acid metabolites including citrate, oxalate and gluconate were measured by

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High Performance Liquid Chromatography (HPLC) equipped with Refractive Index Detector

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(RID) and diode array type of UV detector (DAD) (Shimadzu LC-20AD Prominence Liquid

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Chromatography). The mobile phase used was 5 mM sulfuric acid, at a flow rate of 0.7 ml/min at

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50 °C. For all samples, standards solutions of sodium citrate, disodium oxalate, sodium

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gluconate and sucrose were analysed. Appropriate dilutions of filtered samples were made for

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HPLC analysis.

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Measurement of H2SO4 production in bacterial leaching

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Biological production of sulphuric acid (H2SO4) in A. thiooxidans 80191 leaching medium was

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continuously monitored using the titration method published earlier 30-31. In brief, 10 mL of the

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biological leached solution was titrated with 0.1N NaOH solution using phenolphthalein as an

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indicator. The concentration of sulphuric acid is determined from the following acid-base

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titration equation.

248 12


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2-./ + /1 2.3 → -1 2.3 + 2/1 .

(3)

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Recovery of Co and Li from fungal leached liquor

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Attempts were made for recovery of dissolved Co and Li from the type 2 fungal bioleaching

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solution by a new and highly efficient chemical precipitation methods. Leached liquor was first

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purified by centrifugation (10,000xg), then filtration (0.45 µM PES filter, Pall Corporation) to

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remove suspended particles. For each type of chemical precipitation tests, 25 mL of the filtered

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solution was used. Prior precipitation experiments, contents of Co and Li in the purified fungal

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leached liquor were determined by ICP-OES. First, recovery of Co was initiated by three

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independent chemical approaches such as by adding sodium sulphide (Na2S), sodium hydroxide

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(NaOH) and sodium oxalate (Na2C2O4) to potentially precipitate cobalt sulphide (CoS), cobalt

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hydroxide [Co(OH)2] and cobalt oxalate (CoC2O4.2H2O), respectively. Precipitation of Co using

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sodium hydroxide and sodium oxalate have been reported before 2, 32, however, in this work, it is

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attempted first time to recover Co in the form of cobalt sulphide since it is used as cathode active

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materials for lithium-rechargeable batteries 33. Three precipitation methods were investigated

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here to compare their Co recovery performance. Each precipitation reaction was conducted

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independently at room temperature unless otherwise stated, and it was not required to do any pre-

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treatment of adjusting pH from acidic to neutral/alkaline of the filtered liquor for Co recovery by

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sodium sulphide or sodium oxalate. To recover Co as cobalt sulphide, the reaction was

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conducted in a 50 mL glass beaker containing 25 mL of impurities free fungal leaching solution,

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then added sodium sulphide continuously with mixing provided by a magnetic stirrer until no 13



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precipitation formed. Similar procedures were followed to recover Co as cobalt oxalate by

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adding sodium oxalate. However for cobalt hydroxide precipitation, the pH of the filtered liquor

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was adjusted to alkaline (pH = 12) using 1M NaOH solution 32. After the recovery of Co, the

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remaining suspension was filtered (0.45 µM PES filter, Pall Corporation), then concentrated by

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heating at 100 °C until volume of the solution reduced from 25 mL to nearly 10 mL. Lithium

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precipitation was performed by treating with sodium carbonate (Na2CO3) at pH 12 to initiate

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precipitation of Lithium carbonate (Li2CO3) 32. After completion of each precipitation reaction,

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the suspension was rested for nearly an hour to settle the formed solid products, then the

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supernatant solution was removed and filtered, and analysed by ICP-OES for determination

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metal concentrations in the solution which was used to calculate metal removal efficiency in

280

each process. The precipitation reactions for Co and Li recovery using different reagents could

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be expressed as follows.

282 283

16 6 (5 + -1 2 → 27 + 2-(5

(4)

284

16 6 (5 + 2-./ → ./18 + 2-(5

(5)

285

16 6 (5 + -1 1 .3 + 2/1 . → 1 .3 . 2/1 .8 + 2-(5

(6)

286

6 6 2(5 + -1 .9 → 1 .9 7 + 2-(5

(7)

287 288

X-ray diffraction (XRD) analysis

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The constituents of Li-ion batteries before and after acid leaching were identified using XRD

290

analysis. The XRD was performed with a Bruker AXS D8 advance powder diffractometer 14


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(Bruker, USA) by using Cu Kα radiation. The XRD patterns were recorded in the 2θ range from

292

10° to 80° at a scan rate of 2°/min.

293 294

Statistical analysis

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All experiments were performed as triplicate and processed independently. Average values were

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taken for all analysis and standard errors associated with the data were appropriately reported.

297

Statistical differences of metal removal efficiency between fungal, bacterial and inorganic acid

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leaching processes were computed by the two-tailed unpaired Student’s t-test with the GraphPad

299

software. The test statistical significance was evaluated at a P value of ≤ 0.05.

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Results and Discussion

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Determination of metal contents and characterization of spent Li-ion batteries

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At first four types of acid leaching (HCl, HNO3, H2SO4 and aqua regia) were employed to

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quantify concentrations of five metals namely Co, Li, Cu, Mn and Ni in spent LIB powder, and

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the results are given in Table 1. Among the four leaching agents tested, Co dissolution was

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highest in HCl (159.6 mg/g spent LIB). However, HNO3 was efficient for extraction of other

308

four metals including Li = 20.7, Cu = 6.15, Mn = 0.70 and Ni = 0.38 mg/g spent LIB. Finally,

309

the metal removal was very poor in H2SO4 digestion. Many previous studies on inorganic acid

310

leaching have demonstrated that Co and Li can be efficiently extracted (up to 99 %) from spent

311

LIB using 4N HCl 1, 4 15



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Table 1: Metal contents in spent Li-ion batteries determined by various inorganic acids Leaching of metals at different inorganic acidsa Metal (mg/g) 4N HCl 4N HNO3 4N Aqua regia 4N H2SO4 b Cobalt (Co) 159.6±14.1 146.6±2.0 144.6±3.6 44.7±0.4 b Lithium (Li) 12.9±1.1 20.7±1.6 5.0±0.9 8.4±0.1 b Copper (Cu) 6.08±0.1 6.15±0.2 2.93±0.1 2.76±0.1 Manganese (Mn) 0.65±0.1 0.70±0.1b 0.31±0.1 0.41±0.1 b Nickel (Ni) 0.12±0.1 0.38±1.6 0.26±0.9 0.31±0.1 a Conditions: Temperature: 80 °C, shaking: 200 rpm, time: 1 hr, liquid to solid ratio: 10 b

Highest value among the four types acid leaching used to calculate leaching efficiency

313 314

The original and HCl treated spent LIB powder were characterised by XRD techniques to

315

observe the changes of chemical components due to acid digestion [Figures 1(a)]. In the original

316

spent battery samples, two major peaks were identified in which one peak was assigned as

317

cathodic material, Lithium Cobalt oxide (LiCoO2) at 2θ = 19 while the other peak was identified

318

as graphite (anode) at 2θ = 27. Acid treatment by HCl caused dissolution of most of the cathodic

319

material since LiCoO2 peak was completely absent in the acid treated samples [Figure 1(b)].

320

16


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321 322

Figure 1: XRD analysis of original spent Li-ion batteries powder of particle size < 300 µm

323

before (a) and after HCl digestion (b).

324 325

pH characteristics and production of acids in fungal and bacterial bioleaching

326

The pH of the leaching media without (abiotic) and with MM1 and SG1 strains is presented in

327

Figure 2 (a). The type 2 leaching was initiated after an initial growth of fungus in the medium

328

that resulted pH of 2.40, and the pH did not significantly change at the end of the experiments. In

329

type 1, the pH of all samples at the start of experiment was 6.22, however the pH of A. niger

330

inoculated samples dropped nearly to half (pH= 3.35) after 48 hours of incubation, then pH did

331

not significantly change throughout the experiments. The decrease of pH in A. niger leaching

332

media was correlated to the sucrose consumption rate by A. niger strains as shown in Figure 2

333

(a). The sucrose concentration in the bioleaching medium significantly decreased after 48 hours

334

of incubation, i.e. initial sucrose concentrations of 100 g/L reduced to less than 0.5 g/L in 48

335

hours. The change of pH in the media is an indication of growth A. niger strains using sucrose as 17



336

a carbon source and production of organic acid namely citrate. The significant pH drops could

337

be due to production of one or more organic acids as suggested in previous studies on metal

338

mobilization in electronic scrap by two fungal strains namely A. niger and Penicillium

339

simplicissimum 34. In our studies, only citric acid was detected in two types fungal leaching

340

media (41 – 71 mM) in the presence of LIB (Table 2).

Page 18 of 45

341

342 343

Figure 2: (a) Fungal leaching pH profile of abiotic and A. niger MM1 and SG1 strains in type 1

344

and type 2 approaches, and sucrose concentrations in abiotic, MM1 and SG1 strains under type 1

345

condition. There was no sucrose in the type 2 medium as all were utilized for fungal growth.

346

MM1 (T1) pH = pH of MM1 sample run in Type 1, MM1 (T2) pH = pH of MM1 sample run in

347

Type 2, SG1 (T1) pH = pH of SG1 sample run in Type 1, SG1 (T2) pH = pH of SG1 sample run

348

in Type 2, MM1 (T1) Sucrose = Sucrose concentration in MM1 sample run in Type 1, SG1 (T1)

349

Sucrose = Sucrose concentration in SG1 sample run Type 1 condition; (b) bacterial leaching on

18


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350

changes of pH and production of sulfuric acid (H2SO4) in abiotic and biotic A. thiooxidans 80191

351

samples run in type 1 (T1) and type 2 (T2) conditions.

352 353

The changes of pH and production of sulphuric acid (H2SO4) in bacterial leaching is

354

shown in Figure 2(b). In all samples, the initial pH increased after addition of LIB powder. In

355

biotic type 1 samples, the pH decreased from 4.5 to 3.1, which indicate the growth of A.

356

thiooxidans 80191. It is well known that growth of A. thiooxodans produce sulfuric acid which

357

cause the decrease of pH in the media 35. In our study, 10.2mM H2SO4 produced in the fully

358

grown 80191 culture, then it decreased to 2.6mM at the end of bioleaching (type 2) in 40 days

359

period (Table 2). In Type 1 leaching test, 1.74 mM H2SO4 observed at the end of test. A previous

360

study on bioleaching of metals from steel slag by A. thiooxidans showed production of 16 mM

361

sulfuric acid in 14 days 30. In our study, the pH declined only by nearly one and half unit (4.5 to

362

3.1) which may be due to slow growth of A. thiooxidancs by toxic effect of metals in Li-ion

363

batteries. In type 2 leaching where 80191 was grown in the absence of Li-ion batteries, the pH of

364

the leaching solution was 2.4 while the pH appears to increase during leaching experiments and

365

the final pH was reached at 3.0. The increase of pH could be due to decrease of sulfuric acid

366

contents as the acid may be utilized to leach metals from spent batteries. Finally, the pH of the

367

abiotic samples remains unchanged after an initial increase contributed by the residual alkaline

368

materials present in Li-ion batteries.

369 370 19



Page 20 of 45

371

Table 2: Production of citric acid by A. niger MM1/SG1 strain and sulfuric acid by A. thiooxidans 80191 at various conditions Citric acid (mM)a MM1 SG1

Sample typed Pure cultureb

102.4±4.5

76.9±3.5

10.2±0.74

40.7±1.6

43.1±2.4

1.7±0.43

c

70.8±3.4

59.5±6.0

2.6±0.56

Type 2 bioleaching

Oxalic and gluconic acids were not detected in the medium by HPLC

b c

80191

c

Type 1 bioleaching a

Sulfuric acid (mM)

Measured when the cells were fully grown as indicated by no pH change in medium

Measured at the end of bioleaching experiment

d

Triplicate samples were analysed independently

372 373

Fungal bioleaching for removal of Co and Li from spent Li-ion batteries

374

The removal characteristics of two valuable metals including Co and Li from the complex

375

mixture of spent LIB powder using MM1 and SG1 strains processed in type 1 and type 2

376

approaches are shown in Figures 3 (a) and (b). The leaching study was carried out with a pulp

377

density of 0.25 % (w/v) since the preliminary study with 0.5 % (w/v) pulp density showed no

378

growth of fungus. The metal removal increased with an increase of incubation period for both A.

379

niger strains, and the both A. niger stains had similar metal dissolution profiles. Between two

380

types of leaching, type 2 conditions favoured more leaching of metals compared to type 1. The

381

metal concentrations (mg/g-spent LIB) in type 2 solution were 131.1 (82 %) and 24.2 (100 %)

382

for Co and Li, respectively, after an incubation period of 40 days using MM1 strain. The type 1

383

leaching removed 107.1 mg/g (67 %) and 18.0 mg/g spent LIBs (100 %), Co and Li,

20


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384

respectively. Here, the percentage removal of metal was calculated by comparing with acid

385

leaching data (Co: 159.6 and Li: 20.7 mg/g spent LIB, Table 1) as reported previously 22.

386

387 388

Figure 3: Fungal leaching profile of Cobalt (a) and Lithium (b) from spent LIB powder in abiotic

389

control, and by A. niger MM1 and SG1 strains using type 1 (T1) and type 2 (T2) processes.

390 391

The metal dissolution from spent LIB by A. niger could be due to secretion of organic

392

acids in the leaching media 18. In our study, only citric acid is detected in both type 1 and type 2

393

leaching conditions as well as in the pure culture grown without spent LIB powder. Quantity of

394

citric acid (59.5 – 70.8 mM) was significantly higher in type 2 than type 1 leaching medium (41

395

– 43 mM) (P .? ↔ : /? .? + / 6

(10)

434

: /? .? + 6 ↔ A

(11)

436

: /1 .: ; + .1 → : /B .: ; + /1 .1

(12)

437

: /B .: ; + /1 . → : /1 .? ; +/1 .1

(13)

438

/1 .1 → /1 . + 1 .1

(14)

439

: /1 .? ↔ : / .? + / 6

(15)

435

23



440

Page 24 of 45

: / .? + 6 ↔ ; A

441 442

: /1 .: ; + 4.5.1 → 31 /1 .3 .A + 3/1 .

(16)

443

1 /1 .3 ↔ 1 /.3 + / 6

(17)

444

1 /.3 + 6 ↔ .A A

(18)

445 446

Bacterial bioleaching for removal of Co and Li from spent Li-ion batteries

447

The leachability of the two predominant metals namely Co and Li from spent LIB using A.

448

thiooxidans as a leaching microorganism are given in Figures 4 (a) and (b). In this work, type1

449

(leaching due to fungal growth in presence of spent batteries) and type 2 (leaching using spent

450

microbial solution containing bioacid, H2SO4) were done to compare metal solubilisation in two

451

processes. The results showed that the metal solubilisation rate in type 2 method was remarkably

452

higher than type 1 (P

Biological Leaching and Chemical Precipitation Methods for Recovery

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