Screening for Ceramic and Leaded Contaminants in Glass Recycling Streams using Handheld X-ray Fluorescence (HHXRF)

Analyzers

Dillon McDowell and Alex Thurston

APCNDT 2017

Overview

¡  The glass recycling industry and recycling process – Dealing with contamination – Ceramic glass issues

¡  Brief introduction to XRF

Glass Recycling

¡  The majority of recycling concerns glass containers (bottles, jars, etc.) –  Primarily soda glass

¡  Glass is recovered, sorted, and cleaned to be turned into furnace-ready cullet

¡  Soda glass can be completely recycled without any loss of quality

¡  On average, newly produced glass containers consist of ~33% recycled content

¡  Material recovery facilities (MRFs) may process as much as 20+ tons of cullet per hour

¡  Material quality is key to hitting efficiency targets and reducing process cost

Contamination and Ceramic Glass

¡  A variety of techniques that handle different types of contamination

– Magnetic sorting (metallic contamination)

– Vacuum suction and vibrating screens (light materials — paper, plastic, etc.)

– Visual/infrared sorting (opaque materials — stones, gravel, etc.)

¡  Some materials are difficult to separate through automated techniques

– Other glass types (borosilicate, leaded crystal)

– Ceramic glasses

¡  Ceramic glasses are increasingly common in variety of products

– Cookwear – Manufactured good – Electronics (smartphone screens)

¡  Has many of the same physical properties as recyclable glass (weight, density, appearance, etc.)

¡  However… – Has a different chemistry (unique

ceramic elements) – Has a higher melting point (doesn’t

fully melt in a furnace)

Ceramic Glass Issues

¡  Increase furnace downtime and/or may irreparably damage them

¡  Large risk to cutting systems – Water-cooled scissors may be damaged attempting to cut into ceramic glass

¡  The final product is rendered defective and unusable by impurities – Glass products with ceramic may crack or shatter (sometimes explosively)

X-ray Fluorescence Spectroscopy

¡  First demonstrated in 1912

¡  First handheld systems appeared in late 1990s

¡  Exciting a sample with X-rays generates a fluorescence response unique to the elements in the sample

¡  Measuring that response provides compositional information

¡  Used for various commercial applications – Metals/alloys – Soil/geologic samples – Consumer products

Instrumentation

¡  Olympus Vanta™ handheld XRF analyzer – Model: VCR (rhodium (Rh) anode, silicon drift detector

(SDD )system) – 8 mm excitation point (down to 3 mm with collimation)

¡  Used “Soil” method as basis for testing – Compton normalization technique – Typically used to test SiO2 - based samples – Offers various excitation conditions (beams) for a variety

of elements

¡  Testing performed using a Vanta workstation – Enables consistent sample presentation – Closed-beam system while in workstation

Experiment

¡  Gauge the effectiveness of HHXRF in identifying various elements – Ceramic identifiers: titanium (Ti), zirconium (Zr), strontium (Sr), and zinc (Zn) – Additional identifiers: iron (Fe), copper (Cu), and lead (Pb)

¡  Stage 1: Certified material – Test certified glass samples (NIST 610, NIST 612) – Establish a baseline calibration

¡  Stage 2: Test recovered ceramic glass samples – Use the calibration from the previous stage – Sample composition also verified via lab testing (ICP) – Focus on effects of sample size and analysis time

Stage 1 — Certified Materials

¡  Samples chosen for variety

¡  Initial readings used to established calibration factors; the samples were retested using corrections

¡  Each sample was tested for 30 seconds in beams 1 and 2 (60 seconds total per test)

¡  Values shown are the averages of 10 repeat tests

¡  Samples are quite thin (~3 mm), so multiples were used to minimize thickness biasing for initial calibration

¡  Overall, very consistent response from HHXRF

NIST 610

Element Assay (ppm) +/- 2σ XRF (ppm) +/- 2σ

Ti* 437 30 496.8 84.8

Zr[8] 440 2 445.4 16

Zn* 433 4 428 12

Pb 426 1 427 12

Cu 415 29 443 10

Fe 458 9 447.4 18

Sr 515 0.5 437.6 15.2

NIST 612

Element Assay (ppm) +/- 2σ XRF (ppm) +/- 2σ

Ti* 50.1 0.8 122.75 58

Zr[8] 36 1.3 46.8 4

Zn[9] 40 5 36.8 4

Pb 38.6 0.2 41.6 4

Cu* 35 3.3 36 2

Fe 51 2 43.6 6

Sr 78.4 0.2 83.2 4

Stage 2 — Recovered Glass Ceramic Samples

¡  Samples were provided from a major producer/recycler of glass and class ceramic products

¡  Samples were independently assayed by supplier via ICP-MS

¡  Samples consisted of: –  #1: Heavy ceramic glass (high Zr, Sr, and Ti) –  #2: Leaded crystal glass (high Pb) –  #3: Light ceramic glass (high Sr)

¡  In addition, a certified pure quartz (SiO2) sample was tested to help ensure lack of potential false positives

¡  Samples were tested using only 1 beam at various test times to test the effect of long vs. short analysis for sorting purposes

Sample 1 — Heavy Ceramic Glass

Sample 1 — Glass Ceramic (High Zr, Sr, Ti)

XRF Concentrations

Element ICP Result 30 Sec +/- 2σ 10 Sec +/- 2σ 3 Sec +/- 2σ

Ti 2705 71041.6 1884.4 71647.4 3297.2 71326.8 6047.6

Zr 11105 24020 1656 23403.8 2754.4 23627 5140.4

Zn 3856 6890.2 158 6910.2 275.6 6993.2 512.4

Pb - 208.8 27.6 208 48 221.8 89.2

Cu - 188 28.4 198 50 192.6 92.4

Fe 314 - - - - - -

Sr 77034 >10% 9415.2 >10% 15659.6 >10% 29120.4

Sample 1 — Leaded Crystal

Sample 2 — Leaded Crystal Glass (High Pb)

XRF Concentrations

Element ICP Result 30 Sec +/- 2σ 10 Sec +/- 2σ 3 Sec +/- 2σ

Ti 118 - - - - - -

Zr 222 - - - - - -

Zn - 94.5 45.5 125 80 - -

Pb 205069 >10% 19880.4 >10% 35518 >10% 68998.4

Cu - - - - - - -

Fe 287 411 77.6 393 135.2 541 260

Sr 161 - - - - - -

Sample 3 — Light Ceramic Glass

Sample 3—Light Glass Ceramic (Low Sr)

XRF Concentrations

Element ICP Result 30 Sec +/- 2σ 10 Sec +/- 2σ 3 Sec +/- 2σ

Ti - - - - - - -

Zr - 155.4 10 154.6 17.6 156.6 32.4

Zn - 46.4 4 49.4 6 45.4 11.2

Pb - - - - - - -

Cu - - - - - - -

Fe 70 23.8 6 21.4 10 31.5 20

Sr 1099 1695.8 57.2 1698.2 98.8 1712.6 184

Small Fragment Testing

¡  Broke off a small fragment of each sample (~1 mm diameter) and repeated stage 2

¡  Wanted to simulate the smallest possible fragment that may be present in a cullet stream

– Can also mimic possible inclusions that may appear in final container products

¡  Results largely qualitative, but demonstrate detection capabilities of ceramic elements

In-Line XRF Systems

¡  The technique shown here has already been scaled to an inline system: the X-STREAM™ XRF analyzer

¡  Used currently for both scrap sorting as well as for glass

¡  Uses multiple source/detector arrays instead of a single source/detector (like in HHXRF)

¡  Goal is qualitative analysis: –  Identify the presence/absence of

ceramic elements – Remove ceramics from a cullet stream

via air blast

¡  Can process as much as 28 tons/hour

Summary

¡  The nature of ceramic contamination is localized fragments with a high concentration of ceramic elements (Zr, Zn, Sr, and Ba)

¡  HHXRF can effectively screen ceramic elements – Accurate quantization, while achievable, requires more sample preparation and testing

time – Sorting/screening can be done effectively through qualitative testing via XRF

¡  HHXRF can identify even small fragments of ceramic material – Maintain consistent detection of common ceramic tracers

¡  Technique can be scaled to in-line systems – Qualitative sorting based on fluorescent signal from ceramic elements