MCHM CHEMICAL PROPERTIES, TRANSPORT, AND FATE IN COAL PREPARATION PLANTS

Size: px

Start display at page:

Download "MCHM CHEMICAL PROPERTIES, TRANSPORT, AND FATE IN COAL PREPARATION PLANTS"

Joshua Lee
6 years ago
Views:

1 MCHM CHEMICAL PROPERTIES, TRANSPORT, AND FATE IN COAL PREPARATION PLANTS Aaron Noble, PhD Assistant Professor Mining Engineering Tom He, PhD Environmental Geochemist West Virginia Water Research Institute April 1, 2015

2 BACKGROUND

3 BACKGROUND January 9, 2014: Elk River Chemical Spill 10,000 gallons reportedly leaked into Elk River, Charleston WV American Water intake 1.6 miles downstream Contaminated water in system before WVAW can shut off intake Do not use order issued to 300,000 customers In effect for about 10 days

4 West Virginia American Water Freedom Industries 1.6 miles Civic Center

5 Relative Google Search Frequency 4-METHYLCYCLOHEXANE METHANOL Chemical notably involved in the spill Was really important this time last year MCHM "Mountaineers" "MCHM" 1/1/2005 1/1/2007 1/1/2009 1/1/2011 1/1/2013 1/1/2015

6 MCHM TOXICITY What we knew at the time: Not well characterized Acute oral dose-825 to 2,000 mg/kg body weight, test results from rats Irritant Skin Eyes Lungs Information based on concentrated MCHM

7 MCHM TOXICITY What we have learned since then: CDC Threshold = 1 mg/ L MCHM in drinking water. Aqueous Smelling Threshold WVTAP = 0.15 μg/l VT = 1.2 μg/l

$MCHM USES MCHM is a frother used in froth flotation Flotation is used to treat the finest fraction of coal$

8 MCHM USES MCHM is a frother used in froth flotation Flotation is used to treat the finest fraction of coal (<150 microns) In flotation, coal attaches to air bubbles and floats forming a layer of froth. Feed Coal Air Rock

9 MCHM USES Flotation requires: A lot of small air bubbles to capture the coal. A fairly stable froth that can cleanse the mixture. Bubble size is very important. MCHM regulates bubble size by preventing coalescence. AIR MCHM AIR Feed Coal Air Rock

10 COAL PREPARATION PLANT Circuit Feed From Head Tank D&R Screens Sizer Raw Coal Deslime Screens Dense Medium Vessel D&R Screens Stoker Centrifuge D&R Screens D&R Screens Dense Medium Cyclones Centrifugal Dryer Classifying Cyclones Compound Spirals Dewatering Screen Sieve Bends/ Clean Coal Cyclones Deslime Cyclones (Optional) Flotation Thickener Screen-Bowl To Head Tank Clean Coal Waste Disposal

11 COAL PREPARATION PLANT Circuit Feed From Head Tank Reagent Pump Clean Coal To Head Tank Waste Disposal

12 OUR QUESTION Spilling 10,000 gallons of anything into the river at one time is usually a bad thing But what about the ~½ gallon of MCHM used daily by several active coal prep plants?

70 Prep plant throughput 5,000 gpm 18,925 L/min Assumes: No MCHM adheres to coal or tailings No decomposition

13 ESTIMATED MAXIMUM MCHM CONCENTRATION IN A VERY HIGH USE SETTING: MET COAL, HIGH FINES CONTENT MCHM density MCHM use 0.88 g/ml 7,500 gal/yr gpm ml/min g/min 47,529 mg/min Slurry liquid/solid 0.70 Prep plant throughput 5,000 gpm 18,925 L/min Assumes: No MCHM adheres to coal or tailings No decomposition in the slurry impoundment MCHM concentration 3.59 mg/l What about the smell test? Source: Ziemkiewicz, WVCA Meeting, 2014

14 OUR QUESTIONS How does MCHM partition between the coal and tailings? Feed MCHM Does significant MCHM drain from the tailings impoundment/ underground storage? What other mechanisms control MCHM concentration? Tailings MCHM Coal

15 RESEARCH APPROACH Site Sampling Goal: Directly measure MCHM in plant and discharges Laboratory Tests Goal: Explain the plant data by examining the transport mechanisms

16 SITE SAMPLING

17 SITE SAMPLING Two sites selected for MCHM partitioning study: Similar Site A Northern Appalachia Conventional Flotation Slurry Feed: 9,600 gpm MCHM: 6 7 PPM Underground Injection No Deslime Site B Central Appalachia Column Flotation Slurry Feed: 1,200 gpm MCHM: 6 10 PPM Surface Impoundment Deslime Different Different

18 DATA COLLECTION Collected water/slurry/solid samples from various streams in plant: Flotation Feed Flotation Con Flotation Tailings Collected water samples from environmental discharges Impoundment Drain Thickener Feed Thickener UF Thickener OF Groundwater monitoring wells Analyzed water for MCHM (EPA Method SW8015C) Analyzed solids for size, ash, moisture. Filter Effluent Clean Coal Etc.

19 SITE A DATA: SAMPLING LOCATIONS 9,600 gpm Flotation Vacuum Filtration Clean Coal To Head Tank 6 7 PPM MCHM Underground Injection Monitoring Well

20 SITE A DATA: CONCENTRATIONS 4 μg/l 30 μg/l 2 μg/l ND ND, ND, ND 1 μg/l ~ 1 PPB ND: <2 μg/l 2 μg/l

21 SITE A DATA: MASS DISTRIBUTION 0.1 % 0.05% 0.05% 99.9% 0% 100% Somewhere other than the water. <<0.1% 0%

22 SITE B DATA: SAMPLING LOCATIONS Deslime Cyclones 1,200 gpm Flotation Screenbowl Centrifuge Clean Coal 6 10 PPM MCHM To Head Tank Waste Disposal Impoundment

23 SITE B DATA: CONCENTRATIONS 12,736 μg/l 7,924 μg/l 11,263 μg/l 879 μg/l 3 μg/l ND ND, ND 1 μg/l ~ 1 PPB ND: <2 μg/l ND

24 SITE B DATA: MASS DISTRIBUTION 100% 26% 100% 74% 3% 77% 0.2% 0% 0% Somewhere other than the water. 0%

25 PUTTING EVERYTHING TOGETHER

SUMMARY In both cases, we observed a mysterious MCHM disappearance. Was the plant operating at a lean dosage? Did we randomly mishandle particular samples?

26 SUMMARY In both cases, we observed a mysterious MCHM disappearance. Was the plant operating at a lean dosage? Did we randomly mishandle particular samples? Did the lab systemically mishandle the samples? Is the MCHM sorbing or volatilizing? No, we would have observed poor plant performance. No, downstream samples corroborate disappearance. Can t be ruled out. Hmm

27 VOLATILIZATION? Frothers are known to quickly volatilize when exposed to agitation. Our laboratory data confirms that MCHM volatilizes rapidly, even without agitation

28 MCHM concentration (mg/l) VOLATILIZATION MCHM volatilization measured under quiescent conditions Half-life = ~4 days Significant for long timescales (impoundments) Time (hours)

29 MCHM concentration (mg/l) VOLATILIZATION Henry s law constant for MCHM 6.4 x 10-9 atm L mol -1 Fragment constant estimation method (TOXNET) Predicted volatilization half-life = 51 days! Model Lake Assumption Time (hours)

30 ADSORPTION TO FINES? In both cases, the mysterious disappearance accompanied the introduction of fine coal particles.

31 SITE A DATA: MASS DISTRIBUTION 30% finer than 11 microns 99.9% 100%

32 SITE B DATA: MASS DISTRIBUTION Removes fines from flotation 7% finer than 11 microns 77% 80% finer than 11 microns

33 % Remaining ADSORPTION TO FINES? Lab data also confirms that MCHM sorbs quickly onto coal and tailings. 100% 80% 60% 40% Coal ~50% removed within 5-10 minutes. 20% 0% Tailings Time (min)

34 WHAT ABOUT DESORPTION? Repeated column leaching tests (x8) consistently showed no MCHM in the leachate, even under spiked conditions. Corroborates field testing that shows no MCHM in the environmental discharges.

35 CONCLUSIONS Empirical field data and laboratory testing show that MCHM is likely (and permanently) adsorbing onto the fine coal. Data shows that NO MCHM is present in environmental discharges. Peer reviewed publications have been submitted: He, Y.T. Thomas, A. Noble, and P. Ziemkiewicz. "Investigation of MCHM transport mechanisms and fate: Implications for coal beneficiation." Chemosphere 127 (2015): Noble, A., Y.T. He, and P. Ziemkiewicz. Partitioning Behavior of 4- Methyl Cyclohexane Methanol in Two Appalachian Coal Preparation Plants. International Journal of Coal Preparation and Utilization (in review).

36 FOR MORE INFORMATION PLEASE CONTACT: Aaron Noble, PhD

ELK RIVER CHEMICAL SPILL JANUARY 2014

ELK RIVER CHEMICAL SPILL JANUARY 2014 Paul Ziemkiewicz, PhD Director, West Virginia Water Research Institute 17 Jan 2014 4-METHYLCYCLOHEXANE METHANOL CAS 34885-03-5 MCHM Has a long name No one can pronounce