Turbidity Mitigation in an Oil Sands End Pit Lake through pH Reduction and Fresh Water Addition

• Author / Creator

  Brandon, Jordan T

• The remediation of oil sands wastes such as fluid fine tailings (FFT) and oil sands process-affected water (OSPW) are of increasing concern in the oil sands industry. End pit lakes are one remediation option currently being researched at commercial scale in Base Mine Lake (BML) operated by Syncrude Canada Ltd. BML contains a bottom layer of FFT, averaging 45 m, and a top layer of OSPW and fresh water with a depth of 8.5 m in 2014. BML has experienced high turbidity in the water layer throughout its lifetime, hindering sunlight penetration into the lake which is essential to the development of a healthy ecosystem that in turn drives the remediation of FFT and OSPW. Two research questions were studied during this series of experiments: (1) Can lowering the pH increase water clarity and (2) how does water composition affect water clarity. Addition of 500 L to 4000 L of CO2 to the water layer of a 160 L column lowered the pH from 8 to 6 with no initial improvement in Secchi disk depth (0.2 m) in 80% OSPW (20% fresh water), 60% OSPW (40% fresh water) and 20% OSPW (80% fresh water). The addition of HCl in 80% OSPW lowered the pH from 6 to 3.5 and resulted in an increase in water clarity as measured by Secchi disk depth from 0.2 m to 0.8 m within five days. A secondary improvement was seen between 30 and 60 days with Secchi depth improving from 0.8 m to 1.6 m. This time lag was unexpected and mirrored in 60% OSPW with CO2 addition. Secchi depth improved in 60% OSPW from 0.2 m to 1.2 m between day 78 and day 113 with no significant improvement before day 78. 60% OSPW (Control) without CO2 addition and 20% OSPW with CO2 addition did not show an improvement in water clarity in the same time frame. The reason the time lag is present in not readily apparent but may be due to the reaction kinetics of the dissolution of CaCO3 and the cation exchange on suspended clay particles. iii Turbidity was reduced in 60% OSPW (300 NTU to 10 NTU), 60% OSPW (Control) (300 NTU to 57 NTU) and 20% OSPW (200 NTU to 57 NTU). Turbidity of 23 NTU corresponded to Secchi depth of 1.2 m in 60% OSPW, exceeding the goal of 1 m and indicating sufficient water clarity for the development of a healthy ecosystem. Decreasing the pH is a possible way to increase water clarity but is affected by the ionic strength of the water layer. Experiments on 2 L columns over three months with 90% OSPW, 81% OSPW, 54% OSPW, 36% OSPW, 18% OSPW, 5% OSPW and 100% BCR and no pH adjustment resulted in no discernible effect of water composition on water clarity. Only 5% OSPW showed turbidity values (24 NTU) similar to the 23 NTU indicated as sufficient for water clarity. No pattern was found relating water composition to final turbidity. The relationship between light penetration depth (0.01 light intensity) and Secchi depth was also explored and yielded an experimental equation of light penetration depth = 1.45 * Secchi depth + 0.1.

• Subjects / Keywords

  • Oil Sands
  • Turbidity
  • FFT
  • OSPW
  • PH
  • End Pit Lake

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ST7F72D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.