Hydrate Membrane Technology

Hydrate membrane (HM) technology is a cost effective solution for removal of suspended solids (down to 2 microns) from tailings.

Dewatering Challenges

Dewatering of tailings is a major technical challenge for the mining industry. Tailings contain fine suspensions that do not settle under gravity and may resist settling under flocculation. Miners use thickeners and flocculation as well as cyclones and belt presses to reclaim some water, while pumping remaining watery tailings into tailings storage facilities where tailings can be impounded for decades. Current filtration technologies are currently limited in use due to their high cost and low efficiency.

Hydrate Membrane Technology

The hydrate membrane technology is a gel-based membrane filtration system for simple removal of suspended solids (down to 2 microns) from tailings. The HM filter is 35 to 67% cheaper than the current common technologies used to dewater thickener underflow (belt press filters and solid bowl centrifuges). The HM filter works well at low pressures, with optimum flux rate at about 10 psig but acceptable flux rate at zero pressure. The hydrate membrane gel also spreads out easily against a retaining fabric, making it easy to deploy. The hydrate membrane produces very low turbidity water. Use of the HM filter will enable miners to:

• produce much lower turbidity water,
• recycle more water,
• reduce their water use,
• pre-treat water prior to reverse osmosis (if they want to use RO to remove dissolved metals and salts etc),
• reduce their tailings storage facility size and risk,
• prevent turbid water entering ground water, and
• open the incepted solids up for further processing and resource extraction.

The HM technology was created and patented by University of Queensland scientists working on novel technologies to improve filtration. The technology has been successfully tested in the lab on metal and coal tailings and at a coal mine site on coal tailings. Two peer-reviewed journal papers have been published on its efficacy in respected journals of Scientific Reports (Malekizadeh and Schenk, 2017) and Minerals Engineering (Liu et al, 2018).

Uses of Hydrate Membrane Technology

An automatic filtering device has been developed which filters the tailings while clearing the filter cake. The primary target for use is in the filtration of existing tailing storage facilities to enable low cost rehabilitation and closure. A secondary target will be in the production process in tandem with or replacement of existing thickening and flocculation processes. An effective way of meeting environmental for water total suspended solids discharge requirements. A successful demonstration test was conducted in mid-2017 on thickener underflow from a CHPP in Queensland producing very clear water from thickened tailings between 5 and 15% solid.

Example Applications

The HM filter can be deployed to dewater tailings from a thickener underflow to make the tailings suitable for dry stacking or reprocessing. The HM filter can be deployed in a trench with walls lined with concrete, holding a tray of the HM, with a floor of impermeable plastic. Water is piped into the tray to filter through the membrane and then pumped away from the bottom of the trench. The tray is cleared periodically of filtrate by a clearing arm or a grader. A 12 m2 trench should handle 10t/h of thickener underflow at 850 LMH. The HM filter has a variety of uses including dewatering old open cut pits, seepage ponds, and sump dams.

Performance

The HM filter performs well against belt press filters and solid bowl centrifuges across a range of cost and water quality criteria.
Table of comparative dewatering costs

Note: Costs have been compared using the methodology in ACARP C14012 (published 2004) based on common 2004 costs.

• Compared to a belt press filter or solid bowl centrifuge, the HM filter should deliver:
• Lower moisture filtrate, which is lighter to transport and more suitable for reprocessing or pit disposal;
• Greater water recovery;
• Greater plant availability/reliability given the near-absence of moving parts; and
• Lower turbidity water (NTU = 0 to 12).

References: Malekizadeh, A, Schenk, P.M., 2017. High flux water purification using aluminium hydroxide hydrate gels. Scientific Reports 7, 17437 Website Link: https://www.nature.com/articles/s41598-017-17741-z D. Liu, M. Edraki, A. Malekizadeh, P.M. Schenk, L. Berry, Introducing the hydrate gel membrane technology for filtration of mine tailings 2018. Submitted to Minerals Engineering and under minor revision.