Hydrate membrane technology 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 . Miners use thickeners and flocculation as well as cyclones and belt filter presses to reclaim some water, while pumping remaining watery tailings into tailings storage facilities (dams) where tailings can be impounded for decades. Current technologies are currently limited in use due to their high cost and low efficiency. Tailings dams build up until they have trouble storing the tailings without risk.

Hydrate membrane technology The hydrate membrane (HM) technology is a cost effective, 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 filter presses 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 (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, 2019).

Uses 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 reduction in water levels, rehabilitation, and closure. A secondary target will be in the production process in tandem with or replacement of existing thickening and flocculation processes. 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. A video of the demonstration test can be viewed at https://youtu.be/07nxdAf5Bn8.

Example application The HM filter can be used to dewater old open cut pits, seepage ponds, sump dams, etc., and return water for mining operations. The HM filter can also be used 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 filter tank design (see Appendix 1).

Performance The HM filter performs well against belt filter presses and solid bowl centrifuges across a range of cost and water quality criteria. Table of comparative dewatering costs Unit process Capital Operating Total Cake Through- put Savings moisture $,000 $/tonne $/tonne % T/h Hydrate 100 1.3 1.5 26 10 -- membrane Belt filter 350 1.8 2.3 35 17 -35% press Solid bowl 500 3.3 4.6 42 9 -67% Centrifuge Note: Costs have been compared using the methodology in ACARP C14012 (published 2004) based on common 2004 costs. Compared to a belt 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).

Clean&Recover Clean&Recover is dedicated specifically to management of water in the mining industry. We offer products to clean tailings water and to remove heavy metals from acid mine drainage. Luke Berry CEO, Clean&Recover Ph +61 417 077 342 [email protected] Peer-reviewed 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 Liu, D., M. Edraki, A. Malekizadeh, P. M. Schenk and L. Berry (2019) Introducing the hydrate gel membrane technology for filtration of mine tailings. Minerals Engineering 135: 1-8

Appendix 1: Filter tank design The filter tank is based on the design of a standard sedimentation tank used in waste . Water enters at the top through the holes and falls down on to a filter plate (figure 1). The water filters through the hydrate membrane gel on the filter plate (figure 2). As the filter cake builds up, it is scrapped away by a scrapper arm (figure 1). The head pressure of the water on the plate is sufficient without extra pressure or suction to generate a good filtration rate, which keeps the costs of operation low.

Figure 1: Design of the filter tank

Figure 2: Birds eye view of the filter tank

Figure 3: Design of the filter plate

The white HM filter is effective at low pressures A cake that is low in moisture forms on the in removing suspended solids from solutions. HM filter cloth.

The filtered water (left) has a much lower turbidity than the unfiltered water (right).

Technical specifications Hydrate membrane filter specifications Item Specification Flux rate About 360 – 800 LMH depending on pressure and TSS pH tolerance 4-12 Turbidity of filtered water About 7 NTU depending on pressure and TSS Filter cake moisture About 23-30% depending on pressure and TSS Particle filter size 2 nanometres Particles intercepted All hydrophobic suspended solids about 2 nanometres