Coal Preparation

Novel Processing to Reduce Cost of Generating Dry Stackable Tailings

Coal Preparation » Process Control

Published: January 23Project Number: C28073

Get ReportAuthor: Daniel Borrow, Joshua Starrett, Yiyi Liu, Bo Fan, Kaiyuan Qin, San Thang, Kevin Galvin | University of Newcastle

The overall goal of this project was to apply novel polymers to produce dry stackable tailings in the coal industry. Despite an exhaustive investigation, it was not possible to produce the necessary polymer addition regime needed to achieve the goal of a dry stackable tailing. This report outlines in detail the work conducted, and the findings achieved.

Specifically, the objective of this project was to apply novel polymer chemistry to promote more effective solid‐liquid separation of solids from tailings streams. Polymers synthesised through RAFT Polymerisation at Monash University were used in the experimental work. The potential for solids recovery from tailings streams was investigated, firstly using a model clay system, followed by an industrial coal tailings slurry. The purpose of this work was to produce hydrophobic flocs which could then be recovered using either froth flotation or oil agglomeration technologies.

Traditional methods for processing tailings involve the addition of high molecular weight anionic polyacrylamides to promote the formation of large aggregates known as flocs which settle much faster than the primary particles, allowing rapid recovery and hence recycling of most of the process water via the thickener. The thickener underflow is typically at a solid concentration of 25‐35 wt%, hence carries considerable water content to the tailings‐storage facility. The increased volume of tailings raises several issues, including the large footprint for storage, and the loss of water. This was always a high‐risk, high‐return project aimed at using new chemistry to address an old but increasingly significant problem.

This project focused on the use of these novel polymers in order to produce relatively small hydrophobic flocs. Following the flocculation of a variety of feed sources, both model and real tailings streams, the particles were then subjected to froth flotation and oil agglomeration technologies. These technologies, particularly froth flotation, have long been used as a method of hydrophobic particle recovery, while oil agglomeration has successfully been shown to be effective at recovering ultrafine hydrophobic particles.

The performance of the novel polymer binders showed promise in their use as flocculants to deliver increases in settling rate and water clarity, however minimal hydrophobic particle recovery was achieved. In all cases, the yield from froth flotation was negligible. This finding suggests the material following flocculation remained hydrophilic. However, when using a real coal tailings slurry, it was found that a natural level of hydrophobicity was present, perhaps due to the presence of carbonaceous material. Oil agglomeration, using a novel emulsion binder, resulted in a 14 wt% yield prior to polymer addition. However, the yield decreased after the addition of the polymer flocculants and subsequent agglomeration process. This shows that the polymers, despite generally behaving as good flocculants, produced a hydrophilic surface that was unable to be recovered using hydrophobic particle recovery methods.

Despite the unsuccessful attempts in producing hydrophobic flocs, further testing was undertaken as a function of the pH were. Again, froth flotation was unsuccessful in recovering any material, while the agglomeration process led to a yield that decreased as the polymer addition increased.


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