Cemented products containing waste from mineral processing and bioleaching

The characteristics of cemented products ranging in initial consistency from ‘paste-like’ to ‘flowable’, relevant to paste backfill and backfill with controlled low strength materials (CLSM), respectively, were compared for mixes incorporating waste from pilot scale bioleaching of European refractory gold, copper and copper/nickel sulphide flotation concentrates. Compositional and structural properties were linked to mechanical strength, hydraulic conductivity and hydrolytic stability (leachability) in fabricated laboratory specimens containing sand, pulverised fuel ash, waste and Portland cement in the proportions 70, 15, 10 and 5, respectively, together with variable quantities of water. In some experiments, sand was replaced by flotation tailings.The results showed that mixtures containing 10% of waste with 15.0–37.5% water by mass gave cemented materials with unconfined compressive strength (UCS) in the range 0.4–3.0 MPa after 28 days of hardening, this range encompassing typical paste-fill and CLSM formulations. They also indicated formulations giving maximum UCS and retention of strength at higher water content in the presence of the (finer sized) waste. Hydraulic conductivity (10−7–10−9 m/s) was comparable to commercial CLSM. Chemical analysis indicated low levels of most toxic elements and correspondingly low diffusion leaching, thus reducing requirements for special lining or encapsulation procedures to avoid groundwater contamination. However, chromium leaching, for example, remained an issue, thus indicating a need for further development before regulatory acceptance and deployment in field applications can become feasible.The formulated materials are consistent in principle with a scheme of integrated waste management based on designed combinations of paste (for mine backfill), CLSM (for engineering foundation construction) and mineral bulk (for site landscape/soil restoration). In particular, they facilitate production of different materials for paste backfill and CLSM applications by judicious adjustment of water content.