People wanted a bit more about blended tailings and waste rock, so here we go.

According to the GARD Guide, if your material is at least 85% saturated, then the oxygen diffusion rate should be so low that acid mine drainage should not be an issue.  For this reason, you don’t want to have “dry” tailings.  In my limited experimentation, you need to have a pretty wet filter cake in order to make maximum compaction achievable.  How wet will depend on your specific materials.  I only ran demonstration Proctor tests on proxy samples of tailings and various types of gravel at various mixing blends. 

Also, researchers have been using an idealized blend, where the tailings just perfectly fill the voids in the waste rock.  No more and no less.  In reality, you will have to accept (and plan for) imperfect blends, while still targeting that ideal blend.  You will have to tolerate some air voids and sometimes you can’t get all rock-to-rock contacts.  There will be excess tailings, and they will separate the rock particles.  Plan for it.  Design for it. 

The theoretically idea blend ratio of four parts waste rock to one part tailings, where you have beautiful rock-to-rock contact, and the tailings just fills the voids works really well with really common stripping ratios of 4:1.  But, this stripping ratio is not a constant number through the life of the mine.  Tailings are often produced at a more-or-less constant rate, although that rate is likely to increase over time.  However, waste rock production can be highly variable.  So, you have to commit to using waste rock that has been placed in a storage facility, until it is needed. 

Will you need to compact your blended tailings and waste rock?  That depends.  It depends on it’s propensity to liquefaction, whether you need to compact it to remove air voids and whether it’s needed to satisfy slope stability requirements.  Sorry I don’t have all the answers.  Sometimes just knowing what questions to ask is a good beginning.

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