Capping the acid generating rock at a mine site with lime neutralization sludge
could provide several benefits to the final reclamation of the mine site including:

• utilization of the residual lime which is contained in the sludge to
  neutralize the acidic water,
• provide a low cost final disposal area for the sludge on the surface of
  the waste rock and within the void space of the reclaimed mined out
  area, and;
• potentially reduce the ingress of oxygen into the overburden by
  applying an impermeable seal.

Further investigations were considered, however, to provide information on
whether:

• the metal hydroxides in the aged neutralization sludge would
  redissolve; and,
• whether the sludge had any sealing potential to reduce the ingress of
  oxygen.

The investigations completed included:

• chemical, morphological and geotechnical evaluations of the sludge,
• on-site barrel reactors and weathering cells which monitored leachate
  quality and,
• a field test which evaluated the geotechnical laboratory results on
  several sludge applications of different ages on the waste rock.

The investigations completed have provided information on:

• the ability of the sludge to minimize the generation of acid by the
  waste rock when the alkaline sludge is present in significant amounts;
• the insolubility of the metal hydroxide in the lime neutralization
  sludge acid generating waste rock when the alkaline sludge was
  present in significant amounts.
• the geotechnical parameters pertinent to describing the handling
  characteristics of the sludge;
• suggestions and benefits to retaining the sludge near the surface, and;
• the sealing potential of the sludge to reduce or minimize the ingress of
  oxygen when applied either as a cap to the surface of the waste rock
  or “injected” into the waste rock.

The projects were conducted by contractors under the management of NB Goal