Many mines are moving towards conventional paste backfill because it allows a higher extraction ratio, reduces dilution and aids in pillar recovery. Paste backfill improves stability and reduces the risk of rockbursting while providing a means of disposing of waste rock and mill tailings, thereby minimizing surface disturbance.
Cellular Paste Backfill is a high density cellular grout backfill material containing 50% -70% solids obtained from whole mine tailings, cement powders (Portland cements, slag cements, blast furnace cements and pozzolans), water and preformed cellular foam. As well, Cellular Paste backfill mixes can be designed using waste by products such as abandoned mine tailings, pond tailings, bottom ash, remediated soils and aluminum salt cake. Cellular foam is a biodegradable high strength micro bubble produced by combining Magna Foam Concentrate, water and high pressure air in a foam generator.
The addition of cellular foam to a paste backfill mix design has many advantages:
With the addition of cellular foam to a high percentage solids mix, viscosity is greatly enhanced. The resistance to movement between the different layers of the mixture of water, aggregate (tailings) and cement is dramatically reduced. The yield stress of cellular paste mixes is closer to zero before flow begins and factors such as pulp density, grain size, mineralogy and grain shape become less of an issue to the successful pumping of the backfill over distance. Generally, cellular paste backfill mix designs exhibit slumps in the 8-10" range and can resist segregation at higher velocity pumping.
Reduced Moisture Content
Conventional paste backfill mixes contain up to 25% water as a percentage of solids, but with the addition of cellular foam with its ability to break the surface tension of the fines, less water is required in order to make the mixes pumpable. By reducing the water content, the water/cement ratio of the mix is decreased and as a consequence, the Unconfined Compressive Strength (UCS) increases thus allowing for the use of less cement. Strengths from 2 MPa - 7 MPa are achievable depending on grain sizing, void ratio and moisture content.
Adding cellular foam to the paste mix can reduce the density of the mix by as much as 30%-40%. Reducing pulp density by even a fraction dramatically decreases line pressure and greatly improves pumpability. Much longer pumping distances can be achieved. Cellular foam micro bubbles evenly disperse throughout the matrix and produce a more uniform graded fill which reduces terminal settling velocity.
Cellular Paste backfill, because of its lower cement content when compared to conventional paste backfills, is very cost effective. By expanding backfill volume by as much as 25% with inexpensive foam and reducing the problems associated with pumping conventional backfill mixes long distances, Cellular Paste Backfill allows for higher extraction ratios without adding large cost to expanding existing backfill production equipment. With the addition of a simple low cost foam generator system from CCT to the existing mine batch and pumping equipment, very large cost reductions can be realized.
Call Cellcrete Technologies Inc. for further information.