Modern Quarrying October-November 2015

brick failed and the force measured at failure was documented. The compressive strengths obtained were then averaged. The mixture ratio that gave the highest compressive strength was subsequently employed to manufacture bricks for water absorption, weight loss, and leaching rate tests. Unconfined compressive tests were also done on commercial bricks to provide a basis for comparison. Water absorption rate and weight loss tests: Two solutions with different pH values, one acidic and one neutral, were used for these tests. The tailings bricks were first prepared from mixture 7 ( Table II ) and cured in water for 24 hours. Tests were con- ducted on four samples in each solution. The bricks were immersed in water baths, one containing water at pH 7 and the other an acidic solution at pH 4. The solid–to-liquid ratio was maintained at 15. The saturated weight of the bricks (Ws) was measured every 24 hours over a five day period. After five days, the bricks were dried at 110°C for 24 hours and the oven-dried weight (Wd) recorded. The bricks were again tested for compressive strength. The percentage water absorption rate was then calculated as:

COMPLETE SIZING SOLUTIONS For over 35 years, MMD have been at the forefront of Mineral Sizing and In-Pit Sizing & Conveying solutions, providing systems that maximise production, improve safety, and increase efficiencies. The Twin Shaft Mineral Sizer™ handles over 75 different minerals in more than 60 countries worldwide, with the

Water absorption (%) = [(Ws - Wd]/Wd × 100

The weight loss tests were done in the neutral environment only (pH 7). The average weight loss was measured after the bricks had been soaked in neutral water for seven days then dried overnight at 110°C.

Different mixtures used in brickmaking

Mixture number

Tailings (kg)

Cement (kg)

Water (ℓ)

1 2 3 4 5 6 7 8

2

1 2 6 8 5 3

0,6

14

2,65

9 7

3,0 2,5 2,5 2,5 3,3

10 12

5

10

ability to process both wet sticky material or hard dry rock or a combination of both through the same machine.

10

5

3

Table II: Different mixtures used in brickmaking.

MMD offer local support via its network of MMD offices. Contact us

Results and discussion Particle size distribution:

Figure 1 shows the particle size distribution of the material used in the brickmaking process. The results are presented in cumulative form, in which the total amount of all sizes retained or passed by a single notional sieve is given for the range of sizes. The results indicate that most of the particles fell into 90–200 μm range. 80% of the material passed the 200 μm screen aperture while about 12% passed the 90 μm screen. The particle size range used in standard commercial brickmaking includes coarser sand particles as well as fine particles. The material used in these tests was, in com- parison, relatively fine. A cost analysis study done by Roy et al., (2007) showed that cement-tailings bricks are generally uneconomical compared to the soil-tailings based bricks, therefore future test work will have to consider the addition of coarse particles, possibly from mining overburden.

to discuss your project with one of our experts.

+27 11 608 4801 sizers@mmdafrica.co.za www.mmdsizers.com

MMD Africa Half Page Advert 260 x 90mm.indd 1

6/8/2015 9:17:03 AM

29

MODERN QUARRYING

October - November 2015