Individual study: The use of lime wastes to ameliorate iron pyrites acidification on acidic colliery waste undergoing revegetation at Leigh and Coppull, Greater Manchester, England
Gemmell R.P. (1981) The reclamation of acidic colliery spoil. II. The use of lime wastes. Journal of Applied Ecology, 18, 879-887
Lime-based wastes (often available at low cost in industrial areas) were compared with agricultural ground limestone as neutralizing agents for acidic colliery spoil undergoing acidification due to iron pyrites oxidation, in order to promote conditions suitable for plant growth on spoil from two colliery sites in northwest England.
Liming materials: The effects of three materials on pH and growth of sown perennial rye-grass Lolium perenne and white clover Trifolium repens were examined on two different acidic colliery spoils were tested: Leblanc waste (highly alkaline, pH 12.7 containing large amounts of calcium hydroxide and calcium carbonate); dried calcareous slurry (almost entirely calcium carbonate); and agricultural ground limestone (calcium carbonate).
The calcium carbonate equivalents were 86% for dried calcareous slurry, 57% for Leblanc waste and 93% for ground limestone. Two experiments were undertaken:
1) Acidic colliery spoil (pH 2.9, iron pyrites content 0.67%) from Higher Folds, Leigh (National Grid ref. SD 682002) Greater Manchester, was used to test the effects of the liming materials at rates of 10, 20, 50, 100 and 200 t/ha. Phosphorus (P) was applied at 45, 110 or 220 kg/ha (as triple superphosphate) to investigate interactions of the wastes with P. L.perenne or T.repens (sown in 15 cm diameter plastic pots at an equivalent rate of 200 kg/ha), after fertilization with 125 kg/ha N (urea) and 50 kg/ha K (potassium sulphate). The experiment was randomized and carried out in a glasshouse at 16ºC during the spring and summer. Dry matter production was measured at intervals (cutting, drying and weighing herbage samples). Soil samples were taken to determine pH.
2) Spoil of high acid-producing potential was used to investigate the efficiency of the lime wastes under conditions of rapid acidification due to oxidation of high levels of pyrite. Unburnt colliery spoil from Welch Whittle, Coppull (National Grid ref. SD 546135), pH of 2.5, containing up to 4% iron pyrites was treated with the three lime materials at 10, 20, 40, 60 and 100 t/ha. Phosphorus was applied at 45 and 90 kg/ha P. The pots were sown with L.perenne at 200 kg/ha and fertilized and maintained in the glasshouse as above.
Particle size: To investigate any effect of particle size, Welch Whittle spoil was treated with different particle sizes (<150 µm, <300 µm, <600 µm, <1200 µm or <2400 µm) of Leblanc waste and ground limestone at 20, 50 or 100 t/ha. Phosphorus was applied at 45 and 90 kg/ha followed by seeding and fertilization as described.
Initially, dried calcareous slurry was slightly better than ground limestone in raising spoil pH and promoting growth of L. perenne. Suppression of growth of T.repens at high liming rates was also less evident
Leblanc waste neutralized acidity and promoted plant growth but was less effective than ground limestone. There was evidence of growth inhibition related to the presence of hydroxide at very high application rates.
The pH and growth effects of ground limestone were reduced by increasing particle size (presumably to slower breakdown of particles) at rates up to 50 t/ha, whereas particle size difference did not affect the action of Leblanc waste.
Conclusions: There would appear to be no ecological disadvantages and several economic advantages of using the lime wastes trialed in this study in reclamation of acidic colliery spoils. They were fairly effective at neutralizing the spoils, thus enhancing conditions for plant growth.