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Several popular languages including Haskell and Python use the indentation and layout of code as an essential part of their syntax. In the past, implementations of these languages used ad hoc techniques to implement layout. Recent work has shown that a simple extension to context-free grammars can replace these ad hoc techniques and provide both formal foundations and efficient parsing algorithms for indentation sensitivity. However, that previous work is limited to bottom-up, LR(k) parsing, and many combinator-based parsing frameworks including Parsec use top-down algorithms that are outside its scope. This paper remedies this by showing how to add indentation sensitivity to parsing frameworks like Parsec. It explores both the formal semantics of and efficient algorithms for indentation sensitivity. It derives a Parsec-based library for indentation-sensitive parsing and presents benchmarks on a real-world language that show its efficiency and practicality. © 2014 ACM.

Several popular languages including Haskell and Python use the indentation and layout of code as an essential part of their syntax. In the past, implementations of these languages used ad hoc techniques to implement layout. Recent work has shown that a simple extension to context-free grammars can replace these ad hoc techniques and provide both formal foundations and efficient parsing algorithms for indentation sensitivity. However, that previous work is limited to bottom-up, LR(k) parsing, and many combinator-based parsing frameworks including Parsec use top-down algorithms that are outside its scope. This paper remedies this by showing how to add indentation sensitivity to parsing frameworks like Parsec. It explores both the formal semantics of and efficient algorithms for indentation sensitivity. It derives a Parsec-based library for indentation-sensitive parsing and presents benchmarks on a real-world language that show its efficiency and practicality. © 2014 ACM.

The Kell process is cyanide-free, and eliminates emissions of sulphur dioxide, arsenic trioxide, and other toxic species often emitted by smelters and roasters. It comprises four sequential steps: aqueous pressure oxidation, atmospheric leaching, heat treatment, and atmospheric oxidative leaching. Tests on a range of concentrates, including PGMs, refractory gold-silver, copper-gold, and polymetallic concentrates have given extraction efficiencies of over 95%. When compared with smelter-refining, Kell shows economic benefits (capex 18-33% of smelting, opex 51-66%, electricity consumption 13-46%) and environmental benefits (greenhouse gas emissions 57-61% of smelting, acidification 5-27%, human toxicity 37-62%, and freshwater ecotoxicity 43-55% of smelting). Synergies for Kell plants alongside smelter-refineries include utilisation of recovered acid from sulphur abatement systems and excess capacity in precious metal refineries. Kell is unconstrained by concentrate grade and impurities, allowing the co-location of Kell plants for treatment of non-smeltable concentrates alongside existing smelters. Kell has been demonstrated in a nine-week integrated pilot campaign at a 110 000 t/a plant treating a UG2-Merensky concentrate at the Pilanesberg platinum mine in South Africa. A centralised PGM concentrate processing plant using the Kell process is also being planning in Zimbabwe., The Kell process is cyanide-free, and eliminates emissions of sulphur dioxide, arsenic trioxide, and other toxic species often emitted by smelters and roasters. It comprises four sequential steps: aqueous pressure oxidation, atmospheric leaching, heat treatment, and atmospheric oxidative leaching. Tests on a range of concentrates, including PGMs, refractory gold-silver, copper-gold, and polymetallic concentrates have given extraction efficiencies of over 95%. When compared with smelter-refining, Kell shows economic benefits (capex 18-33% of smelting, opex 51-66%, electricity consumption 13-46%) and environmental benefits (greenhouse gas emissions 57-61% of smelting, acidification 5-27%, human toxicity 37-62%, and freshwater ecotoxicity 43-55% of smelting). Synergies for Kell plants alongside smelter-refineries include utilisation of recovered acid from sulphur abatement systems and excess capacity in precious metal refineries. Kell is unconstrained by concentrate grade and impurities, allowing the co-location of Kell plants for treatment of non-smeltable concentrates alongside existing smelters. Kell has been demonstrated in a nine-week integrated pilot campaign at a 110 000 t/a plant treating a UG2-Merensky concentrate at the Pilanesberg platinum mine in South Africa. A centralised PGM concentrate processing plant using the Kell process is also being planning in Zimbabwe.

Approaches to the piloting and scale-up of oxidative and pressure leaching are presented, with particular emphasis on scale-up ratios, using examples from many projects. For pressure leach flowsheets, the duration of the pilot runs is critically important in proving the integrated process. For well-proven processes applied to typical feed materials, such as pressure oxidation of auriferous sulphide concentrates, around 100 hours of piloting may be sufficient. For novel flowsheets or atypical feed mineralogies or process waters, pilot runs of 1 000 to 2 000 hours may be necessary. Piloting of a process may be limited by the facilities of testing laboratories, therefore demonstration-scale testing of innovative flowsheets may be necessary, and specific large-scale testing of units for the scale-up of equipment is routine., Approaches to the piloting and scale-up of oxidative and pressure leaching are presented, with particular emphasis on scale-up ratios, using examples from many projects. For pressure leach flowsheets, the duration of the pilot runs is critically important in proving the integrated process. For well-proven processes applied to typical feed materials, such as pressure oxidation of auriferous sulphide concentrates, around 100 hours of piloting may be sufficient. For novel flowsheets or atypical feed mineralogies or process waters, pilot runs of 1 000 to 2 000 hours may be necessary. Piloting of a process may be limited by the facilities of testing laboratories, therefore demonstration-scale testing of innovative flowsheets may be necessary, and specific large-scale testing of units for the scale-up of equipment is routine.

Carbonaceous material, including abraded activated carbon, amorhous carbon and graphite, was concentrated by HCl and HF leaching, the mineralogy quantified by X-ray diffraction and elemental analysis, individual grains identified by optical microscopy and analysed by microprobe. Samples from four filter-plant residues showed negligible gold loading on 25 amorphous and graphitic particles averaging 78 micrometres in diameter, 92% analysing less than 90 g/t Au, while 43 abraded carbon particles averaging 87 micrometres, from seven CIP plant residues, had small loadings with 80% analysing less than 90 g/t Au. The effect might be due to most carbon abrasino occurring with freshly reintroduced carbon: an experiment whosed that contact transfer of adsorbed gold between loaded fine carbon and unloaded coarse carbon occurred rapidly, with 50% of Au transferred within 1 h. The results indicate that, for the residues studies, the loss of gold on abraded carbon from CIP adsorption circuits is probably relatively small., Carbonaceous material, including abraded activated carbon, amorhous carbon and graphite, was concentrated by HCl and HF leaching, the mineralogy quantified by X-ray diffraction and elemental analysis, individual grains identified by optical microscopy and analysed by microprobe. Samples from four filter-plant residues showed negligible gold loading on 25 amorphous and graphitic particles averaging 78 micrometres in diameter, 92% analysing less than 90 g/t Au, while 43 abraded carbon particles averaging 87 micrometres, from seven CIP plant residues, had small loadings with 80% analysing less than 90 g/t Au. The effect might be due to most carbon abrasino occurring with freshly reintroduced carbon: an experiment whosed that contact transfer of adsorbed gold between loaded fine carbon and unloaded coarse carbon occurred rapidly, with 50% of Au transferred within 1 h. The results indicate that, for the residues studies, the loss of gold on abraded carbon from CIP adsorption circuits is probably relatively small.

The conditions under which copper-iron-cyanide precipitates may form, particularly in gold plant process and detoxification liquors, were examined. Ammonia and pH were found to have a great effect on the extent of precipitation. The compounds formed were mainly Cu2Fe(CN)6.7H2O and a range of NH3-bearing variants. The long-term stability of the precipitates is important from an environmental perspective: copper ferrocyanide stability may be a problem in tailings dams under alkaline conditions and in the presence of some free cyanide. The importance of copper in detoxification processes is illustrated using data from cyanide detoxification tests with the Inco SO2/air process at Gosowong gold mine and with hydrogen peroxide detoxification at Kanowna Belle gold mine., The conditions under which copper-iron-cyanide precipitates may form, particularly in gold plant process and detoxification liquors, were examined. Ammonia and pH were found to have a great effect on the extent of precipitation. The compounds formed were mainly Cu2Fe(CN)6.7H2O and a range of NH3-bearing variants. The long-term stability of the precipitates is important from an environmental perspective: copper ferrocyanide stability may be a problem in tailings dams under alkaline conditions and in the presence of some free cyanide. The importance of copper in detoxification processes is illustrated using data from cyanide detoxification tests with the Inco SO2/air process at Gosowong gold mine and with hydrogen peroxide detoxification at Kanowna Belle gold mine.