Issue 11, p. 446 (2022)

  Poster

ISO 8685 compliant contractual ship-loading export facility: bauxite sampling plant process design and equipment selection for chemical sampling

  • W. P. Slabbert  
  • M. Nyokong

The paper discusses the process design and mass balance for the minimum and maximum design case to illustrate the ISO 8685 compliance of a 2-year-running barge loading payment station sampling plant. The plant samples -100 mm, export quality, bauxite material from a barge-loading conveyor delivering 10 kton/h at 5.4 m/s. The green field operation does not know the Coefficient of Variation or the Size Range Factor as required inputs to calculate the Number of Primary Increments and Minimum Gross Sample Mass required. Therefore, informed assumptions were made given performance data of a neighboring sampling system that is in operation for over a decade. Without the available variation and size factor data the ISO-compliant scheme design could not commence. Where this data is not available for green field projects, it poses a risk that plant designs may not be compliant where variabilities could exceed assumptions on the input parameters.

The system is designed for various barge carrying capacities with lot size in mass. Operational quality assurance however requires samples more frequently and therefore sublot periods are 4 hourly time based. ISO 8685 compliance is achieved with sample increments taken at maximum throughputs and barge sizes to determine the time-based interval. At reduced throughputs, the fixed time interval regime results in the minimum ISO requirements to be exceeded and tied in well with client overall quality incentives.

Primary sample increments from a tailored cross belt sampler are crushed automatically in the sampling plant to 25 mm and then to 6mm using two stages of double roll crushers. The sample is then subdivided through secondary and tertiary sampling to produce a composite 4-hourly chemical sample. The 4-hourly sublot samples are collected in an ergonomic 4-way carousel with each composite sample representing 1-hour barge loading production — allowing the client quality assurance insights into their blending facility performance.

Keywords: ISO 8685 compliant, sampling plant, mass-based lot, time-based sampling interval

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