Advanced Slurry Sampling and Elemental Analysis Solutions

Integrating sampling and analysis into one product is the best solution. Placing the analyzer within the sampler ensures the probe sees a large volume of sample and provides dedicated real-time measurement, time aligned with shift composite and calibration samples, with negligible bias. On the plant design and CAPEX front, this approach reduces piping design hours and expenditure on pumps. On an ongoing basis, integration minimizes maintenance and operation costs. The Thermo Scientific AnStat-430 Sampling and Analysis Station encapsulates this approach. As a low head-loss system, it offers market-leading availability and is well-matched to short residence time applications requiring high frequency dedicated measurement.

Thermo Scientific samplers and analyzers have the lowest head loss on the market. This helps minimize the need for additional piping and sample pumps. Our solutions can help reduce capital costs of new plant construction by requiring very low elevation and using gravity instead of pumping.

If the critical streams are monitored frequently operators should be able to control the plant to achieve overall stability and best metallurgical results at minimum cost. The less critical intermediate streams can then be monitored at a lower frequency for the fine tuning of the circuit.

The degree of confidence required in the assay-based control decisions and the rate of change in the process must be known. Streams that are more critical for control of the plant need to be monitored more frequently. Trends in plant performance will then be shown in more detail, showing effect of feed grade changes or control actions on grade in real-time and giving greater confidence in control decisions. For example, in a base metal concentrator, the main objective might be to adjust target tails based on varying feed grade while producing a particular concentrate grade in the cleaners. Dedicated online sampling and analysis with AnStat-430 stations on the rougher feed, final tails and final concentrate, coupled with an MSA-430 Multiplexed analyzer on intermediate streams such as rougher concentrate and in the cleaner circuit, provides a balance of capital cost with optimized assay update frequency to achieve good control of plant processes.

Yes, and it could be significant. First, let's assume that all streams are analyzed as intended. Cycling around each stream takes time and the frequency of measurement is therefore lower than with a dedicated analyzer. Each additional stream means a longer time between measurements. For some applications where the typical rate of process variation is slower, this isn't a problem; a measurement every 13 minutes may be sufficient (12-stream MSA). Budget constraints may also be a factor. However, for greater process control and benefit from real-time continuous measurement, the Thermo Scientific AnStat-430 Sampling and Analysis Station combines representative sampling and elemental analysis into one product. A second challenge comes from routing several streams to a single location. In a sizeable plant, this often involves  pumping sampled slurry through long sections of pipes, creating risks such as pipe blockage or pump failure. Besides the capital cost of the pumps and sample lines, there is an ongoing maintenance cost. Analyzers measuring 20 streams could be reduced to 4 or 5 of the most important streams after only a few months of operation because of the reduced availability of each sample line from blockages. Slurry density and viscosity often makes it difficult to transport and sample representatively. Using dedicated AnStat analyzers on critical streams and then strategically placing multi-stream analyzers to measure between 3 and 12 streams typically provides a good balance between cost, analysis intervals, and uptime.

To fully monitor the recirculating load, it is also necessary to monitor the rougher and scavenger concentrates and cleaner tailing streams. As recirculating loads tend to build up slowly with time, these analyses are not required on a minute-by-minute basis so these streams can be monitored with a lower cost-per-stream centralized analyzer.

If the critical streams are monitored frequently, operators should be able to control the plant to obtain overall stability and best metallurgical results at minimum cost. The less critical intermediate streams can then be monitored at a lower frequency for fine tuning of the circuit.

The degree of confidence required in the assay-based control decisions must be known. Streams that are more critical for control of the plant or where the rate of change is faster need to be monitored more frequently. Trends in plant performance will then be shown in more detail, showing effect of control actions on grade in real-time and giving greater confidence in control decisions. For example, in a base metal concentrator, the main objective might be to minimize metal losses in primary flotation while producing a particular concentrate grade in the cleaners. In addition, test work may show that recirculating loads tend to build up in the cleaning stages, which is a result of recovery of excessive gangue in the rougher concentrate. Continuous analysis of tailings grades provides a critical tool in the operation of rougher flotation. On-line analysis of concentrates provides a tool to manage grade-recovery in the cleaners and to better control impurities to meet the smelter requirements.

The elements to be analyzed are determined by the objectives of the process control strategy and the particular metallurgical problems which are anticipated from prior metallurgical test work. The frequency of analysis required, often referred to as the assay update time, depends on the following criteria:

• The fluctuation in assays in a given process stream considering the residence times of the processes immediately upstream
• The stability of the circuit

At a minimum, the assay update times of the analyzers for the critical streams should be less than half of the retention time of the preceding process stage.

Therefore, in the tailings stream from a scavenger bank of cells with a retention time of five minutes, the grade can be expected to vary considerably in two minutes during upset conditions or reactions to process control actions, so on-line analysis should be made at an interval less than this to provide the best visibility of real-time plant performance. To obtain these sorts of assay update times, dedicated AnStat-430 analyzers are best, or a centralized MSA-430 analyzer with a small number of streams located nearby the process sample points.

Before selecting an online slurry analysis system, consider if light elements will need to be measured and if the measurement technique is amenable, given the expected variation in mineralogical and particle size for the process. In addition, look at the streams to be measured and ask these questions:

• What streams are critical for control of process (this usually includes Feed, Final Tail, and Concentrate)?
• Is there a need for understanding trends within the process (usually includes Rougher Concentrate and Cleaner Tails)?
• What are the elements to be measured in each stream that process control decisions will be made upon?

Based on this information, the various trade-offs taking into account all factors between centralized and dedicated analyzers, Prompt Gamma Neutron Activation Analysis (PGNAA) and X-ray fluorescence (XRF), capital and maintenance cost, etc., can be worked out and a recommendation made for the optimum system configuration for the particular plant.

For example, in a nickel concentrator, it is essential to control the concentration of talc (or MgO) in the concentrate stream. To be able to control the concentration of talc in the concentrate, measurement of Ni and talc in each of the feeds, rougher concentrate, and final concentrate streams is needed so that the appropriate concentration gradients between these can be optimized and the ratio of Ni/talc can be maximized at each stage for minimum reagent usage. It may also be useful to measure Fe and S in the feed stream because this may give an indication of the nickel mineralogy entering the plant. In all other streams, it is only necessary to measure Ni because the information from these streams is used only for monitoring the recovery of Ni. Thus, an analyzer using PGNAA measurement technique would be required with multiplexing for the three main streams, and a multi-stream analyzer using XRF technology for the other streams.

The AnStat-430 system provides the highest integrity sampling and analysis, so this is the best choice. Sometimes budgets or space limitations mean a centralized multiplexed analyser such as MSA-430 analyzer is more suitable. 

For any stream that requires highest integrity sampling but whose flowrates are too high for the MSA tanks, use a Thermo Scientific SamStat-30C Representative Slurry Sampling Station as the primary sampler that feeds the MSA. The sample integrity is retained in the shift composite sample taken at the MSA and in the slurry seen by the MSA probe for online analysis.  

If only a shift composite sample is required and online assays are not, then a SamStat-30 station is the ideal sampling solution with highest integrity to support your metallurgical balance.