Hydroseparation

The commercially available hydroseparators (HS) (HS-01, HS-02, HS-11, HS-21) were invented to process solid water-insoluble powdered samples to produce representative “heavy-mineral concentrates” of particles that follow Stokes’ law when settling in a carefully controlled upward pulsating water stream. Ideally, to be applicable for HS, powdered particles should have densities between 3 and 20 g/cm3 and grain sizes of less than 0.3 mm, including industrial flotation size fractions (-45 µm).

All above mentioned devices, which are covered by several Russian and one international patent, may be described as consisting of two separate parts: a Water Flow Regulator (WFR) and a Glass Separation Tube (GST). The WFR, when connected to a standard municipal water supply (ca 3 atm) and switched on, modulates the water flow according to different regimes that are experimentally determined by working on many different size fractions produced from samples of different origin and type. These regimes are dependent on the efficiency of the hydroseparation process (monitored visually under a binocular microscope) and are controlled by a series of buttons on the front panel of the WFR (for HS-01, HS-02 and HS-02M), or by an operating software designed for a PC (in the case of the HS-11) to archive the best efficiency of separation.

The hydroseparation process moves the light fraction upwards in the GST with water, eventually collecting a vessel (beaker) under the GST. The heavy concentrate collects inside the GST at its base. Different sizes of GST are used for separation, depending on the grain-size and the required productivity of processing/amount of the loaded sample. Also, the latest design of GST, supplied together with the HS-11 and patented separately (Russian patent application #2004135890), is equipped with a moving valve placed in the horizontal knee of GST. This invention allows better separation and higher productivity for a wider range of size fractions of the powdered samples.

The usual criteria for successful separation by means of laboratory-scale HS devices (HS-01, 02, 11) apply with respect to representative sample size and number. In general, the weight of the primary sample is principally a function of the overall homogeneity of the sampled material and the abundance and grain size of the "heavy" minerals to be determined. Typical samples weigh in the range from 10g to 2kg. Naturally, one should be guided by experience to decide how much material should be used for hydroseparation. However, from the authors' experience with the technique, it is necessary to have from 100 to 300 g of each size fraction (especially for the finest fractions, as they are the most informative to work with). The final concentrate of 5 to 20 mg is produced from preliminary concentrates after processing of standard aliquots of about 100g. Such aliquots are processed part by part by loading into the GST in the form of a water suspension and portions of pre-concentrates are collected in another vessel under the GST. The GST is suspended over a wide tray to avoid any loss of material that can be returned to the GST, if needed.

In addition, one has to know that, in general, any powdered sample that has been immersed in water and then dried may no longer be suitable for HS because of the clustering effect caused by oxidization of and reaction between particles. To avoid these problems, treated fractions should always be kept under water once they have been HS-processed in case they have to be combined with other portions to be treated by HS again. However, if this somehow has occurred or the primary sample shows signs of easily floated particles, an antiflocculant (e.g., a few drops of acetone, KMnO4, or detergent) may be added to a suspension and/or the sample may also be treated by ultrasound.

The separation productivity using HS-01 and HS-02 models will vary with the operator and the nature of the particles, whereas the new generation of hydroseparators, represented so far by the latest laboratory version (HS-11 model) and the semi-industrial hydroseparation module HS-21, are less operator-dependent.

In the case of the HS-11, its operation is controlled by a software that results in separation controlled by an automated regime. This device makes it possible to perform the separation using the same small aliquots of about 20-50 g for each loading, as for the HS-02 model. However, good productivity (for a laboratory separator) is achieved here by automated repetition of separation regimes (once calibrated) and set up for a particular sample. In addition to the database of existing standard regimes worked out for fixed ranges of particle sizes and petrologic description of the sample, it is possible for the operator to program the device on a sample by sample basis and to archive the optimal regimes for specific samples types, adding them to the existing database. This option makes it easier for the beginner to operate the device and obtain representative concentrates for each processing stage. Once the first portion of the sample is processed, the real productivity of separation by means of the HS-11 is calculated by the same software. It is obvious that problems of contamination of separation products during HS-processing will always depend on the care of the operator because loading the suspension into the GST, collection of concentrate in one vessel, washing of the tubing of the device in between separation sessions/samples will always be present. However, the operator will now be more relaxed since he/she controls all possible sources of contamination by the fixed/automatically documented order of separation operations. This was not possible when using earlier versions of laboratory hydroseparators (HS-01 and HS-02 models).



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