Nature of Ore Solids & Solids as the Product

The nature of solids, with respect to adjusting their separation velocity with chemical additives, has much to do with surface charge and the features defined by Stoke’s Law. Particles have mixed charge sites but are, with few exceptions, naturally, net anionic. Sand mining and processing uses a lot of these polymeric materials to improve capture, to remove them from streams to save pumping and processing equipment, and to improve the final product quality. The basic polymers fall into two categories: coagulants and flocculants.

Coagulants – Designed to neutralize repulsive charge sites on particles to be removed or captured. These are industrially dominated by cationic polymers like poly diallyl dimethyl ammonium chloride (pDADMAC) and others like Epichlorohydrin. pDADMAC coagulants are of relatively low molecular weight, 50,000 and up, and often with 100% charge density, although copolymers with acrylamide monomer can be used to dilute the charge.

Flocculants – Designed to bridge particles based on physical and electrochemical interaction. The polymers are high to very high molecular from 1,000,000 and up.  Most are polymers of acrylamide with charges varying between cationic (to 100% charge density), nonionic and anionic (to 50% charge density).

Sand is surprising…

Our image of sand is that it is non-reactive rock – just rock that will readily settle in a water tank. While that is more or less true of larger particles of sand, upon first removal from the soil, sand contains large amounts of fine particulate and often clays and other problematic contaminants. Understanding the surface characteristics and the actual composition of the sand and the contaminants, would be quite helpful in selecting a polymeric treatment program to control and capture the desired solids: the sand.

Sand is a mixture of quartz with “contaminants” which include iron and aluminum that can impart positive charge spots to the surface. Often the assumption in treating for sand settling is that a standard cationic coagulant plus anionic flocculant program is the correct pathway in polymer program development. That mistake is expected based on the general experience in coagulation and flocculation of suspended solids. However, the composition of the sand will affect how the polymers absorb onto the particle surface based on the electrochemical interactivity with the existing charge sites. Charge neutralization of the particle surface is often a function of absorption or reaction with the positive charge sites on the sand, presented by the metal contaminants, rather than the more prevalent anionic charge sites. The interactivity goes beyond neutralization of the surface charge to the creation of a cationic site that will attract other net negative particles.

While the actual composition of the sand would be very beneficial to know, often those data are made superfluous by what is learned in a comprehensive jar testing program. What is a comprehensive jar testing program?

Proper Jar TestingPolymer Charge Density Graph

The proper procedure for conducting jar testing, to select the best performing polymer, at the best performing dosage rate is a matter of discipline and logic. Discipline is the foundation of selecting the best program. The best program is often more than is required, but in mining, the polymer usage rates are (very high) such that disciplined, comprehensive testing is nearly always warranted.

Logic

The chart shows the 3 basic axes that need to be tested and selected:

  1. Charge
  2. Charge Density
  3. Molecular Weight

After the best polymer based on these criteria is identified, then further testing is required to determine the optimum feed rate. In large applications, where a lot of polymer is required, competitiveness can mean differences of a tenth of a ppm, a 55% charge density instead of a 50%. Expertise at jar testing is mandatory.

Discipline

Below is a basic decision tree that, if followed, will lead the reader to the best polymer for a given application. In difficult applications, where the chart does not lead to a solution or the solution is too expensive, a corporate, polymer expert should be engaged – true experts run jar tests hundreds of times per year and will find the best treatment option.

Here is a basic decision process in doing jar testing; how to select the best polymer for a given application.

Polymer Program Development Logic

Real solutions developed by PureLine are designed beyond the logic framework and are tailored to meet client’s unique needs. Fill out our Contact Form below or call PureLine at (847) 963-8465 to connect with a PureLine expert to identify the most effective polymer for you! The best polymer options are not included in the chart but remain a matter to be left to polymer experts like those at PureLine.

 

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