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May 3, 2013
5 Essential Recommendations to Ensure Supply of High Quality Lime Slurry (Part 2)

This blog is Part 2 of a 3 part series on how municipalities can write comprehensive specifications which help insure the quality of lime slurry delivered by the chemical supplier.  Part 1 discussed the need for ANSI/NSF 60 certified lime slurry.  In this post we will cover the importance of including customer references and whether to use concentration or specific gravity on slurry specifications.

We really appreciate our customers.  We enjoy serving our customers and work hard to provide process technology that not only exceeds expectations, but solves everyday problems.  We also assume that all other manufacturers have the same integrity and drive.  Sadly some do not.  When companies appear on bid sheets, it is up to the municipality to vet their qualifications and check the quality of their product.  One of the best ways to insure quality bidders is to require references.

2. Require at least 5 customer references

When writing specifications for lime slurry, the specs should require at least 5 references of current customers who have received lime slurry (not liquid caustic, dry lime, or some other chemical) from each bidder.  The municipality should give weighted preference to references in the same locale or state.  If the references provided are not local, the bidder should be asked to explain the availability of supply and how shipping will affect the long term price of the lime slurry.

Each bidder’s references should showcase water plants who share similar characteristics to your plant.  When you contact the references you should ask if the reference is still a customer (if not, why), if the performance of the lime slurry is acceptable, if the lime slurry is consistent with each delivery, if the supplier has maintained consistent pricing, and if the supplier offers outstanding customer service?  Language in the specification should reflect the importance of quality references.  The specifications should have language that states that the bidder can be disqualified by not submitting 5 references or if the references submitted are unacceptable.

3. Slurry Concentration or Specific Gravity

Historically, most water plants specify slurry concentration on chemical bids.  Unfortunately, even though the purchasing department specifies a concentration, operators at the plant seldom check the actual concentration of what is delivered.  There are several reasons why:

  • Operators may not know what concentration that purchasing has specified
  • They may assume the chemical company is delivering the contracted concentration
  • Some operators do not know how to accurately calculate lime slurry concentration using a sample of delivered slurry
  • Operators mistakenly think verification is not required when they have received paperwork from the supplier that lists the lime slurry concentration

One issue in verifying slurry concentration is that certain suppliers use different variables to calculation the slurry concentration.  One new client told us they were purchasing a 35% generic hydrated lime slurry.  After purchasing CAL~FLO they lowered their chemical dosage.  The client was very pleased.  He said that we must make a better slurry.  While in many cases that is true, we tested the concentration from his slurry supplier.  He had been paying for 35% slurry when he was only receiving 24% concentration of slurry.  We delivery a 30% concentrated slurry, so our client did save money, but did not reduce the actual dosage of slurry.  His former chemical supplier knew he did not check the concentration and had been taking advantage of him for many years.

A new approach…

We base our slurry concentration on the fact sheet published by the National Lime Association (NLA).  The NLA is a consortium of the major lime producers in the USA.   The NLA’s fact sheet specifies a 30% hydrated lime slurry will have a specific gravity of about 1.22.  We believe that municipalities should move from using slurry concentration on bids to specific gravity.   Specific gravity is easy to measure.  By using specific gravity the municipality levels the playing field between suppliers.  So when we state that CAL~FLO is 30% and a another chemical provider says they sell a 35%, the real concentration should be based on specific gravity (is it 1.22 ).

Operators can measure the specific gravity of lime slurry samples using several methods described below.  However, the results will only be as accurate as the sample taken.  The sample should not be taken directly from the delivery tanker because lime slurry is a suspension can settle during transportation.  Once the slurry is off loaded into the bulk storage a sample should be taken after the slurry has been adequately mixed.  The operator should know if the slurry in the bulk storage has been diluted and the final concentration of slurry in storage given by the supplier.  After a sample is taken one of the following methods should be used:

  • Graduated Cylindar – the most cost effective approach to measuring the specific gravity of a slurry sample.  This test can be performed with existing lab equipment.  To measure the specific gravity of slurry use the following method:
      1. Pre-weigh a 100 ml graduated cylinder on a scale
        sensitive to 0.1 gram.
      2. Fill the cylinder with exactly 100 ml of well-mixed slurry
        and reweigh.
      3. Subtract the empty graduated cylinder weight from the
        filled weight. Divide the difference by 100 to obtain the
        density in g/ml.
      4. Compare the weight to know NLA standards. (1.22 = 30% / 1.21 = 29% /1.20 = 28% / 1.19 = 27%)
  • Gardco WPG Cup – Very accurate method of measuring specific gravity.  Check out this video describing how to use the cup.  Here is a list of written instructions on how to test using the cup (although the slurry is not necessarily lime slurry in the calculations).
  • Mud Balance – One of the fastest methods to measure specific gravity of slurries and very similar to the Gardco WPG Cup.  For more information on how to use a mud balance check out this video.

In the final post of the series on writing specifications for lime slurry, we will cover types raw materials acceptable for producing high quality lime slurry and why your supplier should use dedicated tankers.

Click this link to learn about our CAL~FLO lime feed equipment.


We would enjoy questions and feed back on this and other blog topics.   Please submit comments through our website or LinkedIn company page.

Author: Dallas Burnett


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Burnett, Inc.     7095 Highway 11      Campobello, SC 29322      1-800-726-4187      (864) 592-1658 tel      (864) 592-1690 fax