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

This blog is Part 3 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.  Part 2 covered the importance of including customer references and whether to use concentration or specific gravity on slurry specifications.  In this post we will discuss the type of raw material that should be used and the importance of dedicated tankers.

 4. Raw material used to make lime slurry

All limes are not created equal.  It is important to know the differences between the raw materials that produce calcium hydroxide lime slurry.  Lime is mined from quarries as calcium carbonate rock.  The rocks are heated to 2500 degrees Fahrenheit in coal or gas fired kennels which burns off carbon dioxide.  The kennels produce calcium oxide (CaO) which is called pebble lime, quicklime, rice lime, or slake lime.  The calcium oxide can be pulverized into difference size pebbles and varies in quality.  The quality of the calcium oxide is measured by calculating the percent of pure calcium oxide available per pound.  Calcium oxide is the cheapest lime on the market because it requires less processing prior to delivery.

To produce hydrated lime, the lime manufacturer will add approximately 20% water by mass to calcium oxide partially hydrating the product without making a liquid slurry.  When water is added the calcium oxide converts to calcium hydroxide.  The calcium hydroxide can be sold in dry form, or further processed (ex: grinding/air separating to reduce particle size) to increase quality or meet specific chemical requirements.

The quality of the raw product should be specified on your bid.  Lime quality substantially impacts the level of  “processing” operators will have to conduct at the water plant.  For example, CAL~FLO slurry is made with air-classified hydrate.  Currently, it is the highest grade raw product that lime mines produce.  The reason is that after hydration, air is blown through a separator and light-weight lime particles that float are collected.  The heavier inert particles, sand, grit, and rocks (seen in picture) are left behind. CAL~FLO further cleans the hydrate in our manufacturing process to produce one of the highest quality slurry’s on the market.

Inert gravel and sand that is produced from a small sample of quicklime.

Your municipal bid documents should specify a high-calcium, air-separated/classified, hydrated lime as the raw material for the lime slurry delivered.  Why pay for a product that requires your water plant operators take out the grit and gravel left from less processed lime instead of running a water plant?  Why pay for a cheap lime when almost 20% of its contents is inert and unusable material?  When you bid out lime slurry for water treatment, you want your plant operators to have the highest quality product with the lowest impact on your maintenance budget.  Some purchasing agents are tempted to take the lowest price of quick lime slurry and mistakenly believe that they can reduce cost.  However,by doing so the purchasing agent is trades chemical cost for additional processing cost including more labor, more maintenance, more equipment, and more replacement costs.

hydrated lime systems

Dry lime feed system with little control and high maintenance costs.

5. Designated Tankers

It seems obvious…  People who deliver product to water plants should be extremely concerned with the chemicals that are stored in delivery tanks.  Common sense would require a clients supplier slurry supplier to ensure the delivery tank would be designated to hold on that chemical or chemicals safe for drinking water, especially in post-treatment applications.  However, we all know the axiom that common sense is not so common.  In the specifications you should ask for your supplier to designate a tanker specifically for lime slurry.  Why is it important?  Read this article on chemical deliver to water plants.  Now, you may not live in Africa and you may not think that cyanide will ever be delivered to the water plant.  However, what is very possible is that other chemicals are hauled in the tanker before it reaches the water plant and then washed and reloaded.  If the tank wash process is not thorough or does not fully clean all the residual chemicals from the tanker you could have traces of some very harmful chemicals going into the water supply.  Why not eliminate that problem by including a designated tanker into the bid specs.

Once we had load of raw lime that arrived and due to our manufacturing process we noticed the slurry did not meet our specifications and had very odd characteristics. We immediately contacted the supplier who denied any changes at the plant or any problems.  We sent the load back and did not deliver the product.  We also cut off shipments from that lime mine.  A month later the supplier came back and let us know that rail cars that had shipped their lime had also shipped corn starch the week before.  They were temporarily delivering these rail cars of lime to a mine while the kennels were being worked on.  The rail cars had not been properly cleaned and the lime was contaminated.  When you mix chemicals in delivery tankers (dry or liquid) bad things can happen.  The question for the individuals who write slurry specs is, “Do you trust your lime slurry provider to get it right every single time if they do not have a designated tanker?”

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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