The products of this reaction are water (H₂0) plus the salts: sodium chloride NaCl) or calcium chloride (CaCl₂). To those less familiar with chemistry, the term "salt" is generally thought of as NaCl (table salt), however, a "salt" should be thought of as the product of an acid-base reaction. When an acid is in a water solution it dissociates into a cation (H⁺) and an anion (Cl^-). The term pH refers to the concentration of hydrogen ions (H⁺). As these ions are combined with the (OH^-) from the base, the number of hydrogen ions (H⁺) decrease which results in the neutralization of the acid. The pH of a solution can range from 0 to 14. A pH of 7.0 is considered to be completely neutral (deionized water). So a solution that is acidic has a pH of less than 7.0 and a solution that is basic has a pH above 7.0. Lime is a strong base and an excess of lime can quickly produce a pH above 12. It can also be seen, as shown in the reactions above, that a molecule of calcium hydroxide (Ca(OH)₂) will react with twice (2x) as many molecules of hydrochloric acid (HCl) than sodium hydroxide (NaOH) does.

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The molecular weight of quicklime, CaO is 56 and that of hydrated lime, Ca(OH)₂ is 74.
(Calcium, Ca=40, Oxygen, O=16 and Hydrogen, H=1)

The best way to think of "molecular weight" is a "weight ratio". Once quicklime is added to water it converts to hydrated lime so you are essentially comparing the same product in different forms. In the simplest form 56 lbs of quicklime is equivalent to 74 lbs of hydrated lime. Another way to view this is to take your current hydrated lime usage (tons) and multiply it by 0.757 to come up with the approximate usage of quicklime equivalent to your hydrated lime usage. This factor comes from dividing the molecular weight of quicklime (56) by that of hydrated lime (74), which equals 0.757, or 75.7%.

Whether or not it is practical to switch from using bulk hydrated lime to using quicklime generally depends upon the amount of lime you're using and your willingness to purchase a slaker. (Slakers insure that you have complete, intimate mixing/reacting of water with the quicklime, which is very important since the reaction is exothermic and produces steam). If you're currently using bulk hydrated lime you already have a storage silo so purchasing a silo won't be an issue unless you want to increase your storage capacity. If you're producing a lime slurry it's likely that you'll require a slaker rather than the current mixer you've been using. As a general rule bulk hydrate seems to be used for requirements of up to 1-2 trucks a month (300 to 600 tons/year, a truck holds approximately 25 tons). Some customers will use quicklime if they're using only 100-200 tons/year, but generally quicklime is not considered until somewhere in the 300-600 tons/year range. In any case, the costs vs. savings factors need to be carefully evaluated prior to making the decision to switch from bulk hydrated lime to quicklime, and each customer's requirements will be different.

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BAGGED: If your are a distributor of hydrated lime you will almost always require only bagged hydrated lime. If you are a lime user, and require a sizeable amount of lime, but have to transport it to multiple locations (such as individual well sites, etc.) your only option is probably hydrated lime in bags. Generally, customers who are currently using bagged hydrated lime in their process do not require a lot of lime. In some cases bagged hydrated lime has an advantage because each bag is 50 lbs which allows it to be used in batch preparations where a certain number of bags of hydrated lime are added to the mix/batch. Advantages: You only require storage space and a mixing tank to prepare the slurry. Disadvantages: the price (bagged hydrated lime is more expensive), the unloading (pallets of lime have to be removed from the truck by a forklift) and the handling (each bag has to be handled by a worker).

BULK: Bulk hydrated lime is usually used by customers who have a higher usage requirement. Your longterm projected usage of hydrated lime needs to be taken into account in considering bulk hydrated lime. If the usage is expected to increase, it may pay to invest in the capital equipment to use bulk hydrated lime right at the start. Some customers, who are in the process of implementing a new lime slurry operation, will start with bagged hydrated lime, then switch to bulk once the operation gets going. Advantages: the price (bulk hydrated lime costs less than bagged hydrated lime), the unloading (the lime is delivered via a pneumatic tank truck which blows the product into the silo, so the customer has no labor in unloading), and the handling (the lime is automatically handled from the silo to the slurry preparation). Disadvantages: Initial capital investment (you will require a lime silo, feeder and metering equipment to control the feed of the hydrated lime to the mixing tank).

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Limestone: Although limestone is often referred to as "lime" it is actually a "stone or rock", either naturally occurring in mineral deposits or, when physically processed, in various size pebbles, crushed, ground or pulverized. The term limestone generally refers to calcium carbonate, CaCO₃ and magnesium carbonate, MgCO₃, which are usually found together, to some degree, in various proportions. The term Dolomitic Limestone general refers to limestone deposits with a much higher percentage of MgCO₃ than is found in high calcium limestone deposits. (Cheney Lime & Cement Company produces quicklime, CaO from the calcination of deposits of high calcium limestone in Shelby County, AL. This quality of limestone is required to produce the high calcium quicklime and high calcium hydrated lime products we supply.)

Lime: In the correct use of the term, lime is actually a "chemical" which is in the form of calcium oxide, CaO (quicklime) and/or magnesium oxide, MgO which is produced from the high temperature process of calcination which takes place in a lime kiln. Lime also refers to calcium hydroxide, Ca(OH)₂ and magnesium hydroxide, Mg(OH)₂ which are the hydroxides produced from the reaction of the oxide and water. In the case of calcium oxide, CaO the reaction occurs readily and is highly exothermic. Both Ca(OH)₂ and Mg(OH)₂ are chemical bases.

Aglime: Generally, Aglime (sometimes referred to as Agstone) is a dolomitic or high calcium limestone that is finely ground to enable it to neutralize soils that are acidic. Although limestone is considered relatively inert, it can be attacked by a strong acid, or a weak acid over time, and will neutralize the acid. If the acidity is quite high, then either quicklime or hydrated lime is usually used.

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1. The assumption is that increasing the market share will always provide the best price. This works to a point, however, when a cooperative begins to get too large the number of lime suppliers able to supply the high volume decreases, thus competition is actually reduced. Eventually, a cooperative can reach a point where only one lime supplier can supply them, which leaves them in a somewhat vulnerable position.

2. All price increase projections for the year have to be given to all of the members at the same time. When cooperative members (especially municipalities) are bidding individually throughout the year a lime supplier has the opportunity to "sharpen their pencil" on the next bid, if they lose the current bid. When bidding on a cooperative, the approach is "all or none", consequently, a lime supplier has to factor in any potential price increases and lock them in for a year.

3. Large cooperatives tend to discourage the introduction of new lime competitors because all of the business is "locked up". If a potential lime supplier does enter the market and is able to win the cooperative bid, they have no assurance that they will have the bid the next year, even if there are optional extensions to the contract.

Generally, moderately sized market share cooperatives appear to successfully gain pricing advantages and do not seriously deter competition. Extremely large cooperatives, on the other hand, appear to offset the cooperative advantages by deterring competition and the introduction of new lime competitors.

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Contract Extensions: Municipalities, and some industries, will provide for annual extensions, sometimes up to three years, if both parties are in agreement. The general assumption is that holding the price for another year is always good for the organization. This is not always the case. In some instances, a lime company has recently lost a contract and needs to replace that lost tonnage. In those cases they may bid more competitively to replace the lost business. Also, the prices in the lime market do follow cyclical patterns as a result of changes in the economy, as well as the introduction of new kilns. Those industries and municipalities, who have nearly automatic contract extensions, often miss out when the market price does decline.

Multiple Year Contracts: When considering the duration of a lime contract it's often appealing to try to lock in a price for two or three years, with limited escalations in price being allowed on an annual basis. In addition to the price advantages, the purchasing department reduces the number of RFQs (request for quotes) that it has to be involved with. The lime user feels that they've locked in a supply of lime at a predictable price, however, what often happens is that the lime users, with the three year contract, are "out of the loop", with regard to market changes. Since they tend to become identified with a particular lime supplier they may find themselves removed from the "active prospects" list of other lime companies, which indirectly tends to reduce competition. Some companies, who have two and three year contracts, may also find themselves in a difficult situation in a tight lime market since a lime company is less interested in helping out a lime user who offers little or no opportunity for future business.

Recommendation: Whenever possible, an annual (twelve month) time frame will often provide the best contract period for many businesses. The lime user will be monitoring the market for lime, at least on an annual basis, and the current lime supplier will always have to "be on their toes" with regard to price, service and the lime market. Most successful lime users want to make certain they're paying a fair price for their lime to insure that they have good, dependable suppliers. If an option for multiple years is needed it's generally best to have annual extensions, subject to approval by both parties. This allows the lime user to avoid multiple years of a high priced lime in a declining market, and allows the lime supplier to limit their exposure to a low price in a rising market. The downside to an annual contract is that it does require that the purchasing department monitor the price of lime more frequently.

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Acid Normality and Sample Size: In the case of the ASTM C25 test, a 1.000 N HCl is used, which results in a requirement of exactly 2.804 grams of the sample of calcium oxide (CaO). In the case of the AWWA B202 test, 0.1782 N HCl acid is required and the sample must be exactly 0.500 grams. (The acid solution for the AWWA B202 test is usually prepared by the lab personnel since a commercial, standard solution at 0.1782 N is not readily available.) Care must always be taken in preparing any standard solution to insure that it is as accurate as possible since an incorrect acid normality will result in inaccurate CaO% determinations. Both the purchased and prepared standard solutions should be periodically checked to insure that they are accurate.

Generalized Test Procedure: The laboratory steps in the two tests are very similar. The sample of quicklime (CaO-Calcium Oxide) is pulverized, then the desired weight is measured into a flask which contains a specified amount of water. The flask is placed on a hot plate and a specified amount of additional boiling water is added. The flask is swirled and boiled for a minute, then removed from the hotplate. The flask is placed in a cold water bath to cool it to room temperature. (The solubility of lime is inversely proportional to temperature.) Sugar is added, then the flask is swirled and allowed to stand for 15 minutes, with periodic additional swirling to allow the sugar and lime reaction to take place. Phenolphthalein solution is added as an indicator, and the sample is titrated until the first disappearance of the pink color that lasts for at least three seconds. The burette is then read to determine the available calcium oxide percentage. (CaO%).

Modified Procedures: Are these test procedures ever modified by lime users and producers? The answer is yes, however, the only thing that is usually changed is the sample size and/or the normality of the acid. The lab procedures, including the addition of sugar to increase the solubility of calcium hydroxide, are not changed. Keep in mind that both the ASTM C25 and AWWA B202 tests are designed to enable the lab personnel to read the available lime percentage from the burette. The drawback to this is that the sample must be weighed to a very specific weight. All forms of quicklime (pebble, granular or pulverized) immediately begin to undergo air slaking when exposed to any moisture in the air. This simply means that the moisture in the air reacts with the quicklime to form calcium hydroxide. This process occurs all the time, but has its greatest effect when the sample has been pulverized to a powder. The surface area of the quicklime is increased dramatically, which increases the rate of air slaking. Weighing the sample to a very specific, designated weight requires the lab personnel to take extra time in weighing, during which air slaking of the sample is occurring. Dependent upon the extra time required, the sample weight can change. Care should always be taken to insure the sample is weighed as quickly as possible. To minimize air slaking, a sample can be weighed exactly, at a weight close to the "targeted weight", then titrated with a commercially available, standard solution. The lab test procedures will be the same, however the available lime (CaO% ) will need to be determined by calculation, using the amount of acid used and the exact weight of the sample. Lime users and producers will often modify the test in this way since it will generally produce more accurate results, however, you do lose the convenience of simply reading the available lime percentage (CaO%) as the milliliters of acid used.

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The solubility of calcium hydroxide in water is quite low, with a range of 0.185 grams per 100 grams saturated solution at 0^o C to 0.071 grams at 100^o C. (Note that the solubility decreases with an increase in temperature.) As the sample is stirred, a suspension of calcium hydroxide is maintained (milk of lime). As you titrate the calcium hydroxide in solution, more will dissolve. Since most of the calcium hydroxide exists as a solid in suspension, it cannot be titrated until it has dissolved (gone into solution.) The titration process itself involves a reaction of the acid with calcium hydroxide in solution and will consume lime, allowing more lime to go into solution. However, this process can be speeded up significantly by the addition of sugar. When sugar is added, an intermediate product is formed, calcium sucrate (calcium hydroxide saccharate) which is significantly more soluble than calcium hydroxide. For example; the addition of 35 grams of sugar will increase the solubility of the calcium hydroxide from 0.159 to 13.332 grams per 100 grams of saturated solution at 25^oC; which is a solubility factor increase of 84.

What happens if you don't add the sugar as prescribed in the test? The acid has to be added relatively slowly to allow the calcium hydroxide that is still in suspension as a solid, to dissolve as calcium hydroxide that is in solution is neutralized. The titration procedure requires that you add acid until the first disappearance of color that lasts for three seconds. If you've inadvertently added too much acid you've effectively created a chemical "buffer". With excess acid introduced, the phenolphthalein pink color will disappear, and the excess acid will react with any calcium hydroxide going into solution with the result that the disappearance of color can persist for three seconds, indicating an incorrect end to the titration. The amount of acid used may be determined to be less than it should be and the resultant calculation (or reading from the burette) will indicate an available lime percent lower than the true value.

A number of companies titrate the calcium hydroxide without adding sugar and are comfortable with this. The addition of sugar in the standard test procedure was developed to insure that the endpoint of the titration could be reached as quickly and accurately as possible, thus providing the greatest accuracy in the available lime determination. Those industries who currently do not add sugar in the test for available lime, and who have processes that can be significantly affected by fluctuations in the available lime determinations, may want to consider the addition of sugar to their testing procedure. Both ASTM and AWWA provide very detailed procedures and equipment requirements for testing both quicklime and hydrated lime. Please contact them directly for their industry recogized and accepted standard test procedures: (ASTM C25 - AWWA B202.)

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When obtaining a sample of hydrated lime the sample should also be sealed, primarily to keep the sample clean and free of debris. The hydrated lime does not react with moisture in the air since it has already been converted from quicklime to hydrated lime. Over an extended period of time, however, the hydrated lime (calcium hydroxide) will react with carbon dioxide in the air to form calcium carbonate. As a general rule then, all lime samples, whether quicklime or hydrated lime, should be in sealed containers.

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What happens is that, although the quicklime (calcium oxide) on the surface of the pebble converts to calcium hydroxide (hydrated lime), the excess water can absorb the heat generated in the reaction and result in a delay in the hydration process. In addition, the calcium hydroxide on the surface, because of it's limited solubility in water, will tend to block the exposure of additional water to the quicklime within the pebble, resulting in a delay or cessation of the hydration reaction. Quite often, the "drowned" quicklime will be removed from the slaker as "grit", which will later undergo hydration in the grit pile. To avoid "drowning the quicklime" it is important to operate the slaker at both the correct water to lime ratio, and at the optimum water temperature. A lime user who notices an increase in the amount of grit, which appears to react later in the grit pile, may find that they're experiencing the phenomenon of "drowning" the quicklime.

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Note: Included in the table above are the molecular weights for both quicklime and hydrated lime. Hydrated lime is produced from quicklime by a reaction with water. Using the molecular weights as a ratio, 56.08 tons of calcium oxide will react with 18.01 tons of water (molecular weight) to produce 74.09 tons of hydrated lime. The ratio of calcium oxide to calcium hydroxide is 1:1.32, so a truck of quicklime is equivalent to 1.32 trucks of hydrated lime. This information is useful in determining the cost benefits of quicklime vs. hydrated lime, and whether the savings warrant going to quicklime.

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An unusually Low CaO% may indicate air slaking: A theoretically pure quicklime, CaO (56 lbs.) will react with water H₂O (18 lbs.) to produce calcium hydroxide, Ca(OH)₂ (74 lbs.). If the sample were absolutely pure quicklime, then the available CaO% would be 100%. If the same sample were to be completely air slaked, then the available lime would ideally be 75.7% (56/74). Percent readings near this range can be an indication that the sample may have become air slaked. A sample taken should be sealed, and tested relatively soon to avoid issues of air slaking. Also, once a sample is pulverized for testing, the sample is very prone to air slaking so the weighing of the sample should be completed quickly to avoid air slaking. Air slaking adds weight (water chemically reacts with quicklime) to the sample, and steadily causes a reduction in the available lime CaO% values.

If the available lime percent readings are unusually out of line with what you normally receive a re-test is advised. To be sure the sample is not the issue you will want to obtain another sample from the truck or railcar, underneath the surface, otherwise you find that you are just be re-testing a compromised sample. Also, it's important to be certain that the acid used in the titration is correct. Because these are prepared locally, it's important to make sure that an error has not occurred.

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The "Rapid Sugar Test" for available lime, either the ASTM C-25 or AWWA B202 version, is usually the chemical test that is used to determine the available lime in a sample of quicklime or hydrated lime. In a theoretically pure sample of quicklime, devoid of all naturally occurring impurities, and with an unrestricted time period to convert the limestone to quicklime with heat, you would have an ideal available lime of 100%. The available lime percentages generally experienced in the commercial market for high calcium quicklime typically require a minimum of either 90% or 92%, depending on the industry. Most lime companies have available lime values higher than 92%.

In the reaction to convert quicklime to hydrated lime; CaO + H₂O --> Ca(OH)₂ you are essentially doing the equivalent of taking 56.08 lbs of CaO (mw-molecular weight) and 18.00 lbs of water (mw), and reacting them to produce 74.08 lbs. (mw) of calcium hydroxide. Based upon the purity of the sample, an approximate comparison can be made between the available CaO% of the quicklime and the expected CaO% equivalent in the hydrated lime. It can be seen from the chart below that the highest CaO equivalent possible in a 100% pure sample of calcium hydroxide would be 75.7%.

Determination of Solubility of Quicklime in Water: Since quicklime calcium oxide (CaO) cannot exist in water in the oxide form, the solubility of CaO in water is based on the calcium oxide equivalent of CaO in Ca(OH)₂. The values for the solubility of CaO in water, shown in the chart above, represent the amount of CaO that is within the dissolved Ca(OH)₂. The calculation for the ratio of CaO in Ca(OH)₂ appears below:

There are two factors that come into play with regard to the "effective charge" of the Ca⁺² and Mg⁺² ions:

(1) Although both calcium and magnesium ions have a +2 charge, the distance from the ionic extremity (border) to the +2 charge at the nucleus is different. In the case of magnesium, the size (radius) of the ion is smaller (0.66 Anstrom units) than that of calcium (0.99 Anstrom units). The increase in the size of the calcium ion is due to the addition of another energy level. Consequently, the distance from the +2 charge to the extremity of the ion in the magnesium ion is shorter by about 33% then the distance in calcium. The shorter distance means that the electrostatic attraction between the magnesium ion (+2) and the oxygen ion (-2) is stronger than that of the bond between the calcium ion (+2) and the oxygen ion (-2). Note that, in both cases, the +2 charge offsets the -2 charge and results in the neutral compounds of CaO and MgO. However, the inherent elemental differences (number of protons and electrons) between the elements of calcium and magnesium, result in a difference in their ease of ionization (removal of electrons) and their ability to chemically combine (strength of their electrostatic forces) with other elements and compounds in reactions.

(2) Also, in the case of the calcium ion, even though the charge is the same as that of magnesium, the +2 charge at the nucleus of the calcium ion has to go through more electrons, eighteen (-18), compared to the magnesium ion which has a +2 charge, but only has to go through ten (-10) electrons. This reduces the overall attraction (strength) that the calcium ion (+2) has for other elements and chemical groups as compared to magnesium.

Effects on Solubility: Because of this effectively "weaker" +2 charge, the solubility of calcium hydroxide is greater than magnesium hydroxide. The water molecules clustering around the calcium hydroxide compound have enough force (Van der Waals force) to dissociate the compound into a calcium (+2) ion and two hydroxyl (-1) ions, although not to a great degree, which accounts for the limited solubility of calcium hydroxide in water. In the case of magnesium hydroxide, the attraction of the magnesium +2 ion and the hydroxyl -1 ion is too great for the water molecules to overcome, and the magnesium hydroxide remains mostly out of solution.

The difference between calcium and magnesium can be readily seen on the Periodic Table of Elements. Although calcium is just below magnesium vertically, there are six elements between them horizontally. Nature does favor calcium carbonate and magnesium carbonate occurring together, so even deposits of high calcium limestone will have some magnesium carbonate mixed in, which is considered a "naturally occuring impurity."

For comparative purposes, Mg(OH)₂ has a solubility of 0.0042 grams per saturated solution, which can be considered insoluble in water. Furthermore, the reaction of MgO with water is not highly exothermic, so MgO will stay in water as "grit". CaO, however, will quickly convert to the hydrated lime form in a dramatic exothermic reaction. MgO can be forced to react more quickly with increased pressures and temperatures. For reference, a partial Periodic Table of Elements appears below:

For comparative purposes, Mg(OH)₂ has a solubility of 0.0042 grams per saturated solution, which can be considered insoluble in water. Furthermore, the reaction of MgO with water is not highly exothermic, so MgO will stay in water as "grit". CaO, however, will quickly convert to the hydrated lime form in a dramatic exothermic reaction. MgO can be forced to react more quickly with increased pressures and temperatures.

The Preference Criterion refers to a code designating the degree to which the products are coming from the country of origin. In the case of quicklime and hydrated lime from Cheney Lime & Cement Company, all of the components are USA based, so the designation would be "C". More specifically, from the NAFTA Certificate of Origin Instructions, a Preference Criteria "C" refers to "The good is produced entirely in the territory of one or more of the NAFTA countries exclusively from originating materials."

Slaked Lime: In the description of calcium hydroxide products in the HS Tariff Classification System, it can be a bit confusing. In one instance it will refer to calcium hydroxide as "hydrated lime", then another time as "slaked lime". Hydrated lime produced from calined limestone (quicklime) can be thought of as simply a reaction of the quicklime (calcium oxide, CaO) with the exact amount of water (H₂0) to produce a dry hydrated lime (calcium hydroxide, Ca(OH)₂). The term "slaked lime" refers to the reaction of quicklime with water to a dry powder, as well as the addition of excess water to produce a paste, slurry or milk of lime. Technically then, dry hydrated lime is also considered to be slaked lime.

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Fahrenheit - The Fahrenheit temperature scale is based upon 32 ^oF as the freezing point of water and 212 ^oF as the boiling point of water. (The Fahrenheit scale was devised by Gabriel Daniel Fahrenheit (1686-1736), a natural philosopher who invented the mercury thermometer in 1714.)

Celsius (Centigrade) - The Celsius (Centigrade) temperature scale is based upon 0 ^oC as the freezing point of water and 100 ^oC as the boiling point of water. The formulas to convert between Fahrenheit and Celsius (Centigrade) come from the fact that there are 180 degrees (212-32) between freezing and boiling in the Fahrenheit temperature scale, so each degree in the Fahrenheit scale is equal to 100/180 (or 5/9) of the Celsius/Centigrade scale. (The Celsius scale was devised in 1742 by Anders Celsius (1701-1744), a Swedish professor of astronomy.)

Kelvin - The Kelvin temperature scale is based upon the physics of cooling a gas and represents an extrapolation of the Centigrade temperature scale to -273 ^oC (or more accurately, -273.15 ^oC) at which point there is no longer any motion of atoms or molecules; or put in the simplest way, "there is no heat". This point in the Kelvin temperature scale is assigned a value of 0^oK. For the Celsius (Centrigrade) temperature scale the freezing point of water would be 273^oK and the boiling point would be 373^oK. (The Kelvin temperature scale was developed by Lord Kelvin (1824-1907), a British physicist.)

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"Effect on Metals. When in contact with metal equipment, lime does not affect steel or cast iron to the slightest extend. In fact, by coating these metals with a lime whitewash, it acts as a conservation agent by protecting the metals from oxidation. However, any form of lime or strong alkalin will disastrously attack and destroy aluminum, except special alkaline resistant alloys of this metal. Lead and and brass are also readily attacked, and under some circumstances lime will literally dissolve lead."

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Best Quicklime Size: In some situations the size is very clearly defined and the plant designer has no option. Usually this involves the major classifications of pebble and granular quicklime. However, within the sizes of medium and rice size pebble quicklime, the plant designer has options to consider. From a product availability standpoint the best design choice is to make certain that the plant can run either medium or rice quicklime, and if possible also granular. This is especially important if there is a high demand for quicklime, whether on a continuous or emergency basis. The following paragraph explains this further.

Product Availability Factor: The cost of quicklime is very freight intensive, so quicklime is usually considered a regional product. Because of this all of the quicklime used at a specific plant comes from a relatively close geographical area. Whether that area has one producer, or multiple producers, all of the quicklime has to be processed through kilns. In most lime production areas there are often multiple kilns in production. During processing, the quicklime is crushed and screened to generate the various sizes. If the available pebble quicklime sizes in an area were evenly split between medium and rice, and your plant can only use medium, your available supply of quicklime from producers would only be half of what is actually produced. If you require a granular size quicklime the situation becomes even more difficult since this is considered to be a minor size in the lime market.

Recommendation: It is recommended that a new plant be designed to at least be able to run either medium or rice. The plant may not be able to alternate between truckloads of the medium and rice sizes, but in the event of a lime shortage, the plant would be able to switch sizes. It is not recommended that a granular size be used for a high volume user, unless this size is mandatory for the process, since this could severely limit product availability, especially during peak demand periods.

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Truck Delivery: A truck can generally be considered to hold about 25-30 tons of quicklime. The minimum freight weight requirements are usually 25 tons for quicklime (50,000 lbs) and 22 tons for bulk hydrated lime (44,000 lbs); bulk hydrated lime is lighter than quicklime. A weight of 25 tons/truck is useful to use as a general guideline since it will cover most shipments. Generally, you are allowed one to two hours for unloading a truck before a demurrage charge is applied, based upon the individual carrier's policy. Depending upon your demand for lime, any silo you design should be able to hold no less than 2 trucks of lime (50 tons). If a truck is ordered when the silo gets to the point where it can hold a full truck, you avoid problems associated with demurrage. This is quite a small silo, so it is recommended that, dependent upon your requirements, you have a silo that can hold 4-5 trucks (100-125 tons) of lime. The additional silo capacity will give you an added buffer in the event of unforeseen truck delivery problems.

Rail Delivery: A railcar can generally be considered to hold about 100 tons of lime. In our market area bulk hydrated lime is usually not shipped in rail cars aside from PD cars (Pressure Differential cars), which are owned by the lime user or lime supplier. Usually the railroad will allow you two days to unload a railcar. Depending upon your demand for lime, the silo should be able to hold no less than 1-1/2 rail cars of lime (150 tons). Rail delivery times are not as specific as truck, so it's important to consider having additional silo capacity. A silo with 250 tons will enable you to unload two cars into a silo when less than 50 tons are remaining in the silo. Although your lime demands may dictate your silo requirements, a silo with 500 tons capacity would enable you to have an added buffer for unforeseen rail delivery problems. (i.e. a rail car enroute is set aside for a day to be repaired, etc.)

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One other very important point to be careful of involves the density used in the calculation of silo size. The term "lime" refers to both quicklime/calcium oxide and hydrated lime/calcium hydroxide, however the density of the two materials are significantly different. Generally, quicklime is shipped as "pebble quicklime" whereas hydrated lime is a fine, white powder similar in consistency to "flour". It's important to be sure to know exactly which product will be going into the silo. Some lime users have used the density of quicklime in their calculations when they were actually going to be using bulk hydrated lime. The result is a silo which will not hold a full truck of hydrated lime.

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1. Charge per mile to and from the site of the silo.
2. Charge to clean the truck before and after handling the lime.
3. Cost per hour for the actual operation.

Here are two companies we are aware of that can provide this type of service:
(1) Bulkmatic Transport, at Jacksonville, FL, 904-783-3500, Mobile, AL, 251-694-0900, and (2) Fenn-Vac, Inc, at North Charleston, SC, 843-552-8306. For pricing and availability of equipment please contact these companies directly. If either of these companies are not able to provide this service in your area, they should be able to direct you to a company near you. (Other companies that can provide the service of removing dry lime from a silo may contact us at sales@cheneylime.com. We would be pleased to include their name and phone numbers here as a service to our customers and other lime users.)

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