White chalk powder paint is made up of white pigments, which are mainly calcium and magnesium carbonates, 26.6% mass of white chalk powder is calcium carbonate; the paint has a density of 2.92 gcm-3 and a pH value of 8.9. The concentrations of Ca and Mg differ slightly with Mg having a concentration of 190 mg/g and Ca 100 mg/g. the paint also has some traces of iron of about 1.397 mg/kg. The presence of magnesium suggests that, the limestone used to produce the paint was not pure calcite, but had high amount of magnesium compared to that of calcium. This kind of limestone is dolomitic which has a high concentration of magnesium. The most recommended limestone is the calcite form which has high concentration of calcium. It forms crystalline of high refractive index and brightness. The difference in limestone chemical components is as a result of process of formation and geographical locality. The limestone sample collected from Sultan Hamud Quarry is calcite, because it has higher concentration of calcium. Though the amount of iron is greatly small, there should be no traces of iron, because it forms rust (Fe (OH)3) on dump places. Limestone acts as a source of natural inorganic pigments, that’s CaCO3 and MgCO3 These pigments are naturally found in large deposits on earth crust and manufactured from their ores by grinding, they are mainly known as whiting, chalk ground limestone. They represent the largest group of supplemental pigments of less chemical composition, wide range of particles, and brightness for specific uses. Selected calcite produces a bright and radiant surface. With alkalinity characteristic of pH greater than 8, they offer an antimicrobial protection on surfaces. When applied on surfaces it cures by reaction of CO2 from atmosphere to form a surface with high opacity. This coat rubs off and can be washed off during rainy season. The paint may have other elements such as, Al and Si, which are present as impurities in the raw materials.
1.1 White chalk powder
White chalk is a very low cost type of paint powder, made from calcined limestone (CaCO3) and chalk (whiting). It is white in colour. When slaked with water together with additives it forms a white emulsion (whitewash or lime wash) which is applied on surfaces to form a white film. Chemically white chalk powder may vary greatly depending on limestone used and type of whiting material.
1.2 Background information
White chalk powder is used as a decorative and filler material; it is found normally packed in 10 kg and 50 kg bags. Its main components are quicklime (calcium oxide) and chalk (whiting). Calcium Oxide or quicklime is not found naturally, but it is formed through decomposition of limestone (CaCO3) at a temperature of 900 o C. This result to formation of calcium oxide and CO2 as the products, a process called calcination. In water calcium oxide forms calcium hydroxide which serves as the binder.
Other additives have also been used to improve the intensity and adherence of the whitewash; additives such as; water glass, glue, egg white, Portland cement, salt, soap, flour, earth, are commonly used.
Whitewash is sometimes coloured with soil to achieve colours spanning the range of broken white, cream, yellow and a range of browns. Whitewash cures by carbonation reaction, where by the slaked lime reacts with carbon dioxide in the air to form calcium carbonate crystals.
1.3 History of white chalk paint
For many years the use of traditional lime-based paints was restricted to those involved in the conservation industry, but more recently these paints have enjoyed a renaissance with the consumer due to increased publicity in interior design and home magazines. Their textured, matt finish and distinctive pastel colours provide an interesting alternative to modern paints, and they are particularly in keeping with the character of old and traditional buildings.
In addition to their typical appearance, lime based paints have other unique properties that make them suitable for various remedial solutions. In particular, their high porosity and permeability enables walls to breathe, reducing the risk of dampness.
Externally, lime washes were the most common choice for the walls of buildings particularly in rural areas and small towns prior to the development of modern paint systems. Lead paints were mostly used on joinery and metalwork but are also found on exterior walls of the 18th and 19th centuries. Currently the use of lead based paint is restricted to 0.5 % because lead cause plumbism, (Charles R. Martens, 1968).
Internally, lime washes and distempers were used to decorate the walls of most ordinary houses and all but the principal spaces of the most important houses. Even fine wall paintings and decorative schemes found in 17th century interiors such as the Merchant’s House in Marlborough were commonly executed in lime-based paints.
In the middle of the 20th century, when family farms with dairy barns were common in the Upper Midwest of the USA, white chalk was a necessary part of routine barn maintenance. It was used to lighten the barns and give anti- microbial properties that provide hygienic and sanitary benefits for animals (www.wikipedia). Historically pig’s blood was added to give the colour Suffolk pink, a colour still widely used on house exteriors in some areas of the UK.
White chalk paint powder is a product made up mainly using lime, limestone is a carbonate of either Ca or Mg which are alkaline in nature hence the expected pH value should be greater than 7. Also amount of Ca is expected to be higher than that of CO3 because limestone is calcined and decompose to CaO, for Fe it will only occur in fewer amounts because it is only found as traces (impurities). In addition, density of limestone should be higher than that of chalk and white chalk paint powder because limestone particles are compactly packed to form a dense and heavy rock.
The general objective of this research project is to analyze the chemical content of white chalk powder. The research will also compare the results with contents in limestone and the chalk which forms the basic raw materials.
1.5.1 Specific objectives
The specific objectives were determination of the following compounds:-
- Determination of the pH and density of white wash
- Determination of amount of calcium and magnesium.
- Determination of traces of iron
- Determination of amount of carbonate.
White chalk paint even though a cheaper and easy to make paint, it is not commonly used in painting work especially to the interior walls. The reason for this is because it rubs off and not durable. On the other hand as much as we wish to use an alternative kind of paint (synthetic organic and inorganic pigment), it is turning out to be expensive to paint our houses, and we succumb to paint price fluctuations as a result of rising price of petroleum that forms the basic raw material. Thus there is a need to analyze and quantify the chemical composition of the white chalk. From these analysis we will be able to design a composition with improved characteristics such as; improved adherence, durability etc.
2.1 White chalk paint
White chalk is a paint sold in powder form. It Consists of chalk and lime powder, when mixed with animal glue, water and other additives it forms a white wash which is applied on surfaces for decorative and protective purposes. Addition of pigments and binder is done to increase intensity and impart adhesion on surfaces been applied. It can be used on all types of walls including earth walls, but its lack of water resistance and its poor weathering properties make it inferior to emulsion paint for out door surfaces. However, an addition of tallow or cement gives some degree of durability for external use but easily rubbed or washed off and therefore only suitable for whitening ceilings. Whitewash work effectively on material like bricks made of sand, clay and water due to the quality of absorbing.
Chemical formula: CaCO3
Physical properties :
Appearance : Creamish White powder
Coarse particle on 300 mesh : Max 0.5 %
Sp. gravity : 2.7 to 2.9
PH of 10% aqueous solution : 8.0-9.0
Oil absorption value : 15 to 20
Chemical composition :
CaCO3 : 87.56 %
CaO : 49.38 %
SiO2 : 4.04 %
Paints industries: used in undercoats, primers, distemper, glass putty, cement primer, etc. It is the main ingredients in dry distemper and extender.
Rubber industries: It is commonly used filler in cable wire, foot ware and many rubber products
Plastic industries; used in pesticide formulation
Other uses; used in construction chemicals, foundry, welding rod and many other industries
2.3 Raw materials
White chalk is mainly made of three main components, namely:
- Limestone (CaCO3)
- Whiting (Chalk)
2.3.1. Limestone (CaCO3)
Limestone (mineral) is a common sedimentary rock composed primarily of the mineral calcite (CaCO3). Limestone constitutes approximately 10 percent of the sedimentary rocks exposed on the earth’s surface. The principal component of limestone is the mineral calcite, but limestone frequently also contains the minerals dolomite (CaMg (CO3)2) and aragonite (CaCO3). Pure calcite, dolomite, and aragonite are clear or white. However, with impurities, they can take on a variety of colors. Consequently, limestone is commonly light colored; usually it is tan or grey. However, limestone has been found in almost every color. The color of limestone is due to impurities such as sand, clay, iron oxides and hydroxides, and organic materials.
Calcium carbonate is found in large percentage in these limestone rocks. It is a common substance found as rock in all parts of the world, and is the main component of shells of marine organisms, snails, and eggshells. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid, but high consumption can be hazardous, (Brandy, 1959).
220.127.116.11 Geographical occurrence
Limestone is widely distributed throughout the world in deposits of varying sizes and degrees of purity. It is present in the majority of geological formation. Significant deposit in Kenya are chiefly confined at Sultan Hamud mostly used by E.A Portland Co.ltd, Ortum area in West Pokot, Koru and Homa hills mined by Homa Line co. Ltd. In U.K limestone is found Devonian, Lower Carboniferous, Jurassic, and cretaceous systems. While in U.S limestone deposits are widespread, occurring in nearly every state, usually in tremendous amounts. It is estimated that 15-20% of the area of U.S is underlain by limestone. It should be noted that even though the deposit is extensive, they are frequently so overburdened that quarrying or mining is not economical. Only a small proportion of total limestone is of a suitable grade to meet the high requirements demanded for either industrial lime or limestone for metallurgical and chemical processes. The lower grade stone are generally suitable for agriculture and building uses where the chemical composition is not a limiting factor.
In addition, limestone assumes a bewildering number of widely divergent physical forms with varying purity, with the main chemical being CaCO3 .
These forms include:
- Aragonite a mineral of crystalline calcium carbonate, dimorphic with calcite
- Calcite it is purely calcium carbonate
- Vaterite or (μ-CaCO3)
- Chalk is a soft, fine- grained, fossiliferous form of calcium carbonate that varies widely in color, hardness and purity. Its grain size is so minute that it appears amorphous, but actually it is cryptocrystalline with a very high surface area. it is important to note that Blackboard chalk is calcium sulfate, CaSO4
- Marble is a metamorphic, highly crystalline rock that may be highly calcium or dolomitic limestone of varying purity. It occurs in virtually every color in diverse mottled effects and is the most beautiful form of limestone. It is usually very hard and can be cut and polished to a smooth surface.
- Dolomite: contains over 20% MgCO3 but not more than 46.5 % MgCO3
- Travertine is a calcium carbonate formed from chemical precipitation from natural hot- water mineral springs. In appearance and use it is closely akin to marble.
- Stala and stalagmites are conical, ice like shapes of pure calcium carbonate that forms on roofs and floors, respectively, of caverns. They are precipitated from cold ground water that drips from limestone crevices.
All these materials are essentially carbonate rocks of the same approximate chemical composition as conventionally limestone
Origin of limestone:
Limestone as a constituent of the earths crust is a rock of sedimentary origin from material precipitated by chemical and organic action on drainage waters. Calcium is a common element, estimated to comprise 3-4 % of the earths crust, and the calcium constituent of limestone must have come originally from igneous rocks. The rocks disintegrated by mineral acid action and calcium dissolved and removed in the drainage water into the sea. Some calcium carbonate in the sea may be reprecipitated due to its lower solubility in sea water as a result of changes in temperatures. This process formed purely chemical limestone.
Organic origin limestone is formed through skeleton- building process of marine life. The skeletal structures are almost pure calcium carbonate and are frequently found intact in such limestone as chalk and marl. The calcareous sediment produced in either manner may become contaminated during deposition with argillaceous, siliceous, or ferruginous silt, which affect the chemical composition and nature of the resulting limestone.
The origin of magnesium and dolomitic limestone is uncertain; it is generally believed and considerable evidence support the theory, that it is formed by direct chemical replacement of calcium in limestone by magnesium from waters high in magnesium salts. Several small deposit of dolomite appears to have originated through the co-precipitation of both the carbonates.
The geological origins of calcium carbonates are explained below.
- Geological movements combined with the drying of oceans leaves chalk deposits. Clays and soil components are deposited with time, some may permeate into chalk.
- Minor compaction by late sediments becoming harder with formation of flints. Some compaction occurs to give harder limestone.
- Volcanic activity leads to melting and recrystallisation as marble, (Kirk Othmer, 1979)
18.104.22.168. Physical Properties.
Data are given for materials in their standard state.
(At 25 °C, 100 kPa)
Table 2.1. Properties of limestone
|Molar mass||100.087 g/mol|
|Density||2.71 g/cm³ (calcite); 2.83 g/cm³ (aragonite)|
|Melting point||825 °C Decomposes|
|Solubility in water||.00015 mol/L (25°C)|
|Main hazards||Not hazardous.|
22.214.171.124. Chemical properties
Calcium carbonate shares the typical properties of other carbonates. Notably:
This reaction is important in the erosion of carbonate rocks, forming caverns, and leads to hard water in many regions.
2.3.2. Whiting materials
The mainly used whiting materials are mainly termed as chalk. This is because of their white, colour and mainly used as the pigment in the paint formulation. The chalking material is used in form of micron size particle that can be suspended in liquid media and applied as a coating to various types of surfaces. Among the commonly used whiting materials include; titanium oxide (anatase, rutile), zinc (oxide, sulphide), lead (carbonate and sulphate), calcium and magnesium carbonate. Calcium and magnesium carbonate are the major pigments used in commercial white chalk powder paint.
These pigments are usually fine textured, and vary in colour depending on the deposit. They are found in form of limestone, composed of the remains of small marine organisms such as foraminifera and coccolithophores; it formed after the shells and skeletons of these organisms were deposited in a thick layer on the sea bottom. Chemically, chalk is almost pure calcium carbonate with traces of other minerals. It ranges in hardness and texture from very soft porous varieties to harder close-grained types. Chalk is used together with slaked lime to make whitewash paints. It is also formed from precipitated calcium carbonate (PCC). The PCC has a very fine and controlled particle size, on the order of 2 micrometers in diameter. In some cases, this natural processes yields pure marble of exceptional whiteness, such as the famous deposits at Carrara Italy, (Charles R. Martens, 1968).
An additive is a substance that is added to another material to change or improve its characteristics. In the case of paint, additives are commonly added in paint to improve how the paint flows, to make it stick better and to limit mildew growth. Example of additives used in white chalk paint include: water glass, glue, Portland cement, salt, flour, soil e.t.c.
Liquid glue is used to improve paint toughness and cracking, wheat flour is used as a strength enhancing binder. When flour is used salt is very necessary to prevent growth of mould.
2.4 Industrial manufacturing of white chalk powder
Quarrying limestone and chalk
Approximately 95 percent of the limestone produced in the United States is quarried. After a sufficient reserve (twenty-five years’ worth is recommended) has been prospected, the land that covers the deposit is removed with heavy duty rippers and scrapers (in the case of chalk). If the deposit limestone is close to the surface, an open shelf quarry method can be used; however, this is very rare. Usually an open pit quarry method is used instead. In this method, holes are drilled into the rock, explosives are placed inside, and the rock is blown apart. Depending on the nature of the deposit, a pit can be enlarged laterally or vertically.
Pulverizing the limestone
Once comparatively large chunks of limestone have been quarried, they need to be transported to crushing machines, where they are pulverized to meet the demands of the chalk industry. The first step is primary crushing. Various crushers exist, but the principle is the same: all compress the stone with jaws or a cone, or shatter it through impact. Secondary crushing is accomplished by smaller crushers that work at higher speeds, producing pebbles which are then ground and pulverized.
The next phase, wet grinding, washes away impurities. It is used to make the fine grade of limestone necessary to make white chalk powder suitable for painting purposes. Wet grinding is carried out in ball mills rotating steel drums with steel balls inside that pulverize the limestone until it is very fine.
Calcination of the pulverized limestone
Calcination of limestone using charcoal fires to produce quicklime has been practiced since antiquity by cultures all over the world. The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO2 pressure is only a tiny fraction of the partial CO2 pressure in air, which is about 0.035 kPa.
At temperatures above 550 °C the equilibrium CO2 pressure begins to exceed the CO2 pressure in air. So above 550 °C, calcium carbonate begins to outgas CO2 into air. But in a charcoal fired kiln, the concentration of CO2 will be much higher than it is in air. Indeed if all the oxygen in the kiln is consumed in the fire, then the partial pressure of CO2 in the kiln can be as high as 20 kPa.
The equilibrium pressure is not achieved until the temperature is nearly 800 °C. For the out gassing of CO2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO2. And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898 °C. The decomposition reaction is as follows:
Example of kiln used for calcination. Rotary kiln, Vertical kiln
- After grinding, the particles are sifted over vibrating screens to separate the finer particles
- Pigments (dry, natural, colored materials) are mixed in with the calcium oxide while both are dry, this is done in order to get the desired effect in the hallways of the apartment buildings (the procedure is similar to sifting flour and baking powder together before adding liquid, as in a cake recipe). Addition of colored pigment is optional because when slaked lime undergoes carbonation, it forms the white pigment calcium carbonate, (Kirk Othmer, 1979)
The product from this process is the white chalk powder that is effectively used as a low cost paint. It offers perfect white colors when applied in the interior or exteriors of buildings and other structures. The powder is sold in such brand names as Diamond Cem’, whitewash powder, white chalk powder, lime wash powder, unslaked powder. The powder is packed and sold in 1Kg, 5Kg, 10Kg, & 25Kg in HDPE Laminate attractive bags.
2.5 Preparation of white wash paint
White wash can be made in the following way:
- 8 litres (9 kg) of commercial white chalk powder is mixed with about 18 litres of water. The water is added slowly and stirred constantly until a thin paste results.
- 2 litres of salt is added and stirred thoroughly.
- More water is added to bring the white wash to a suitable consistency.
Additional binders are frequently added to whitewash to provide greater adhesion and binding of the paint film, more flexibility, and variations in porosity. If external quality is required add handful cement per 10 litres white wash just before use.
2.5.1 Surface Preparation and Painting
The preparation of a surface is 90 percent of painting job. Even the highest quality paint won’t adhere properly if the underlying surface is not prepared properly. Good surface preparation means clean and smooth surface. Allow newly plastered surface to mature for a period of at least 6 months before painting.
2.5.2 Application of white wash
- White wash should be done on ceiling prior to walls.
- White wash should be applied with painting brushes. It should be applied vertically and horizontally with the brushes.
- Each coat should be allowed to dry before next coat is applied.
- The brush marks should not be visible after final coat.
- Very economical, cheap and easy to prepare.
- Quick drying, approximately 3hrs of drying.
- Washes off over time if exposed to rain.
3.2. Choice of methods
Complexometric titration method was used in the determination of the amount of calcium and magnesium ions in commercial white chalk paint, limestone and ordinary chalk used in this study. The method is cheap and easily accessible. The process is less time consuming as it does not require complex procedures such as solvent extractions and derivatization techniques. Iron is only present as impurity and only in fewer amounts; therefore for precise determination of the iron elements, atomic absorption spectroscopy (AAS) method was chosen. This method was used because of its high sensitivity; it’s not cumbersome; saves time and almost errors arising from interference are minimized by use of digesting mixture. AAS is based on the principle that matter absorbs light at the same wavelength at which it emits light
3.3. Sample collection and preparation
Three samples were dealt with of which each was collected from different location; the limestone used in analysis was collected from E.A Portland cement ltd in Athi River which had been mined from Sultan Hamud Quarry. The factory uses it in cement production. White chalk paint powder and the chalk were bought from a commercial hardware shop in Eldoret town.
To ensure good and reliable results the samples were finely ground, dried and passed through a 2mm sieve. This was done to increase surface area for chemical reaction and made it easy for dissolution of the samples. The chalk sample was crushed using a pestle and mortar
Limestone which is a hard material was crushed by folding it with aluminum foil and hitting it with a hammer on a hard surface to get fine particles. Whitewash sample was in powder form and needed no crushing. The crushed samples were dried in the air and then passed through a 2mm sieve to obtain the finest particles.
3.4 Preparation of standards and reagents
(i). 250 ml 1M HCl solution
Determining the concentration of acid supplied.
a) Dilution to get required volume and molarity
a few militres of distilled water was put in a 250ml volumetric flask, then the 22.07 ml of the concentrated HCl was gently added into the flask and the volume made up to the mark by addition of distilled water.
(ii).100ml 1M sodium hydroxide solution
Determination of mass of NaOH needed.
1M = 40 g of NaOH in a liter (1000cm3)
4 g of NaOH was weighed accurately and transferred into 100 ml volumetric flask. A few milliliters of distilled water were added and the solid allowed to dissolve completely, then more water was added up to the mark. The flask was then corked.
250ml 0.05m ethylenediaminetetraacetic (EDTA) solutions
Molecular weight of EDTA = 372.24 g = 1 mole
0.05 moles = 18.61 g
Mass required to make 250 ml = 250/100 x 18.61g
4.65g of EDTA was measured and put in a 250 standard flask, then distilled water was added swirling the flask to dissolve the solid. More water was added up to the mark.
Preparation of buffer pH 10 solution
17.5 g of ammonium chloride was weighed and dissolved in 142 ml of ammonium solution in a 250 ml standard flask. Distilled water was added up to the mark. The solution was then corked ready for use.
3.5. Determination of pH using pH metre
The pH value of an aqueous solution is given by the negative logarithm of the activity of the hydrogen ion. The value can be determined by using indicators or various electrodes. In the case of indicators their color changes according to the pH, but those values are not very accurate. The pH meter is very accurate. It consists of two electrodes or a combined electrode. The glass electrode is very sensitive to pH change and the potential difference between the electrodes is proportional to the pH of the solution being measured. The values of pH can be read on the digital readout, (Whitten, 2004).
-250 ml conical flask
-finely ground samples
20 g of every sample was weighed accurately into the conical flask. Then 50 ml of distilled water was added to each flask and swirled on the mechanical shaker for about 30 minutes. The shaker was stopped and the solution allowed to settle, then the samples were then put in the shaker for 2 minutes. The sample was then taken for pH test.
The glass electrode was washed with distilled water and wiped before inserting it in to each of the solution; the PH values were read from the scale.
3.5.1 Density determination.
Density is mass over a unit volume of a compound. Determination involves the measuring of the volume of a known mass of a compound. For powdery sample that is soluble in water the particles are dispersed (particles are separated) in water and all the air expelled from suspension. In a known volume of the suspensions the volume occupied by the particles is then found.
In the case of solid compounds with packed particles e.g. limestone, the volume was determined by measuring the volume of water displaced by the sample, (Rowell, 1994)
Density of whitewash powder.
A 250 cm3 beaker was weighed, 5.02 g of the sample powder was added into the beaker and reweighed. Then 50ml of water was added and then left to boil gently for about 30min to disperse the particles and expel the air. The suspension was then cooled by standing the beaker in running water. After cooling, the suspension plus the washings was transferred into a weighed 250 cm3 volumetric flask. The volume was made to the mark by adding water and then weighed. Chalk was ground first and its density determined just like that of the paint powder.
All the weights were recorded for calculations thereafter.
Density of limestone
Limestone is a hard solid insoluble sample and thus its volume was best determined by volume of water displaced method
The mass of the sample was measured and recorded. A measuring cylinder was half filled (50ml mark) with water and then the sample was gently dipped and allowed to stand at the bottom of the cylinder. The new volume was noted and recorded.
3.5.2 Determination of calcium carbonate
Calcium carbonate being insoluble has to be determined by ‘back titration’ in which it is treated with definite amount of acid and then the excess acid is determined by titration with standard base. In this case HCl and NaOH were used.
The method determines calcium and magnesium carbonate together, but is often expressed as an equivalent amount of calcium carbonate (CaCO3) i.e. the amount of pure CaCO3 that would have reacted with the acid used in the analysis.
Samples (white chalk powder, limestone, chalk)
-250ml conical flask
-100ml volumetric flask
-1 M NaOH
0.75 g of whitewash powder was weighed and put into a beaker and treated with 40 ml HCl acid. When the effervescence was complete the reaction mixture and the washing were transferred into a 100ml standard flask. It was diluted to the calibration mark with distilled water and allowed to mix well by repeated inversion of the corked flask.
Using a pipette, an aliquot of 10 ml was taken into the conical flask and few drops of the indicator. The aliquot was then titrated with 1 M NaOH solution in the burette, this was done gently until the end point was reached. Three consistent titres were obtained, recording the volume of NaOH used in each case.
The whole procedure was repeated for the rest of the sample.
3.5.3 Determination of cations present in the samples
The cations to be determined were Ca, Mg, and Fe and of which Ca and Mg were determined using titrimetric titration Fe was determined using AAS method.
Sample digestion was carried out in order to remove organic materials that acts like interferences during titration and AAS analysis.
-50ml volumetric flask
– Samples to be tested
Preparation of digesting mixture
-lithium sulphate, Li2SO4.H2O
-hydrogen peroxide, 30 %, H2O2 (or 100 volumes)
-sulphuric acid H2SO4, concentrated
0.42 g of selenium powder and 14 g lithium sulphate were added to 350 ml 30 % hydrogen peroxide and mixed well. Then 420 ml concentrated H2SO4 was added slowly and carefully while cooling in an ice bath.
0.3 g of each finely crushed sample was weighed and each put in a dry and clean digesting tube. 4.4 ml digesting mixture was added to each tube the samples were put in a digester together with a blank sample (digesting mixture without samples under test). The preparations were digested at 360oC for three hours until the solutions turned colourless. Then the contents were allowed to cool. About 25 ml of distilled water was added and mixed well until no more sediment dissolved, and then the solution was made up to 50 ml with water and mixed well. The content was stored in storing bottles and allowed to settle so that a clear solution could be taken for analysis.
126.96.36.199 Determination of Ca2+ and Mg2+
Calcium and magnesium are principal soluble cations in the sample. If sodium ions are present they precipitate Ca2+ and Mg2+ in this experiment Na+ ions are provided by ethylenediaminetetraacetate (EDTA) which is a dehydrated disodium salt (Na2.H2Y.H2O). EDTA, in the form of its anion (Y4-) can combine with many cations forming six or four coordinate complexes. The presence of precipitated calcium and magnesium is indicated by a change of color form red to sky- blue (or occasionally, neutral grey) and are expressed in solochrome indicator pH 10 buffer.
Procedure1. Investigation of presence of Ca2+ and Mg2+ ions
5ml of the digested stock was measured into a conical flask and diluted with 5ml of distilled water. The aliquot was then treated with 2cm3 of PH 10 buffer and sufficient solochrome indicator to develop a good color (red).
0.05 M solution of EDTA was put in the burette and titrated against the sample in the conical flask. It was titrated until the indicator showed no trace of red but blue. The titration is repeated for three aliquot samples and volume of EDTA used recorded each at a time.
Procedure 2: Investigation of presence of Ca2+ ions
An aliquot of 5ml was pipetted from the digested stock into the conical flask and diluted with 5ml of water. The aliquot was brought to pH 12 by treating it with 5ml of buffer 10 solution and 5ml of 1M NaOH solution. Sufficient solochrome indicator was added and the sample titrated with 0.05 M EDTA until the indicator changes form pink to blue. The volume of EDTA was recorded. This was repeated for three samples.
188.8.131.52 Determination of Fe using (AAS).
It is the principle method of determining the above element. It is based on the principle that elements absorb light at the same wavelength at which it emits, (Morsden, 1991). When the sample solution is introduced into a gas stream entering the burner, the ions are reduced to neutral atoms. These atoms absorb radiation produced from the hollow cathode lamps. The absorbance is read from the read-out. From the Beer Lambert law, for a given wavelength, the absorption is proportional to the number of absorbance.
Io is the energy emitted.
I = energy entering the detector.
Therefore by plotting absorbance against a series of samples of known concentration, a calibration curve can be produced. This curve can be used to determine atomic concentration in a sample with known absorbance response.
A stock solution of 1000ppm was made from pure compounds. The standards and working solutions were prepared from the stock solution. These working solution were sprayed into the AAS and their absorbance determined. The results were used to construct s calibration curve. The blank and sample solutions were also sprayed into AAS and their absorbance determined. Their concentrations of the sample were determined using the curve.
4.1. RESULTS AND DATA ANALYSIS
4.2.1 pH values
The pH values of various samples are shown in the table.
Table 4.1 pH values
White Chalk Powder
Mass of beaker 83.75 g
Mass of beaker + sample 88.77 g
Mass of the sample 5.02 g
Mass of flask 162.24 g
Mass of flask + suspension 392.03 g
Mass of suspension 229.79 g
Blackboard Chalk Density
Mass of beaker 83.75 g
Mass of beaker + sample 88.75 g
Mass of the sample 5.0 g
Mass of flask 162.24 g
Mass of flask + suspension 418.95 g
Mass of suspension 256.71 g
Density of Limestone
Mass of sample 9.7 g
Initial volume 50 cm3
Final volume 53 cm3
4.2.3. Calcium carbonate
Results for back titration of the samples with NaOH are as shown in the tables
Table 4.2(a) titration with White chalk paint powder.
|Final burette reading||03.70||07.20||10.80|
|Initial burette reading||00.00||03.70||07.20|
|Volume of NaOH used (cm3)||03.70||03.50||03.60|
Table 4.2 (b) titration with limestone sample
|Final burette reading||02.20||05.20||08.20|
|Initial burette reading||00.00||02.20||05.20|
|Volume of NaOH used (cm3)||02.20||03.00||03.00|
Table 4.2 (c) titration with chalk sample
|Final burette reading||1.2||03.50||06.80|
|Initial burette reading||00.00||01.20||03.50|
|Volume of NaOH used (cm3)||02.70||02.80||02.70|
4.2.4 Calcium and magnesium
Tables shows the results of volume of EDTA used in titration for determining occurrence of both Ca2+ and Mg2+ ions in the samples.
Table 4.3 (a) result with white wash powder
|Final burette reading||13.00||25.00||37.50|
|Initial burette reading||00.00||13.00||25.00|
|Volume of EDTA used (cm3)||13.00||12.00||12.50|
Table 4.3(b). Result with limestone
|Final burette reading||03.60||07.10||14.30|
|Initial burette reading||00.00||03.60||10.70|
|Volume of EDTA used (cm3)||03.60||03.50||03.60|
Table 4.3(c). Results with chalk
|Final burette reading||24.70||24.30||24.50|
|Initial burette reading||00.00||00.00||00.00|
|Volume of EDTA used (cm3)||24.70||24.30||24.50|
The tables show results of the values of EDTA obtained in determining presence of Ca2+ ions.
Table 4.4 (a). Results with white wash powder
|Final burette reading||03.00||6.00||09.00|
|Initial burette reading||00.00||03.00||06.00|
|Volume of EDTA used (cm3)||03.00||03.00||03.00|
Table 4.4 (b). Result with limestone
|Final burette reading||03.20||06.40||09.60|
|Initial burette reading||00.00||03.20||06.40|
|Volume of EDTA used (cm3)||03.20||03.20||03.20|
Table 4.4 (c). Results with chalk
|Final burette reading||14.7||29.00||14.50|
|Initial burette reading||00.00||14.70||00.00|
|Volume of EDTA used (cm3)||14.70||14.30||14.50|
Table 4.5 shows Results of iron values from AAS analysis.
|White chalk powder||1.397|
4.3 Data analysis
- Densities of the Samples.
Density of white chalk paint powder
From the results obtained, mass of water in the flask can be found as;
Mass of suspension – mass of dry sample
=229.79 g – 5.02 g
Since the density of water is 1 gcm-3
Then the volume of water in the flask = mass/density
Density of chalk
Determination of chalk density is also calculated using the above method. it was found to be 2.92g cm-3
Density of limestone
Density of limestone = mass/ volume
From table 4.2 (a)
- CaCO3 in whitewash
Equal amount (mol) of HCl that reacted with NaOH in equation (4.2) therefore the number of moles of HCl = 3.6 x 10-3 moles in 10 ml aliquot.
= 0.04 moles
Hence the HCl which reacted with the carbonate
= 0.04 moles – 0.036 moles
= 0.004 moles
From equation (4.1) 2 moles of HCl reacts with 1 mole of CaCO3.
|White chalk powder||chalk||limestone|
Determination of amount of calcium and magnesium
i.e. 3.125 x 10-3 mol Ca2+ + Mg2+ in 0.3 g of the sample
Determination of Ca2+
Volume of EDTA used is 1.5 ml and so the number of mol of EDTA used in the titration is
0.05 mol l-1 x 1.5/1000L = 0.000075 mol
The amount of Ca2+ is therefore also 7.5 x 10-5 mol. This is in 5ml of the solution, and so in 50 ml there is 7.5 x 10-5 mol x 50/5 = 7.5 x 10-4 mol. This comes from 0.3 g of the sample powder.
i.e.7.5 x 10-4 mol of calcium is in 0.3g of the sample
Mass of calcium = R.A.M x number of moles
= 40 x 7.5 x 10-4 mol
= 3.0 x 10-2 g calcium per 0.3 g
=30 mg of the sample is calcium
= 30mg/0.3g x 1g
Determination of Mg2+
Amount of Mg = amount of Ca and Mg – amount of Ca
=3.125 x 10-3 mol – 7.5 x 10-4 mol
= 2.375 x 10 -3 mol Mg2+
Mass of Mg = R.M.M x no. of moles
= 24 g x 2.375 x 10 -3 mol
= 5.7 x 10 -2 g of sample (0.3g) was Mg
i.e. 57 mg in 0.3g
Therefore in 1 g of the sample we have; 57mg / 0.3g
= 190 mg/g.
Comparing to the total amount of Ca and Mg present in the Sample, 24 % of it is Calcium and 76% is Magnesium.
The same method was used to analyze Ca and Mg amount in limestone and chalk. The values obtained are as shown in the table.
Table 4.7. Amount of calcium and magnesium
|White chalk powder||100 mg/g||190 mg/g.|
Density is ratio of the mass of a body to its volume, usually expressed in grams per cubic metre. The relative density of the substance is numerically equal to its density expressed in grams per cubic centimeter. From the data analysis limestone had the highest density (3.23gcm-3) which is slightly above the postulated 2.71 g/cm³ (calcite); 2.83 g/cm³ (aragonite) this could be due to different types of limestone and methods of formation. Chalk and paint powder had low density values 2.92 g/cm³ and 0.2 g/cm³ respectively, basically because their particles are sparsely packed and hence few grams of the particles are dispersed in a large volume.
The major objective of this study was to determine chemical composition and properties of white chalk paint powder and compare it with that of some of its major raw materials. pH is defined as the negative logarithm of the concentration of H+ ions (protons): pH = -log10[H+], where [H+] is the concentration of H+ ions in moles per litre. Its value gives the acidity or basicity of the sample under test. The pH of the sample ranges from 8.21 to 8.9; this suggests that the samples are alkaline, probably due to the presence of calcium carbonate which is the main component in the above samples. limestone was found to have the highest amount of calcium carbonate of 71.43 % with white chalk having the least amount, this may be attributed to the raw materials (limestone and chalk) when calcined decompose and the carbonate (CO3) that that take part in reaction. The calcined from of limestone is calcium oxide and acts as a binder when painting since it has cementious property. The amount of CaCO3 in the paint powder is 26.6 % and acts as the pigment. From the hypothesis all CaCO3 present in the white chalk powder must have come from limestone and chalk, therefore to % amount of chalk and limestone in the paint powder can be calculated as shown in table 5.1.
Table 5.1: Determination of % limestone and chalk in white chalk paint powder.
|% Amount 0f limestone||71.43/134.93 x 100
|% Amount of chalk||63.5 / 134.93 x 100
Therefore the amount of limestone in the paint powder is more than that of chalk. CaCO3 has high refractive index and reflects lights giving lighting characteristic when applied on a surface. This is a very important decorative function of paint.
Calcium and magnesium are the main cations in the sample with calcium been more than magnesium per gram of limestone and chalk (see table 5.2).
Other elements like Fe, Si and Al are present as impurities; limestone had the highest amount of impurities.
Table5.2. The table shows a summary of values obtained from the analysis.
|White chalk powder||26.6 %||100||190||2.92||8.9||1.397|
The following are suggested recommendations.
- To minimize the rate of rubbing off of the white wash paint, a formulation should be developed that has a good adhesive material. This should be incorporated during manufacturing process to ensure homogeneity in the mixture. This adhesive should be able to bind the pigment on the surfaces without interfering with decorative and protective properties. For example a small amount of white cement can be added to increase binding strength of the white wash paint. When white cement is to be used, this should be added at point of use because the paint solidifies a very short time.
- In addition to this liquid animal glue should be used together with water to make the paint emulsion. If this is considered, a non-rubbing and durable paint film can be reached. Analysis should be done to determine the best amount of cement and glue that can be used and still ensure decorative, protective and functional properties of white wash paint.
- Further analysis can be done to determine traces of heavy metals such as Pb and Hg which are toxic when assimilated into the body. Animals such as goats lick the walls painted with these lime washes and if these heavy metals are in the paint can be passed through the food chain. Also traces of iron should be minimized to zero as iron when hydrolyzed forms a brown stains (rust) on walls. This can be done by considering use of pure raw materials.
- Also, analysis should be done to determine the amount of silicon and aluminum, which could not be tested due t lack of respective lamps in the AAS. These elements might be present because they form impurities in limestone.
White chalk paint has the following composition: 26.6% Calcium carbonate, Calcium ion 100 mg/g, magnesium ion190 mg/g, iron 1.397 mg/kg, density 2.92 gcm-3 and a pH value of 8.9. From the consideration that all the Calcium carbonate comes from limestone and chalk, then 52. % of the calcium carbonate in the paint was from limestone and 47 % from chalk
Calcium and magnesium carbonates acts as the white pigment, the whiteness is as a result of the diffuse scattering and reflectance of light by a myriad of fine particles and the fact that they do not selectively absorb any of the wavelengths of visible light, hence the pigment produce opacity by virtue of the light they absorb. The CaO formed from calcination process act as the binding material which when slaked and applied it binds by a curing process known as carbonation reaction, to form a luster surface of CaCO3.
Calcium and magnesium carbonate are basic supplemental pigments for practically all types of paint from dry powder paints through emulsion paints to house paints. Their alkalinity inhibits growth of microorganism and hence gives antimicrobial protection on surfaces.
The pigments are economical because of low binder demand since they bind through action of CO2 on the CaO in the paint film. In addition the raw materials are locally available and needs less technical process to manufacture.
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