Determination of Calcium and Magnesium in Limestones and Dolomites

Determination of Calcium and Magnesium in Limestones and Dolomites. Application of the Ethylenediaminetetraacetic Acid Method. JOHN J. BANEWICZ and...
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Determination of Calcium and Magnesium in limestones and Dolomites Application of the Ethylenediaminetetraacetic Acid Method JOHN J. BANEWICZ AND CHARLES T. KENNER Department of Chemistry, Southern Methodist University, Dallas, Tex. CHWBRZENBACH and coworkers (1, 4, 5 ) suggested the

S use of ethylenediaminetetraacetic acid (commonly known as Versene) as a complexing agent for the alkaline earth and other metals and as a titrant for the sum of calcium and magnesium in water using Eriochrome Schwartz T (Indicator F 241) as an indicator. Diehl, Goetz, and Hach ( 2 ) studied this method further, especially as applied to the determination of the total hardness, the calcium hardness, and the magnesium hardness of waters. Because the direct titration of a solution containing calcium and magnesium gives the sum of these two elements, they suggested the use of the oxalate separation of calcium, followed by titration of magnesium in the filtrate to obtain the calcium by difference. The purpose of this investigation was to apply this method to the determination of the calcium oxide and magnesia content of a series of limestones and dolomites. REAGENTS AND SOLUTIONS

Reagents. All reagents used were C.P. or analytical grade chemicals which conformed to AMERICAN CHEUICALSOCIETY specifications. Primary standard grade disodium dihydrogen ethylenediaminetetraacetate (disodium dihydrogen Versenate) was used to prepare the titrating solutions. The indicator used was Potting Black C, Colour Index No. 203, made by the Ciba Co., Inc., and also known as Indicator F 241. Solutions. STANDARD VERSENATE.Approximately 4.00 grams of disodium dihydrogen ethylenediaminetetraacetic acid and 0.1 ram of magnesium chloride hexahydrate were dissolved in sufcient water to make 1 liter of solution. This solution was standardized against a standard calcium solution. STANDARD CALCIUM. Calcium chloride dihydrate was recrystallized twice and then precipitated with ammonium carbonate. The calcium carbonate was washed and ignited a t 400' C. in a muffle for 4 hours. .;i 1-gram sample of the calcium carbonate was weighed accurately by difference, dissolved in a small volume of hydrochloric acid (1 to l ) , and diluted to 1 liter in a volumetric flask. STANDARD MAGNESIUM. .-I large excess of ammonium oxalate monohydrate was added to a saturated solution of magnesium chloride hexahydrate, causing the precipitation of heavy metals and some magnesium oxalate. The precipitate was removed by filtration and the solution was evaporated to cause partial precipitation of the magnesium oxalate. The magnesium oxalate thus obtained was filtered, washed, dried, and ignited a t 500" C. in a muffle to convert it to the oxide. The oxide was weighed by difference in a closed container and made up t o volume in a volumetric flask. The solution was further checked by titration against the Versenate solution standardized against the standard calcium solution. The calculated value agreed with the titration value within less than one part per thousand. KNOWN SOLUTIONS O F CALCIKM A N D hIAGSESIUM. Solutions were prepared by using various volumes of the standard solutions and diluting in a volumetric flask. AMMONIACAL BUFFER. Approximately 67.5 grams of ammonium chloride were dissolved in water, 570 ml. of concentrated ammonium hydroxide were added, and the solution ?vasdiluted to 1 liter. AMMONIACAL BUFFERED OXALATE.Approximately 140 grams of ammonium chloride, 6.0 grams of ammonium oxalate monohydrate, and 14 ml. of concentrated ammonium hydroxide were dissolved in sufficient water to make 1 liter of solution. k E T A T E BUFFERED OXALATE.Approximately 5.0 grams of ammonium oxalate monohydrate and 3.0 ml. of acetic acid (99.5%) were dissolved in water and diluted to 1 liter. INDICATOR SOLUTION.One-half gram of Potting Black C was dissolved in 100 ml. of ethyl alcohol. This solution was unstable and could not be used after a few days. However, Wright (6)has found that the indicator is stable if stored in the absence of air under a blanket of nitrogen.



Solution of Samples. Approximately 1-gram samples were

weighed accurately, dissolved in 10 ml. of hydrochloric acid

(1 to 1) and 25 ml. of water, and evaporated to dryness. The residue was baked for 1 hour, dissolved in 10 ml. of hydrochloric acid (1 to 1) and 25 ml. of water, filtered, and washed. If the amount of residue was appreciable, the paper was ignited and the residue fused with sodium carbonate. The fusion mixture was dissolved in hydrochloric acid (1 to l), filtered, and washed and the filtrate was added to the original filtrate. The combined filtrates were diluted to aproximately 450 ml. in a 500-ml. volumetric flask, the pH was adjusted to 5 to 7 by use of concentrated ammonium hydroxide, and the filtrate was diluted to 500 ml. The iron and aluminum precipitate, if formed, was allowed to settle in the solution. Aliquots of this solution were then used for the determination of calcium and magnesium. If the iron and aluminum precipitate was large, it carried down some calcium and magnesium, causing the results to be low. This error was offset by redissolving the precipitate by dropwise addition of hydrochloric acid before dilution to volume and removal of aliquots. However, the iron and aluminum then precipitated upon addition of the buffered oxalate in the calcium separation, thus slowing down the filtration. I t Tvas found that the optimum procedure for both accuracy and speed in cases of appreciable iron and aluminum and low magnesium was to cause formation of the precipitate by one drop of ammonium hydroxide in the pH adjustment procedure and to pipet the magnesium samples immediately after dilution to volume and settling of the precipitate. The precipitate was then redissolved by addition of a few drops of concentrated hydrochloric acid and the total calcium and magnesium samples were pipetted. Total Calcium and Magnesium. Aliquots of 10.00 ml. were pipetted and diluted to approximately 100 ml., 2 ml. of the buffer and 3 drops of indicator were added, and the solution was titrated to a pure blue end point. KO blank was necessary. In the samples in which the dissolving of the iron and aluminum precipitate was necessary, the solution was titrated using the indicator inhibited with hydroxylamine hydrochloride suggested by Diehl, Goetz, and Haeh (2) (4.5 grams of hydroxylamine hydrochloride in 100 ml. of the usual indicator solution). Even with the use of this inhibited indicator, the iron still caused some interference in the end point. This interference was minimized by withholding addition of the indicator until just before the end point n-as reached. Separation of Calcium. Two methods of precipitation of calcium oxalate were tested. The ammoniacal buffered oxalate precipitation outlined by Diehl, Goetz, and Hach ( 2 ) was tried first. This involved pipetting 25.00-ml. aliquots of the sample solution and adding 20 ml. of the ammoniacal buffered oxalate. The precipitate x a s allowed to stand 4 hours and was then filtered through fine-porosity fritted-glass funnels. The second procedure tested n-as a modification of the acetate-buffered oxalate precipitation described by Holth ( 3 ) . I n this method a 25.00-ml. aliquot of the sample solution was pipetted into 50 ml. of the acetate-buffered oxalate solution, to which 1 gram of solid ammonium oxalate had been added. The solution was then heated on a steam hot plate for 20 to 30 minutes and allowed to stand a t room temperature for 4 hours before being filtered through a fineporosity fritted-glass funnel. It was found that the additional solid ammonium oxalate was necessary to ensure complete precipitation, but that more than this amount caused indistinctness inthe end point. Titration for Magnesium. The filtrate from the calcium separation was diluted t o approximately 200 ml., 15 ml. of buffer solution, 10 ml. of concentrated ammonium hydroxide, and 20 ml. of hydrogen peroxide (3'%) were added, and the solution was allowed to stand 1 hour. Seven drous of indicator were added and the solution was titrated with stanaard Versenate. Three drops more of the indicator were added just before the blue end point was obtained. The usual blank was about 0.06 ml. Analysis of Known Solutions. Solutions containing known concentrations of calcium and magnesium were titrated for total calcium and magnesium and for magnesium after separation of calcium by both methods. Solution I was 0.01184 A4 in magnesium and 0.07959 $1 in calcium, while solution I1 was 0.05918 M in magnesium and 0.04976 M in calcium. Determination of Effect of Strontium. Because some limestones contain small amounts of strontium, a known conoentration of this element was added to the known calcium and magnesium solutions and analyzed in the usual way. The strontium titrates


V O L U M E 2 4 , NO. 7, J U L Y 1 9 5 2


Table I. Analysis of Known Solutions

Solution I I1

Calcd. 2.98 14.90

0.09929 M Versenate Required, M1. For h l g (25.00-Ml. Aliquot) Found For Ca plus M g (10.00-M1. Aliquot) Acetate Ammonia procedure procedure 9.21 9.2010.01 2.98f0.00 3.0910.02 14.84 f O . 0 1 14.92 i : O . O l 1 0 . 9 7 1 0 . 9 6 dcO.02

usual procedures. This was also the reproducibility of the total calcium and magnesium titration. The adjustment of the pH to a value between 5 and 7 causes precipitation of iron and aluminum and thus removes the interference of these elements in the subsequent procedures. However, if the amount of this precipitate is large, it must be redissolved before removal of aliquots for the total calcium and magnesium titration in samples low in magnesium and must not be allowed to form in samplea high in magnesium.

Table 11. Analysis of Bureau of Standards Samples NBS Value


Acetrtte Procedure Limestone, N B S l a CaO, 70 41.32 41.35 f O . 0 4 MgO, 70 2.24a 2 . 1 0 i: 0 . 0 1 D X B S 88 CaO % 30.49 30.54&0.05 Rigd, 21.48 21.43 1 0 . 0 6 Corrected for inclusion of SrO.

Ammonia Procedure 41.25 +0.08 2.17 1 0 . 0 1 3 0 . 4 9 1 0 10 21.45 f O . 1 0

before magnesium in the total titration and small amounts (up to a t least 0.3% of a 1-gram sample) remain unprecipitated with the magnesium in the oxalate separations. Thus the magnesium will be high by an amount equivalent to the strontium present.


As shown in Tables I and 11, the results by either method of separation are satisfactory for both calcium and magnesium. This method was used in the analysis of 500 samples from a continuous core of an oil well with satisfactory results. The chemical analyses satisfactorily explained all apparent anomalies in the porosity and permeability measurements by showing the presence of free calcite incorporated with dolomite. The presence of crystals of calcite in the dolomites with apparently anomalous porosity and permeability measurements was further substantiated by photomicrographs of thin sections of the samples. LITERATURE CITED

( 1 ) Biedermann, TV., and Schwarzenbach, G., Chimia, 2, 56 (1948). DISCUSSION

The end point in the titration for magnesium after separation of the calcium oxalate was affected by the excess oxalate present and was very indistinct and unsatisfactory. The addition of hydrogen peroxide before titration was found to give a satisfactory and reproducible end point, even though there is apparently no reaction between the hydrogen peroxide and the be reproduced to 0'02 ml' Oxalate. Such end points in separate aliquots of the same solution carried through the


(2) Diehl. H.. Goetr. C. A.. and Hach. C. H.. J . Am. Water Works Assoc., 42, 40 (1950). (3) Holth, T., A ~ cHEM., ~ 21, ~ 1221 , (1949). (4) Schwarrenbach, G., and Ackermann, H., Helv. Chim. Acta, 30, 1799 (1947). )'( 31y lo2' (1948)* (6) Wright, E.R., Dow Chemical Co., Freeport, Tex., personal com-

munication. RECEIVEDfor review January 28, 1951. Accepted April 8, 1952. PreCHEMIsented st the Seventh Southwest Regional Meeting of the AMERICAN CAL SOCIETY, Austin, Tex., December 1951.

Identification of Salts of Di- and Triaminoguanidine by Powder X-Ray Diffraction Methods JOHN P. OLATTA AND JOHN J. PITHA' Department of Chemiotry, Michigan State College, East Lansing, Mich.

HE x-ray diffraction patterns of some salts of di- and triTaminoguanidine have proved t,o be useful in identification of the salts than is the criterion of melting point. The use of melting point as a criterion for purity and for identification of salts of di- and triaminoguanidine was unsuitable because of the behavior of these salts upon heating. In the process of determining the melting point of any of these salts, even after several recrystallizations, several anomalies are observed. The solid shrinks in volume, and then curling and writ.hing of the solid are observed. Melting finally occurs over a fairly wide temperature range, usually accompanied by decomposition. The technique of powder x-ray diffraction offered a rather rapid and conclusive method for the identification of these salts, although such patterns do not reflect the purity of the sample to any degree. In this work it was found very helpful to have a t hand films and tables w1t)h diffraction patterns and d Salt" values that could be readily referred to for rapid DAG,HI comparison and identification. DAG. HBr PREPARATION O F MATERIALS

In general, the salt,s studied were prepared by either the hydrazinolysis of s-methyl-3-thiosemicarbazide hydroiodide followed by conversion by double decomposition reactions to the desired diaminoguanidine salt, or by the hydrazinolysis of the 1 Present address, Transformer and Allied Products Laboratory, General Electric Co., Pittsfield, Mass.

corresponding salts of aminoguanidine, giving rise to the desired salt of triaminoguanidine. Details of these syntheses are found in the literature (1-3). All materials studied were recrystallized several t.imes from water and, after separation by filtration, were dried in vacuo over porous barium oxide. Hydrazine content waa determined by the method of Keim, Henry, and Smith (1) and analytical procedures. The anion content by prepared, along with analysis and melting range, are listed in Table 1. X-RAY DIFFRACTION PA'ITERNS

The x-ray diffraction patterns were made using a standard North American co. diffraction unit by means of the Stramani films technique, The cameras had a diameter of 114.59 mm. and allowed rotation of the sample. The samples

Table I. Compounds Investigated

Melting point, C. Lit. Obsd. 134-136 ( 8 ) 131-133 262-263 ( 8 ) 158-160 158-160 (e) D A G . HNOa 143-144 138-140 (D.4G)z. HzSOa 234 ( 3 ) 209-211 D A G . HxSOa ... 146-148 ... 174-177 232 223d T A ~H, B r 232 223d TAG. H N O Z 216 215d ( T . ~ G ) ~ ( H Z S O ~ Z . ~ H Z. O. 150-165b DAG denotes diaminoguanidine. TAG denotes triaminoguanidine. b Decomposition.



Composition, % NzHa Anion ... 3227 ... 47.0

... ... . .. 68:60

52.0 57.36 52.97

Analysis, % KzHa Anion

... ... .. .. . .,.

55.25 34.79 51.30 63.46 25.23 43.29

68:60 52.25







34:a5 50.60 63.32 24.99 43.29 36'32