CA1063103A - Mixed alkali metal-magnesium salt of crosslinked starch xanthate and process of preparation - Google Patents

Abstract

MIXED ALKALI METAL-MAGNESIUM SALT OF CROSSLINKED
STARCH XANTHATE AND PROCESS OF PREPARATION

ABSTRACT

Mixed alkali metal (sodium or potassium)-magnesium salts of crosslinked starch xanthates are prepared by incorporating a critical amount of a water-soluble magnesium salt (e.g. magnesium sulfate) in the reaction slurry prior to dewatering the xanthated starch. The rate of dewatering by filtration or centrifugation is accelerated, and the resulting product has improved properties for use in removing heavy metal ions from aqueous solutions.

Description

~Q~;3i~3 BACKGRO~IND OF THE INVENTION ~ :

This invention relates to an insoluble crosslinked-starch xantha-te composition useful for removing heavy metal ions from aqueous solutions.

In U.S. Patent 3,947,354 a method was disclosed for removing heavy metal ions from aqueous solutions by precipitating a water-insoluble complex formed from a water-soluble cationic polymer, a water-soluble starch-xanthate, and the heavy metal ions. It is also disclosed in the above-mentioned patent that water-soluble starch-xanthate alone would coprecipitate with the 10 heavy metal ions, but this coprecipitation resulted in a very ~ ~;
inefficient heavy metal ion removal which did not meet present- ;~ ;
day discharge limits.

Other investigations have shown that water-soluble starch xanthates in combination with cationic polymers form polyelectrolyte complexes that effecitvely remove heavy metals rom waste water.
C.L. Swanson, R.E. Wing, W~Mo Doane, and C.R. Russell, Environ. ;
Sci. Technol., 6, 614(1973); and R.E. Wing, C.L. Swanson, W.M.
Doane, and C.R. Russell, Water Pollut. Contr. Fed. J., 46, 2043 (1974). Research has continued with the goal of eliminating the 20 expensive cationic polymer to give a more economical method of heavy metal removal. More recently, it has been disclosed that xanthation of highly crosslinked starch gives a water-insoluble product that is effective in removing heavy metals from water -~
without the need for a cationic polymer. R.E. Wing, W.M. Doane, and C.R. Russell, J. Appl. Polymer Sci., 19 847-854 (1975); and United States Patent 3,979,286, of September 7, 1976.
.~ , .
The last cited publication and patent described the `
conversion of insoluble sodium starch xanthate to the magnesium salt, the conversion being accomplished by repeatedly washillg the 30 product with an aqueous solution of magnesium chloride. Analysis of the converted product indicated that the conversion was 99%

- 2 .

i31C)3 ~fective. It was observed that the magnesium insoluble starch xanthate appeared to have yood room~temperature stability for several months and was very effective in metal removal~

SUMMARY OF THE INVENTION

Mixed alkali metal (sodium or potassium)-magnesium salts of crosslinked starch xanthate are produced by incorporating an amount of the water-soluble magnesium salt in the reaction ~ ;
slurry prior to dewatering the xanthated starch which provides from 0.2 to 1.6 parts by weight of magnesium per each part by weight of xanthate sulfur. The xanthated starch is then 10 dewatered by filtration or centrifugation. The resulting product may contain from 0.5 to 10 moles of alkali metal per mol of magnesium. In the pre~erred process, from 0.26 to 0.8 parts by ;~`~
weight of magnesium are employed per part oE xanthate sulfur, and the resultin~ product is characterized by containin~ from 1 to 2 moles of alkali metal per mole of magnesium. Part of the alkali metal and magnesium are complexed with the starch xanthate to form the mixed sal , and some magnesium and alkali metal are present in the form of other compounds, such as magnesium hydroxide. The advantages of the process and 20 product over the prior art processes and products are described below.

DETAILED ~ESCRIPTION OF T~E INVENTION

Crosslinked-starch-xanthate, that is, insoluble-starch-xanthate (ISX), is defined herein as granule starch which has been crosslinked with the var-ous known crosslinking agents and which is subsequently xanthated. Xanthation is normally conducted in the presence of an alkali metal base such as sodium or potassium hydroxide. In the ensuing discussion, sodium hydroxide will be used for illustration purposes only, with the understanding that potassium hydroxide may be substituted as an equivalent thereto.

- 3 31~3 Crosslinked-starch starting materials, which are useful in accordance with the invention, inc]ude granule sta~ches which have been crosslinked with epichlorohydrin, phosphorous oxychloride, sodium trimetaphosphate, anhydrides of dicarboxylic acids, acrolein, formaldehyde, glyoxal, and N-methylolureas (Encyclopedia of Polymer Science).

The crosslinking occurs between the respective starch molecules themselves. Specifically, the crosslink is between the hydroxyl oxygens. The type and degree of crosslinking must 10 be such that sufficient reactive sites are available for attachment of xanthate groups and that the ISX product is insoluble in water and all other solvents. It is the degree of crosslinking that determines the insolubility of the crosslinked-starch starting material and of the xanthated product.

Insolubility in crosslinked polymers is usually defined in terms of gelation and swelling of the crosslinked granules. At the gel point nonlinear polymers (in this instance crosslinked-starches) change from viscous liquids to elastic gels which are characterized as being nonfusable and insoluble (Paul J. Florey, 20 "Principles of Polymer Chemistry," Cornell University Press, Ithaca, New York, 1953, p. 47). According to Florey, one crosslink between two primary molecules is sufficient to bring on gelation (Florey, supra, p. 358). Crosslinked-starches having one crosslink between two starch molecules would, therefore, be theoretically useful as starting materials in the preparation of ISX's. However, the degree of crosslinking in any polymer system is difficult to measure.

Florey (supra, pp. 581-583) shows that degree of cross-linking can be related to the degree of swelling that a network 30 structure exhibits in a particular solvent system. As degree of crosslinking increases, degree of swelling decreases. Crosslinked-starches useful in accordance with the invention have a degree of crosslinking such that they exhibit a degree of swelling in ;~
.

.. . . .

~ 63~ 3 ater at 95 C. of not over 450~, such as within the range from ;~
65~ to 450~ of the volume of unswollen crosslinked-starch.
Starch crosslinked to a degree of swelling less than 65~ can be used but is not commercially available at the present time. The ISX's exhibit essentially the same degree of swelliny as the crosslinked-starches from which they are prepared. ISX's having degrees of swelling of less than 75~, such as 65-75%, are preferred in that they are sufficiently insoluble to be easily filtered or centrifuged after being used to remove heavy metal ions from 10 solutions. However, the more highly swellable ISX's, which would be difficult to filter, are useful in removing heavy metals from aqueous solutions, as long as they are adequately contacted with the heavy metal ions and recovered by some suitable means, such as centrifugation.

Capacity of the ISX in removing heavy metal ions depends entirely on the number of xanthate groups attached to the composi-tion in comparision to the number of heavy metal ions in solution.
Theoretically, one xanthate group (xan) for every metal ion (M) would remove all metal ions. For the reasons given above for 20 the inahility to accurately determine degree of crosslinking, it is difficult to accurately determine the molecular weight of the ISX. However, assuming a degree of crosslinking of 10 AGU/crosslink (cl), the molecular weight of ISX having a xanthate degree of substitution ~D.S.) of 0.2 would be about 3% greater than the corresponding noncrosslinked-starch-xanthate. Since 10 AGU/cl ;~
constitutes a highly crosslinked-starch, it becomes obvious that an error in the actual degree of crosslinking at any level would be insignificant when calculating the amount of composition necessary to give a 1:1 ratio of xan:M. To obtain a 1:1 molar 30 ratio of xan:M, one mole of heavy metal ion would require 0.91 g.

of a ISX having a xanthate D.S. of 0.2 and a 10 AGU/cl degree of crosslinking. But xanthate D.S. is not critical. Decreasing xanthate D.S. in ISX simply requires more composition to maintain the nscessary xan:~ ratio . The preferred ISX's have D.S.'s of from 0.1 to 1.0 and are effective in heavy metal ion removal.

.
, 3~ 3 -- Adding ]SX to a~ueous solutions increases pH. Since pollution regula-tions usually require the effluent discharged into streams to have pH's of from 6-9, it is preferable that the amount of ISX added to heavy metal containing industrial effluents be such that the final pH is within acceptable limits. This sometimes ;~
requires adding acid or base to the effluent.

Xanthation of starch is a well-known reaction (cf. I'Starch: ;
Chemistry and Technology," ~histler and Paschall, ed., Academic ~`
Press, New York and London, 1965, pp. 455-458) in which starch is 10 contacted with carbon disulfide in a basic medium. Sodium or -~
potassium hydroxide is present in excess over the amount of xanthate groups introduced as the sodium or potassium xanthate salt. In a number of tests, the reaction of crosslinked-starch and varying ;~
amounts of sodium hydroxide and carbon disulfide resulted in crosslinked products having varying xanthate D.S.'s, in the sodium salt form, but all were effective in heavy metal ion removal.
Times of xanthation o~ 1, 4, and 16 hr. resulted in essentially the same products, all other parameters being the same. A 30-min.
xanthation resulted in a slightly lower xanthate D.S. When solids ~;-20 concentration was increased from 10~ to 25~,similar products were obtained. The xanthation reaction is about 70-75% efficient so -excess CS2 must be used. ;

The xanthation reaction with granule starch in an a~ueous alkaline slurry can be represented as follGws:

(NaOH) S
starch-O-Na+CS2 ~ starch-O-C-S Na+

Since a basic medium is used for both c~osslinking and xanthation, an investigation was made of the preparation of ISX
without isolation of the crosslinked intermediate. AftRr the starch had been crosslinked, additional base and then carbon ~
30 disulfide were added. The products obtained were essentially ;
the same as those obtained in a separate two-step reaction and were effective in removing heavy metal ions from solutions. ~ -:.
A study and evaluation of the use of magnesium salts with ~631~3 ::~ISX in preparations and product stability led to the use of .~gnesium sulfate directly in the xanthation mixture, as the ~ ;
most preferred embodiment. The amount of magnesium ion in relation to xanthate sulfur is of critical importance.

A preliminary s-tudy was made under constant reaction conditions ~crosslinked starch, 100 g.; sodium hydroxide, 45 g.;
carbon disulfide, 15 ml.) to determine the optimum amount of magnesium ion required to yive the most rapid dewatering rate.
The time required for dewatering the product was used as the lOdetermining factor.

ISX having a D.S. in the range of 0.1 to 1.0 would have sulfur contents of 3.72% to 24.57~. The preferred ISX would have a D.S. range of 0.1 to 0.35 and a sulfur content of 3.72% to 10.84%.
These values are calculated on the basis that the ISX is water free and in sodium salt form. The same basis applies to the ranges set out below for grams magnesium per 1% sulfur.

Figure 1 shows an effective range of magnesium incorporation ;
to be from about:0.2 to about 1.6 g. magnesium ion for each 1% ;~
sulfur desired in the product, with a preferred range of from 200.26 to 0.8. The optimum amount was determined to be about 0.4 g. -;
magnesium ion for each 1~ sulfur desired in the product. Stated otherwise, from 0.2 to 1.6 parts by weight of magnesium can be employed per each part of xanthate sulfur (the sulEur in the xanthate groups incorporated in the starch). On this basis, the preferred range will be from 0.26 to 0.8 parts by weight of magnesium per part of xanthate sulfur. Products prepared using corresponding weights of any water-soluble magnesium salt gave similar products.
Magnesium oxide, being only very slightly soluble, was ineffective, and magnesium hydroxide is not desirable.

Products containing magnesium ion in the effective amounts indicated above gave increased filtration or centrifugation rates during work-up. The data presented yraphically in Fig. 1 illustrates the accelerated rate of dewatering by filtration. As will be noted, 7 ::
,, ~

: , . . , :
.. . . . .. .. .

~)ti31~3 ~ ~ :
ignificant rate acceleration is obtained in the range from 0.2 ~ :
to 1.6 ~rams magnesium ion per % sulfur, wilile the filtration .. ~ :
advantages maximized in the range of 0.25 to 0.8 grams of magnesium ion per ~ sulfur. Similar.advantages are obtained with respect to dewatering by centrifugation, a more completely dewatered product being obtainable.

After initial dewatering by centrifugat:ion or filtration, it is desirable to further dry the product. It is therefare important that the product has increased flash clrying efficiency.
lOWhen the separated product is introduced into a heated stream of -air, i.t dries rapidly and efficiently to low moisture content ~1-3 The dried product has good room temperature stability. .

Advantages are also provided in the use of the product ;~
for removing heavy metals from a~ueous solutions such as wastewater l!
The product may be applied as a precoat on the ilter sections of l:
a plate and frame filter press. The solution to be treated can then be passed through the filter with a minimum of resistance and pressure drop, while efficiently removing the heavy metal ions.
Alternatively, if the mixed salt xanthate product is mixed with . :
20 the waste water to be treated, it is an advantage that the starch ~ :~
product provides an increased settling rate, thereby maklng it easier to separate the complex of the starch xanthate with the ;.
heavy metals from the supernatant. : .

The magnesium ion can be added anytime before dewatering, ..
namely--(a) before the addition of the crosslinked starch; (b) during the l-hr. xanthation; or ~c) after the l-hr. xanthation is completed. The continuous preparation of ISX would have the ~ .
magnesium ion added before the additon of the crosslinked starch ::
or metered in during the xanthation; however, the best re~ults for 30 batchwise xanthation would utilize additions of magnesium ion after xanthation. The resulting product in either case is a sodium-magnesium ISX having a Na/Mg ratio within the range from 0.5 to 10 mo~sof Na per mol Mg. Products having a Na/Mg ratio , ,. -.. : . .. . . . .

1~3103 - anging from 1-2 mo~sNa per mo~ My were optimum. The sodium dnd the magnesium may form salts with any available oxygen or xanthate in the crosslinked-starch-xanthate. It will be under-stood that the foregoing ratios refer to the alkali metal and magnesium content of the product as recovered after dewatering, and that no-t all of the magnesium or alkali metal content of the recovered product is complexed with the starch xanthate. However, because of the excess of the alkali metal hydroxide in the reaction mixture, and because of the limited amount of the magnesium salt lO employed, the starch xanthate will be present in the product in the form of a mixed salt of the alkali metal (sodium or potassium~
and the magnesium. The product therefore differs from the prior art products which were essentially entirely in the alkali metal form or the magnesium form.

The magnesium ion treatment ylelds products after water washing which contain 20-25% solids and are crumbly for effective flash drying. The preparations which contained about 7~ sulfur and 1-3~ moisture appeared to have better room temperature stability over higher percent sulfur-containing products; however, the Z0 capacity for metal removal is reduced.

. ,~ .
Optimum products for heavy metal removal appear to be the preparations using 15-30 ml. carbon disulfide with 10-20 g.
magnesium sulfate. These products are mixed salts containing both sodium xanthate and magnesium xanthate groups. For use in heavy metal removal the product should be added to the effluent (pH 3 or above) as a solid or slurry allowing the p~ to rise to above pH 7 for optimum removal. The metal-xanthate sludge settles rapidly in the quiescent state in batch-type operations. For continuous flow effluent streams the aid of a clarifier, centrifuge 30 or filter should be used. The sludge obtained from a centrifuge or filter is 50% solids which allows handling ease. After 3 hr.
under ambient conditions, the solid dries to around 90% solids.

Stoichiometric quantities of ISX at a pH above 7 will in most cases reduce heavy metal concentrations to below established - ...,. . ~ .. - .. . . . ~ . . ~
: ~ . ...... : - ~ . . . ,- ., ... .. . . . .

~C~631~)3 -lischarge limits. In some cases, less than stoichiometric quantities of ISX give excellent removal. Heavy metal removal is instantaneous; however, longer contact times are not detri-mental to removal and in most cases increase removal. Salt (NaCl) concentrations of 0-10~ have little influence on the effectiveness of the method.

The effluent after treatment contains only sodium and ..
magnesium ions (Mg, 3-6 mg./l.) from the product. There is no detectable sulfur byproducts unless a decomposecl ISX is used.
10 The use of an ISX product which has decomposed slightly will sometimes turn the effluent pink-amber but at a pH above 8.5 these metal-bearing decomposition products precipitate leaving a c~areffluent. If metal recovery is warranted, the metals can ;;
be released from the ISX by treatment with nitric acid to yield , a concentrated solution of the metal ions. The sludye call also be incinerated to recover the metal oxides. In either treatment, the xanthate group is lost for further use. The nitric acid treatment does allow recovery of the crosslinked starch. If the `
sludge is landfilled, the metal is bound fairly strong and would 20 have less chance to be leached out than a hydroxide sludge. The .:
metal ions are so tightly bound to the ISX that normal eluting agents are ineffective in metal release.
. , The following examples are intended to further describe the invention and are not to be construed as limiting the scope of the invention which is defined by the claims. ~-EXAMPLL l ;

Degrees of swelling were determined for several crosslinked-starches by the following method:
A. Apparatus ~ -~
Mechanical stirrer Stirring blade - triangular glass plate (3/4" base X 4" height) twisted in a spiral connected to a drive shaft (glass rod 8 mm.) at the base of the triangle t ~ -~C~63103 : ~

Centrifuge tube, 40 ml., graduated, Pyrex 93~0 Pipette, 25 ml.
Dishes, evaporating, Coors, approximately 311 diameter Optically clear test tube, 18 mm. X 180 mm.
Glass rod with rubber tip B. Procedure Into a dried, tared centrifuge tube was placed 0.8000 g.
dry basis of the crosslinked starch or ISX to be tested and a sufficient amount of distilled water was added to bring the lO slurry to the 40 ml. mark. The weight of the tube and slurry was noted to the nearest 0.l g.

The centrifuge tube was immersed in a water bath at 95 C.
for 30 min. with stirring at 500 r.p.m. Stirrer should operate in the direction which imparts a downward thrust in the slurry.

~ fter pasting for 30 min., the tube and stirrer were removed, cooled to room temperature, and sufficient distilled water was added to the tube to achieve the noted weight. It is recommended to add the water with a micropipette washing the stirrer as the water is being added. To dislodge particles on the stirrer, a 20 rubber-tipped glass rod is helpful. The sample was stirred 5 min.
at 400 r.p.m. with NO heat to disperse the added water evenly into the paste.

The tube was removed and the stirrer wiped off with the rubber-tipped glass rod to recover as much of the paste as possible.
The tube was centrifuged for 15 min. at 2,500 r.p.m. The tube contained two layers--a supernatant and a sediment.

With the aid of the graduated marks, the volume of the sediment in the tube was determined.

The procedure was repeated with the exception that samples 30 were maintained at 25 to prevent swelling. The sediment volumes for the nonswelled samples were about l.5 ml. Degree of swelling was calculated as follows and reported in Table l:

-- 11 -- :

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1~1631(~3 sediment vol. 95 C. ~ sediment vol. 25 ^legree of swelliny, ~ = sediment vol. 25 Table 1 ~
. , Crosslinked- Crosslinking Volumie, Degree of starch reagent ml. _ swelling, %
Std. (cold) Epichlorohydrin 1.5 ...
A Epichlorohydrin 2.5 67 'r B Phosphorous 2.5 67 oxychloride C Epichlorohydrin 2.6 73 D Epichlorohydrin 3.6 140 E Epichlorohydrin 6.1 306 F Epichlorohydrin 8.2 446 G Epichlorohydrin 2.9 93 ; ~ ~

Crosslinked-starches A through F above were obtained ~ `
commercially. Product G was prepared as follows: 506 g. corn starch were slurried in 650 ml. water containing 7.S g. o~ sodium chloride and 27.8 ml. o~ epichlorohydrin, and 30 g. KOH in 100 ml.
water were added in 4-ml. portions every 10 min. The slurry was 20 stirred for 20 hr., neutralized with HCl, filtered, washed -successively with water, acetone and ether, and oven dried. Degree of swelling was determined as above.

:.^. , Crosslinked-starch A (Table 1) (100 g.) was slurried in water (435 ml.), and sodium hydroxide (45 g.) in water (125 ml.) was added. This mixture was stirred 30 min. Carbon disulfide (30 ml.) was added and the mixture was stirred 1 hr. in a covered beaker. Magnesium sulfate (19 g.) in water (250 ml.) was added and the mixture was allowed to stir an additional 5 min. The slurry was filtered through a B~chner funnel using Whatman No. 54 filter 30 paper and the solid was washed with water (1,000 ml.). The solid (75% H2O) was then washed with acetone and ether. After drying -for 2 hr. under vacuum, the product was analyzed. Yield 120 g.;
S, 9.62%; H2O, 8.92%; ash, 12.89%.

~ 12 -- , - . . . , , . , ~

1063:~03 , : ~
EXAMPI,ES 3 9 Crosslinked-starches A and D (Table 1) were xanthated as described in Example 2. ~pproximately 2 g. magnesium sulfate ~ '~
for each l~S desired in the final product was used. The products were flash dried with a laboratory ~enco Vertical Pneumatic Dryer. Percent sulfur was determined by the Schoniger procedure in most cases. Some interference was noted occasionally from the magnesium and, when this occurred, the percent sulfur was determined gravimetrically. Moisture analysis was run at 25 ~.
under vacuum for 2-3 hr. Percent ash includes sodium and lOmagnesium of xanthate and bound alkali in product. Sodium and magnesium contents of the products were determined by treating a 0.25-g. sample with lN nitric acid (45 ml.) to remove all the sodium and magnesium. The filtrates were diluted to 1 1. and the sodium and magnesium concentrations were determined on a Varian Techtron AA120 spectrophotometer. The capacities for the products were determined by the following formulas~

% S = 6400 D.S. , meq/g. = D.S. ~1,000) , 162 - D.S. + 99.5 D.S. 162 ~ D.S. (99.5) % S . ~.
or meq/g. =6.412 In Examples 8 and 9 the magnesium sulfate in water (180 ml.) was added 45 sec. after the carbon disulfide. Weights and volumes of reactants and analysis of the final products are disclosed in Table 2. The yellow-tan products were stored in a cool, dry pl ace f or maximum ef f ectivene ss .

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" ~'', '' 1C~631()3 Crosslinked-starch A (100 g.) was slurried in water ~435 ml.) and potassium hydroxide (63 g.) in water (125 ml.) was added. This mixture was stirred 30 min. Carbon disulfide (30 ml.) was added and the mixture was stirred 1 hr. in a co~ered beaker.
Magnesium sulfate (19 g.) in water (200 ml.) was added and the mixture was allowed to stir an additional 5 min. The slurry was filtered through a Buchner funnel using Whatman No. 54 filter paper and the solid was washed with water (1,000 ml.). The solid (80 water) was flash dried. Yield: 125 g.; S, 10.13%; H2O, 5.92%; ~
10 ash, 33.33~; K, 27.7 mg.; Mg, 7.74 mg.; K/Mg, 3.58; capacity = ;
1.56 meq/g. ~

:. :' Commercial corn starch (100 g.; 10% H2O) was slurried in water (150 ml.) containing sodium chloride (1.5 g.) and epichloro-hydrin (7.0 ml.). To this slurry was added potassium hydroxide (6 g.) in water (40 ml.) slowly over 15 min. and the mixture was allowed to stir for 16 hr. The suspension, now containing highly crosslinked-starch, was diluted with water (245 ml.) and was treated with sodium hydroxide (45 g.) in water (125 ml.). After 30 min. carbon disulfide (15 ml.) was added and the mixture was 20stirred 1 hr. in a covered beaker. Magnesium sulfate (11 g.) in water (200 ml.) was added and the mix~ure was stirred an additional 5 min. The mixture was worked-up as in Example 2. Yield: 122 g.;
S, 5.58%; H2O, 6.17~; Ash, 10.94%; Na/Mg, 1.41.

EXAMPLE_12 Crosslin~ed-starch A (Table 1) (20 lb., d.b.) was slurried in water (80 lb.) and magnesium sulfate (3.61 lb.) was added. The slurry was pumped through a Baker Perkins Flowmaster Rotofeed ~ ;
(7-1/2") at 890 g./min. and 28 C. The sodium hydroxide (4.66N, 24 1.) was metered in at 470 ml./min. and the carbon disulflde (3.32 1.) at 65 ml./min. The slurry was pumped ~hrough in 50 min.
30and after 30 min. in a holding tank, water (10 gal.) was added iL5 . . . ~ . .
.

~ 3~11)3 ~ r easier feeding to the centrifuge. The mixture was centrifuged in a Tolhurst Centrifuge (26"-2,400 r.p.m.) at 650 r.p.m. and then washed with water (26.5 gal.). The cake was dewatered to 27% solids at 1,500 r.p.m. The cake was flash dried and gave the following analysis: S, 9.14~; ash, 14.06%; H2O, 3.16~.

Solutions (1,000 ml.) containing the individual metals at the indicated concentrations were treated with the indicated amounts of ISX of Example 6 at pH 3.7. Solutions were stirred for 5-60 min. at a final pH of 8.9. After filtration, the residual lOmetals were determined by a Varian Techtron AA120. The theoretical weight of ISX for a divalent metal is 0.64 g. The results are set forth in Table 3 below. ~ ?

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Claims (9)

The Claims

1. The process of preparing a starch xanthate product wherein crosslinked granule starch is xanthated in an aqueous slurry containing excess sodium or potassium hydroxide, characterized by incorporating an amount of a water-soluble magnesium salt in said slurry prior to dewatering the xanthated starch which provides from 0.2 to 1.6 parts by weight of magnesium per each part by weight of xanthate sulfur, and dewatering the xanthated starch by filtration or centrifugation to obtain a product comprising a mixed alkali metal (sodium or potassium)-magnesium salt of cross-linked starch xanthate.

2. Products produced according to the process of Claim 1 and further characterized by containing from 0.5 to 10 moles of alkali metal per mole of magnesium.

3. The process of Claim 1 in which the amount incorporated of said magnesium salt provides from 0.26 to 0.8 parts by weight of magnesium per each part by weight of xanthate sulfur.

4. Products produced according to the process of Claim 3 and further characterized by containing from 1 to 2 mobs of alkali metal per mole of magnesium.

5. The process of Claim 3 in which said magnesium salt is magensium sulfate.

6. The process of Claim 3 in which said product is de-watered by filtration.

7. The process of Claim 3 in which said crosslinked granule starch is xanthated to a degree of substitution (D.S.) of 0.1 to 0.35.

8. The process of Claim 7 wherein the crosslinked granule starch employed for said xanthation has a degree of swelling in water at 95°C of from 65 to 75%.

9. Products produced by the process of Claim 8.