THE INFLUENCE OF RECIRCULATING WATER IMPURITIES ON THE PERFORMANCE OF CALCIUM PHOSPHATE INHIBITING POLYMERS

Transcription

1 NACE THE INFLUENCE OF RECIRCULATING WATER IMPURITIES ON THE PERFORMANCE OF CALCIUM PHOSPHATE INHIBITING POLYMERS Zahid Amjad, PhD Digen Butala, PhD and Jeff Pugh Noveon, Inc. (formerly BFGoodrich Performance Materials) 9911 Brecksville Road Cleveland, Ohio ABSTRACT Many factors, including ph, temperature, make-up water quality, and heat exchanger metallurgy, influence the performance of polymeric inhibitors in treating recirculating cooling water systems. The availability of good quality make-up water and the imposition of stringent wastewater discharge regulations have forced many cooling systems to operate at increasingly higher cycles of concentration. The severity of these operating conditions often results in waters that have higher scale formation potential. Presented here is information regarding the influence of impurities, such as suspended matter and metal ions, on the performance of polymeric inhibitors used in phosphate-based treatment programs. Keywords: calcium phosphate, cooling water, polymers, scale, metal ions INTRODUCTION Historically, water is one of the most common heat transfer fluids used in industrial processes. The unique combination of high thermal conductivity, heat capacity, and large useable temperature range make water ideally suited as an heat transfer fluid for industrial processes. Governmental regulations and economic considerations often dictate that cooling tower operators increase the cycles of concentration of their cooling water. When this happens, the ionic constituency of the cooling water may increase dramatically and the solubility of certain scale forming salts may be exceeded. As supersaturation is achieved, thermodynamics dictates that precipitates will form. Deposit control polymers (DCPs)

2 including poly(acrylic acid) and acrylate-based co- and terpolymers are often used in water treatment applications to reduce the formation of these scales. These DCPS affect the scale formation kinetics by extending the precipitation induction time beyond the holding time of the tower 2 which is a property known as threshold inhibition. These DCPS have also been shown to modi~ the crystal structures such that the precipitates formed are less adherent and to disperse particles that would otherwise agglomerate. Phosphates and phosphonates are essential components of stabilized-phosphate and all-organic cooling water treatment (C WT) programs. However, the performance of multifunctional DCPS is the key to the efficacy of these CWT programs. These high performance DCPS control the thickness of the calciumphosphate film on metal surfaces and prevent precipitation of the calcium-phosphate and calciumphosphonate salts in the recirculating water.2 3 4Various polymers are used in these CWT programs to minimize scale formation and for deposit control. The performance of polymers used in recirculating cooling water has been shown to depend on the quality of the water in the system. Factors governing the performance of polymers can be divided into two distinct categories: (1) those that affect the volubility of the scale-forming salts and (2) those that affect the action of the polymer. Solution ph affects the deprotonization of polymers, the affinity of polymers towards ionic species, and the adsorption of polymers onto growing crystal surfaces. Solution ionic strength also affects polymer performance.5 Additionally, all open cooling towers using natural waters contain certain level of contaminants such as transition metal ions and particulate matter can affect deposit control polymer performance. Transition metal ions are known to significantly effect the performance of these polymers This is a particular concern because metallic materials are typically the materials of choice for cooling tower piping and heat transfer surfaces. All open cooling towers using natural waters contain particulate contaminants (e.g., clay) which adsorb DCPS and thereby reduce the availability of DCPS for the other desired functions. Traditionally, CWT program applications consider the adverse impact of iron. However because of increasingly stringent CWT program operating conditions, it is important to consider the effect of other metal ions (i.e., copper, manganese, zinc) and contaminants (i.e., clay, cationic polymers). These metal ions effect the morphology and kinetics of calcium carbonate, calcium sulfate, and calcium phosphate scale formation. g- In a previous publication,6 the effect of a cationic polymer on calcium phosphate inhibition by DCPS was presented. This paper specifically addresses the effect of water contaminants (e.g., metal ions, clay) on calcium phosphate inhibition by DCPS. Quantification of effect of these on DCPS will help facilitate the optimization of CWT programs. EXPERIMENTAL The experiments described in this paper were designed to correlate to field situations and to reflect conditions of actual operating systems but to maintain the experimental control of a laboratory study. This investigation examines the influences of common contaminants (e.g., particulate silt and clay, metal ions) on calcium phosphate inhibiting polymers. The DCPS used in this study have shown to be effective in retarding calcium phosphate precipitation. The chemicals used to makeup the solutions were Fisher Scientific ACS reagent grade and the DCPS were commercial products. Class A glassware was used for all experiments. Polymer concentrations are given on an active polymer basis. Stock solutions of known concentrations of calcium chloride, sodium phosphate, hydrochloric acid, sodium hydroxide, and various polymers were prepared and used to

3 makeup test solutions. The dilution water used was double deionized and distilled. A Metrohrn- Brinkrnann ph-stat unit equipped with a combination electrode was used to maintain the experimental solution ph. The ph electrode was calibrated before every experiment with standard buffers. The test solution temperature was maintained to *1 C by passing controlled water through the outer jacket of the jacketed reaction vessel. The test solution was made by the slow addition of the phosphate stock solution with stirring to the desired water. The polymer and other ionic constituents were added and the solution ph was adjusted, if necessary, after a 30-minute equilibration period. The calcium stock solution was added, making up the total volume to 600 ml. For all the experiments the reaction period was fixed at 22 hr. During each experiment, the test solution ph was maintained (within ph units) at the desired level using the ph-stat unit. Unless specified, the standard test conditions for the calcium phosphate threshold inhibition were 140 ppm [Ca], 9 ppm [POd], ph 8.5, 50 C, and 22 hr. The reaction progression was determined by spectrophotometric analysis of filtered (0.45 micron) aliquot of the test solution for the phosphate ion. The efficacy of the polymer was calculated as percent inhibition as given in equation 1. TI = [P04]X,,=22- [p04]0,t=22 x 100 %0 (1) [po41t=o - [p04]0,t=22 where: TI D 041,=0 [p04]x,&22 [p04]0,t=22 Threshold inhibition, YO. Phosphate ion concentration at the beginning of the experiment = Phosphate ion concentration in the test solution after 22 hr Phosphate ion concentration in the control experiment after 22 hr RESULTS AND DISCUSSION Environmental regulations are the key driver for the increase use of all-organic (phosphate and phosphonate based) CWT programs. High performance DCPS are used in all organic CWT programs to inhibit/disperse phosphate and phosphonate based scales.2-4 The DCP concentrations required to inhibit the formation and precipitation of calcium phosphate is highly dependent on solution saturation, the precipitating salt form, the system residence time, the water impurities, and the inhibiting polymer characteristics. The solution saturation is a function of temperature, ph, ionic concentrations, and pressures. The water impurities could be metal ions or suspended solids. DCP characteristics such as, functional groups, molecular weight, and structural modifications affect the ability of DCPS to inhibiting/dispersing calcium phosphate. As described in the Experimental section, several experiments were conducted with different DCPS in the presence of different water impurities. The focus of the experimental work herein is the differentiation of the performance of acrylate co- and terpolymers. However, occasionally included herein are data for the performance of other polymers. The DCPS used in these tests were commercially available acrylate homo-, co-, and terpolymers. Table 1lists the DCPS evaluated in this study.

4 Effect of Polymer Dosage at Standard Conditions The ability of polymer to inhibit calcium phosphate formation is very important aspect of phosphate and phosphonate-based water treatment programs. Figure 1 shows threshold inhibition as fi.mction of polymer dosage for polymer A, polymer B, and polymer C. A 10 ppm dosage of polymer A is required to inhibit (290 A TI) the formation of calcium phosphate whereas only 7.5 ppm of polymer B is required to achieve the same performance. However, even at a 15 ppm dosage, the calcium phosphate inhibition for polymer C (polyacrylic acid) is only 10%. Comparison of the three performance curves in Figure 1 clearly shows the superior calcium phosphate inhibition of polymer B (terpolymer) as a function of dosage. The incorporation of co-monomers containing sulfonic acid groups improves the inhibiting power of the DCPS. The balance of this paper makes frequent references to the threshold inhibition curves for polymer A and polymer B in Figure 1 for comparison with the performance of polymers A and B in presence of the various water impurities. These comparisons illustrate the effect of water impurities on calcium phosphate inhibition of polymers. Effect of Metal Ions on Calcium Phosphate Inhibition Metal ions present in cooling water systems may be contributed by corrosion by-products, treatment program components, and water impurities. Metal ions significantly effect the calcium phosphate inhibition performance of polymers. 1 4 G-8 Therefore, it is important to quantify the effect of different metal ions such as iron, copper, manganese, and zinc on the performance of polymers used in the cooling water treatment programs. Effect of Iron (111). Soluble iron, the ferrous ion, is often encountered in natural water systems either from the water itself at low concentrations (usually less than 3 ppm) or as a result of corrosion of the iron piping, well heads, or other vessels in the system. On oxidation, the ferric ion may tie up or deactivate DCPS. Co- and terpolymers are touted as having excellent tolerance to iron (III). It is important to evaluate the efficacy of polymers to inhibit calcium phosphate in presence of iron. Several earlier studies have addressed the effect of iron on efficacy of different polymers.g 8For this study, iron (III) ranging from Oto 3 ppm was introduced to the test solution as a ferric chloride solution following temperature stabilization but prior to ph adjustment and before the introduction of the calcium solution. Figure 2 shows the effect of iron (III) on the performance of polymer A for calcium phosphate inhibition as a function of polymer dosage. The effect of iron (III) on calcium phosphate inhibition of polymer B is illustrated in Figure 3. Comparing the threshold inhibition vs. dosages for polymers A and B in Figure 1 with Figures 2 and 3 shows that the presence of 3 ppm of iron (III) necessitates higher polymer dosages to achieve the same performance. Acrylate polymers form a complex with the iron ion (are tied up by iron) unlike the momentary association of the polymer with the scale forming species. The polymer demand by the metal ion complexation is in addition to the amount required for threshold inhibition. In the presence of the iron, 15 ppm polymer A and more than 10 ppm of polymer B are needed to successfully inhibit the calcium phosphate precipitation. It is important to note that typically 33 /0 more polymer B and 50% more polymer A were required to inhibit calcium phosphate in the presence of 3 ppm iron (III). The results clearly show that polymer B is more tolerant of iron (III). Similar results have been previously reportedb for calcium phosphate inhibition of polymer A and polymer B in presence of iron (III) under highly stressed test conditions.

5 Figure 4 shows a comparison of the iron tolerance of several other DCPS used in CWT applications. These tests were run under the same conditions as those previously described and with 10 ppm of each polymer. The calcium phosphate inhibition of polymer A and polymer E in presence of 2.5 ppm iron is reduced to below 20 /0. Where as only slight reductions in calcium phosphate inhibition of polymer B and polymer D were observed in the presence of 2.5 ppm iron. These results clearly show that terpolymers demonstrate a greater tolerance for the iron (III) ion. Effect of Manwmese. Manganese is occasionally an impurity of water sources. The presence of manganese in cooling water can lead to deposition and associated corrosion problems. Polymers are used in many cooling water treatment programs to control manganese deposition. It is believed that polymers solubilize manganese ion and disperse manganese oxide/hydroxide particles.10 12The results presented here quanti~ the effect of manganese on calcium phosphate inhibition of various polymers. Manganese was introduced to the test solution after temperature stabilization but before ph adjustment and the addition of the calcium solution. For all cases the manganese concentration was 5 ppm. The effect of manganese on calcium phosphate inhibition of polymer A and polymer B is shown in Figures 5 and 6, respectively. Comparison of the threshold inhibition curves for both the polymers indicates almost similar slopes in presence and absence of manganese. This observation leads to believe that a stoichiometrically proportional amount of polymer is required to complex with the manganese before free polymer can interact with the calcium to inhibit the scale formation. In both cases, polymer dosages must be increased by 20% or more to achieve >90% calcium phosphate inhibition in presence of 5 ppm manganese ion. Calcium phosphate inhibitions of different polymers in the presence of 5 ppm manganese ion are shown in Figure 7. These tests were run using the standard conditions (previously described) and 10 ppm dosages of each DCP. The results clearly indicate that the performance of polymer A and polymer E is dramatically reduced even in presence of 5 ppm manganese ion. The performance of terpolymers (polymers B and D), is only slightly affected by the presence of 5 ppm manganese. These results again show the superior efficacy of terpolymers in stabilizing metal ions. Effect of Zinc. Zinc salts are often added to CWT programs for corrosion control. Zinc ion can also be introduced to circulating water by the corrosion of galvanized cooling towers. As with other metal ions, it is important to quanti~ and understand the effect of zinc on calcium phosphate inhibition of polymers.lq Zinc was introduced to the test solution at 5 ppm concentrations after temperature stabilization but before ph adjustment and the introduction of the calcium solution. The effect of zinc on calcium phosphate inhibition of polymer A and polymer B is depicted in Figures 8 and 9, respectively. In both cases, zinc by itself does not provide any significant calcium phosphate inhibition (<1 0 /0TI). However, both Figures 8 and 9 indicate that the presence of zinc greatly enhances the calcium phosphate inhibition of polymers A and B. The threshold inhibition curves are shifted towards reduced polymer dosages in presence of 5 ppm zinc. In case of polymer A, dosage reduction of more than 3 ppm is observed, whereas in case of polymer B, dosage reduction of almost 2 ppm is observed to achieve >90?40TI. From these results it appears that copolymer, polymer A, containing higher amount of carboxylic groups provides more synergy than the terpolymer, polymer B. Additional testing in our laboratory with the polymers containing different levels of carboxylic groups supports this observation. The synergistic effect of zinc on calcium phosphate inhibition of DCPS is very clear in these tests and agrees with results of the calcium phosphate crystal growth inhibition characteristic of

6 zinc as reported in the literature. 14A similar effect of zinc on calcium carbonate has also been reported in the literature.9 crystal growth inhibition Effect of Copper. A low level of copper is a common impurity in cooling water systems. Normally, copper is picked up by the cooling water from copper tubing or as a corrosion product from copper containing metals such as brass. Copper salts may also be used as an algaecide in open cooling basins. Copper ions may tie up polymers similar to iron, thereby reducing the effectiveness of the program. In these experiments, quantifying the effect of copper on acrylate polymers was determined by adding copper as a copper nitrate solution to the test solution and measuring calcium phosphate inhibition as noted above. The calcium phosphate inhibition of polymer A and polymer B in presence of 5 ppm copper are given in Figure 10 and Figure 11, respectively. The effect of copper on the performance of DCP as calcium phosphate inhibition is not as detrimental as that of iron (III). However, higher polymer dosages are required to achieve 290 /0 TI in the presence of 5 ppm copper such that the threshold calcium phosphate inhibition curves are shifted to the right. Almost 3 ppm (30 /0)more polymer A is required where as only 1.5 ppm (20?40)more polymer B is required. Terpolymers appear to be much more efficient in stabilizing the copper ions than the copolymers. Figure 12 compares the calcium phosphate inhibition of polymers A, B, and E without metal ion, in presence of 5 ppm zinc, and in presence of 5 ppm copper, The data show the results for 10 ppm dosages of polymers A and E in comparison with 7.5 ppm dosages of polymer B. All three polymers perform well in absence of metal ions and in presence of 5 ppm zinc. However, it is important to note that 2.5 ppm (25%) less polymer B is required to achieve the same performance. In the presence of 5 ppm copper ion, 10 ppm of polymer A performs poorly whereas very good performance was obtained using 10 of ppm polymer E or 7.5 ppm of polymer B. It is noteworthy that polymer B at a 25% lower dosage performs better than polymer E. Effect of Suspended Solids on Calcium Phosphate Inhibition Polymers are known to adsorb onto particles that may be present in the water. The adsorption of the polymers onto particles and the resultant interaction between particles is the mechanism of dispersion. However when a polymer is tied up dispersing particles, it is not as available to inhibit the formation of scale forming salts. In addition, suspended solids could act as nuclei for the formation of calcium phosphate. The magnitude of this effect was tested with Dixie Clay. Effect of Clay Particles. Dixie clay is a kaolin clay (aluminum silicate hydrate) that has a large surface area (27 m2/g BET surface area - Micromeritics ASAP 2400). Because of its high surface area, it is reasoned to be more detrimental to the polymer inhibition and was therefore used as a model suspended particle. Experiments were run at the standard conditions with varying concentrations of the clay to determine the loss of polymer efficacy. The correct quantity of clay (to give 50 to 250 mg/l clay in the final solution) was added before the calcium chloride solution addition initiates the experiment. This range of particulate concentrations covers more than is usually seen in an operating cooling tower. This range will allow us to model the effect of the clay on the polymer. Figure 13 shows the results with and without Dixie Clay and either 10 ppm polymer A or 7.5 ppm polymer B. The presence of 50 mg/l clay slightly reduces the efficacy of polymer A but has no effect on

7 performance of polymer B. Increasing the particulate concentration to 100 mg/l affects the performance of both polymers. Increasing to 250 mg/l clay significantly impacts the calcium phosphate threshold inhibition of both polymers. Figure 14 illustrates the calcium phosphate inhibition of polymer A (1Oppm), polymer B (7.5 ppm), and polymer E (1Oppm) in presence of 100 mg/l clay. Polymer A and polymer E at 10 ppm dosage level provide almost same (=65VO) calcium phosphate inhibition in presence of 100 mg/l. However, polymer B, even at a 25 % lower dosage (7.5 ppm), provides excellent (85Yo) calcium phosphate inhibition in presence of 100 mg/l). Figure 15 show the results for polymers A and B which were previously reportedl for a highly stressed system. In this case, the calcium, phosphate, and polymer concentrations were increased. The results parallel those in Figure 13 wherein polymer B at a lower dosage outperforms polymer A. SUMMARY Cooling waters contain a number of contaminants that may be antagonistic to acrylate polymers used in the water treatment programs. By understanding the effect of these contaminants on the polymer performance, the CWT program technologists can compensate for the effects of these contaminants. The experiments described in this paper suggest several conclusions noted below. Further study is in progress and will be presented in the future The presence of iron (III) in cooling water is detrimental to the calcium phosphate inhibition of acrylate polymers. Copolymers containing sulfonic acid have a certain tolerance to and can stabilize the iron (III) ion. The amount of additional polymer that will be required depends on how well the polymer can stabilize the iron. Manganese ion and copper ion are antagonistic to the performance of acrylate-based DCPS but the adverse impact is not as great as with iron. Increasing polymer dosages can compensate for the presence of manganese ion and/or copper and result in acceptable performance (>90 XOTI). The zinc ion exhibits a synergy with the polymer allowing enhanced calcium phosphate inhibition at lower polymer dosage than would be expected to be necessary. Suspended particles adversely impact the performance of polymers because of the adsorption of polymers on particulate matter thereby reducing the available polymer for threshold inhibition. Terpolymers seem very resilient to the presence of clay in water. Overall, terpolymers appear to have better performance due to their superior tolerance of metal ions and excellent calcium phosphate inhibition properties. REFERENCES 1. R. W. Zuhl, Z. Amjad, The Role of Polymers in Water Treatment Application and Criteria for Comparing Alternatives, Association of Water Technologies 1993, Sixth Annual Convention, Las Vegas, NV, Nov-1993.

8 2. J.E. Hoots, G.A. Crucil, Role of Polymers in the Mechanisms and Performance of Alkaline Cooling Water Programs, CORROSION/86, Paper No. 13 (Houston, TX, NACE International, 1986). 3. W.F. Masler, Z. Amjad, Advances in the Control of Calcium Phosphonate with Novel Polymeric Inhibitors, CORROSION/88, Paper No. 11 (Houston, TX, NACE International, 1988). 4. R.W. Zuhl, Z. Amjad, W.F. Masler, A Novel Polymeric Material for Use in Minimizing Calcium Phosphate Fouling in Industrial Cooling Water Systems, Paper No. TP 87-7, Cooling Tower Institute, Houston, TX. 5. Z. Amjad, Seeded Growth of Calcium Containing Scale Forming Mineral in the Presence of Additives, CORROSION/88, Paper No. 421 (Houston, TX, NACE International, 1988). 6. Z. Amjad, J. Pugh, J.F. Zibrida, R.W. Zuhl, Polymer Performance in Cooling Water: The Influence of Process Variables, CORROSION/96, Paper No. 160 (Houston, TX, NACE International, 1996). 7. A. Marshall, B. Greeves, The Effect of Water Quality on the Performance of Extended Phosphate Technology, CORROSION/86, Paper No. 399 (Houston, TX, NACE International, 1986). 8. L. Dubin, K,E. Fulks, The Role of Water Chemistry on Iron Dispersion Performance, CORROSION/84, Paper No. 118 (Houston, TX, NACE International, 1984). 9. P. Coetzee, M. Yacoby, S. Howell, S. Mubenga, Scale Reduction and Scale Modification Effects Induced by Zn and Other Metal Species in Physical Water Treatment, Water SA, Vol. 24, No. 1, p. 77, B. Pernot, M. Euvrard, P. Simon, Effects of Iron and Manganese on the Scaling Potentiality of Water, J Water SRT-Aqua, Vol. 47, No. 1, p , T.J. Young, The Proper use of Modem Polymer Technology in Cooling Water Programs, Association of Water Technologies 1990, Third Annual Convention, Lake Buena Vista, FL, Nov K. Fivizzani, L. Dubin, B. Fair, J.E. Hoots, Manganese Stabilization by Polymers for Cooling Water Systems, CORROSION/89, Paper No. 433 (Houston, TX, NACE International, 1989). 13. H. Ohtaka, T. Kawamura, Y. Furukawa, Zinc and Phosphate Scale Inhibition by a Newly Developed Polymer, CORROSION/89, Paper No. 432 (Houston, TX, NACE International, 1989). 14. P. Koutsoukos, Influence of Metal Ions on the Crystal Growth of Calcium Phosphates, Calcium Phosphates in Biological and Industrial Systems, Edited by Z. Amjad, Kluwer Academic Publishers, p. 145, J.F. Zibrida, R. Thorgeson, E. Mistretta, Factors Influencing Cooling Water Polymer Selection, Water Soluble Polymers: Solution Properties and Applications Symposium, American Chemical Society National Meeting, Las Vegas, NV, 7 to 1l-Sep-1997.

9 TABLE 1 Deposit Control Polymers Evaluated Polymer Composition A Acrylic acid : Sulfonic acid copolymer B Acrylic acid : Sulfonic acid : Sulfonated styrene terpolymerb c Acrylic acid homopolymerc D Acrylic acid : Sulfonic acid : Non-ionicd E Acrylic acid: Sulfonated styrene copolymer a: K-775AcrylateCopolymer b: K-798AcrylateTerpolymer c: K-752Polyacrylate d: CompetitiveTerpolymer e: CompetitiveCopolymer

10 + PolymerA PolymerB PolymerC [Ca] = 140 ppm, [POJ = 9 ppm PH = 8.5, T= 50 C, t =22 houre o Polymer Dosage (ppm) FIGURE 1. Effect of polymer dosage on calcium phosphate inhibition. 100%. - 90% -r- +~ E 30% ? / 3 ppm imn 10% -- o% ~ O [Ca] = 140 ppm, [PO~ = 9 T=50 C, t=22hours Polymer A Dosage FIGURE 2. Calcium phosphate inhibition of copolymer in the presence of the iron (III) ion.

11 FIGURE 3. Calcium phosphate inhibition of terpolymer in the presence of the iron (III) ion. Threshold Inhibition (%) Polymer A Polymer B Polymer D Polymer E [Ca] = 140 ppm, [PO4] = 9 ppm ph = 8.5, T = 50 o C, t = 22 hours 10 ppm Polymer 0 ppm Fe 1 ppm Fe 2.5 ppm Fe FIGURE 4. Calcium phosphate inhibition of different polymers in the presence of the iron (III) ion.

12 100% ~. s 30% % -- 10=%-- o% - [Ca]=140 p~m, [POj = 9 p~m DH= 8.5, T =50 C, t =22 houcs Polymer A Dosage FIGURE 5. Calcium phosphate inhibition of copolymer in the presence of the manganese ion. 100 /6 90% 80% / 5 ppm manganesa 20% 1o% -- o% o [Ca] = 140 ppm, [PO,]= 9 T = 50 C, t =22 hours Polymer B Dosage FIGURE 6. Calcium phosphate inhibition of terpolymer in the presence of the manganese ion.

13 .4 nn IUu Oppm M 5ppmlvh Polymer A Polymer B Polymer D Polymer E [Ca] = 140 ppm, [PO,]= 9 ppm ph = 8.5, T = 50 C, t = 22 hours 10 ppm Polymer FIGURE 7. Calcium phosphate inhibition of different polymers in the presence of the manganese ion. 100% 90% - 80% - 5 ppm zinc ~ II2I [Ca] = 140 ppm, [PO,]= 9 ppm PI-I=8.5, T = 50 C, t = 22 houra Polymer A Dosage FIGURE 8. Calcium phosphate inhibition of copolymer in the presence of the zinc ion.

14 i 00% 90% 80% 5 ppm zinc * 70% L c g 60% ṃ - S = 50% = o 40% c 0al k 30% + 20% 1o% 07 0 o Q In. [Ca] = 140 ppm, [PO.]= 9 ppm Polymer B Dosage ph = 8.5, T=50 C, t = 22 houre FIGURE 9. Calcium phosphate inhibition of terpolymer in the presence of the zinc ion. 100% % & 70% c o ~ 60% ṇ - = = 50% ~ ~ 40% Lo al E 30% 1-20% 0% t! [Ca] = 140 ppm, [PO,]= 9 ppm ph=8.5, T=50 C, t=22hours Polymer A Dosage FIGURE 10. Calcium phosphate inhibition of copolymer in the presence of the copper ion.

15 100% 90% 80% 7 & 70% ppm copper 5 := 60?4 -- ṇ -.c = 50% -- ~ ~ 40% - w al k 30= % -- 10% [Ca]=140 ppm, [P04] = 9 ppm Polymer B Dosage PH = 8.5, T = 50 C, t = 22 hours FIGURE 11. Calcium phosphate inhibition of terpolymer in the presence of the copper ion. 100?40~-- 90?40+ 80% 70% 60% t 50?40 40?J0 30% 20% 1O?AO 0% 1 O ppm Metal 5 ppm Zn 5 ppm Cu [Ca] = 140 ppm, [PO~ = 9 ppm PH = 8.5, T= 50 C, t = 22 houra 10 ppm Polymer A 7.5 ppm Polymer B 10 ppm Polymer E FIGURE 12. Calcium phosphate inhibition of co- and terpolymers in the presence of copper and zinc ion.

16 No Clay 50 mg/1clay mg/1 Clay 250 mg/1 Clay [Ca] = 140 mg/1, [POd] = 9 mg/i 10 ppmpolymer A ph = 8.5, T= 50 C, t = 22 hours 7.5 ppm Polymer B FIGURE 13. Calcium phosphate inhibition of co- and terpolymer in the presence concentrations of Dixie Clay. of varying 100% ~ 90% 1 70?40 80% 60% 50% 40!40 30% 20% -- 1o% o% No Clay 100 ppm Clay 4 [Ca] = 140 ppm, [POJ = 9 ppm ph = 8.5, T= 50 C, t = 22 hours 10 ppm Polymer A 7.5 ppm Polymer B 10 ppm Polymer E FIGURE 14. Calcium phosphate inhibition of co- and terpolymers in the presence of 100 ppm of Dixie Clay.

17 100 I g 90 ; Q.- 60 s g 50 g 40- z 30-- m g 20-.s *I o. No Clay 50 mg/i Clay 100 mg/1clay 250 mg/1clay [Ca] = 240 mg/1, [PO,] = 15 mg/1 25 ppm Polymer A ph = 9.0, T = 50 C, t = 22 hours 17.5 ppm Polymer B FIGURE 15. Calcium phosphate inhibition of co- and terpolymer in the presence concentrations of Dixie Clay under highly stressed conditions. of varying