Technological properties of phosphogypsum binder obtained from fertilizer production waste

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International Scientific Conference “Environmental and Climate Technologies”, CONECT 2018 International Scientific Conference “Environmental and Climate Technologies”, CONECT 2018

Technological properties ofSymposium phosphogypsum binder obtained from The 15th Internationalof on District Heating and obtained Cooling Technological properties phosphogypsum binder from fertilizer production waste fertilizer production Assessing the feasibility of using thewaste heat demand-outdoor Girts Bumanis*, Jelizaveta Zorica, Diana Bajare, Aleksandrs Korjakins

temperature function for aZorica, long-term districtAleksandrs heat demand forecast Girts Bumanis*, Jelizaveta Diana Bajare, Korjakins

Department of Building Materials and Products, Institute of Materials and Structure, Riga Technical University, Kalku iela 1, Riga, LV-1658, Latvia Department of Building Materials a,b,c and Products,aInstitute of Materials a and Structure, Riga b Technical University, Kalku c iela 1, Riga, LV-1658, c Latvia

I. Andrić

*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre

a

IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Dihydrate phosphogypsum (PG) from phosphate fertilizer production plant was considered as secondary raw material to produce gypsum binder. XRD was used characterize mineral composition ofplant raw material before and after heat treatment, as to well as for Dihydrate phosphogypsum (PG)tofrom phosphate fertilizer production was considered as secondary raw material produce hardenedbinder. samples. properties of obtained binder were regarding to the gypsum XRDTechnological was used to characterize mineral composition of rawdetermined material before and after heatdehydration treatment, astemperature well as for between 100 °C andTechnological 180 °C and optimal heat treatment parameters for PGdetermined were foundregarding to obtain PG hemihydrate. Setting time of hardened samples. properties of obtained binder were to the dehydration temperature Abstract binder lime treatment additive parameters or two different plasticizers and rosinSetting resin time based). betweenwas 100 tested °C andby 180adding °C and slacked optimal heat for PG were found to(lignosulfonate obtain PG hemihydrate. of Compressive strength and moisture content was determined for 2 h and 14 d old samples. Results indicate that higher heat binder was tested by adding slacked lime additive or two different plasticizers (lignosulfonate and rosin resin based). District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the treatment temperature of PG reduce time towas decompose to hemihydrate the initial that setting time of Compressive strength and moisture content determined for 2 require h and 14 dand oldslightly samples.increase Results indicate higher greenhouse gas emissions from the building sector. These PG systems high investments which are returned through theheat heat obtained binder. Addition of climate plasticizer water-PG from 0.80 toand 0.43slightly anddemand the setting time was setting increased with treatment temperature of PG reduce conditions timereduced to decompose PGratio to hemihydrate increase initial time of sales. Due to the changed and building renovation policies, heat in the the future could decrease, lignosulfonate plasticizer. Early agereduced (2 h) strength of binder was from to 15and MPathe andsetting after 14 d hardening it reached obtained binder. Addition of plasticizer water-PG ratio from 0.80 0.1 to 0.43 time was increased with prolonging thebased investment return period. 2.5 29 MPa, giving a promising results PGofas secondary raw material for production. lignosulfonate based plasticizer. Early ageconsidering (2 feasibility h) strength ofusing binder from 0.1 to 15 binder MPatemperature and after 14function d hardening it reached Thetomain scope of this paper is to assess the thewas heat demand – outdoor for heat demand 2.5 to 29 MPa, giving a promising results considering PG as secondary raw material for binder production. forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©buildings 2018 Thethat Authors. Published by Elsevierperiod Ltd. and typology. Three weather scenarios (low, medium, high) and three district vary in both construction © 2018 2018 The Authors. by Ltd. https://creativecommons.org/licenses/by-nc-nd/4.0/ ) were This is an open accessPublished article under the CC BY-NC-ND license (deep). © The Authors. Published by Elsevier Elsevier Ltd. intermediate, renovation scenarios were developed (shallow, To estimate the error, obtained heat demand values This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review responsibility of the scientific committee of the International Scientific Conference https://creativecommons.org/licenses/by-nc-nd/4.0/ ) This is an open access article under the CC BY-NC-ND license ( comparedand with results from a dynamic heat demand model, previously and validated by theConference authors. ‘Environmental Selection peer-review under responsibility of the scientific committeedeveloped of the International Scientific ‘Environmental and Climate Technologies’, CONECT 2018. Selection and peer-review under responsibility of the scientific committee of the International Scientific Conference TheClimate results Technologies’, showed that when only weather and CONECT 2018. change is considered, the margin of error could be acceptable for some applications ‘Environmental and Climate CONECT (the error in annual demandTechnologies’, was lower than 20% for2018. all weather scenarios considered). However, after introducing renovation Keywords: phosphogypsum; dehydration temperature; settingon time; strength; plasticizers scenarios,dihydrate the error value increased up to 59.5% (depending thecompressive weather and renovation scenarios combination considered). Keywords: dihydrate phosphogypsum; dehydration temperature; setting time; compressive strength; The value of slope coefficient increased on average within the range of 3.8% up to plasticizers 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +371-2606-2011; fax: +371-6708-9248. Cooling.

address:author. [email protected] * E-mail Corresponding Tel.: +371-2606-2011; fax: +371-6708-9248. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. This is an open access under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 1876-6102 © 2018 Thearticle Authors. Published by Elsevier Ltd. Selection under responsibility of the scientific of the International Scientific Conference ‘Environmental and Climate This is an and openpeer-review access article under the CC BY-NC-ND licensecommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) Technologies’, CONECT 2018. Selection and peer-review under responsibility of the scientific committee of the International Scientific Conference ‘Environmental and Climate 1876-6102 © 2017 The Authors. by Elsevier Ltd. Technologies’, CONECT 2018. Published 1876-6102  2018 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the International Scientific Conference ‘Environmental and Climate Technologies’, CONECT 2018. 10.1016/j.egypro.2018.07.096

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1. Introduction In the phosphate fertilizers production process from the phosphate containing ore, a part of production waste is converted to the calcium sulfate in the reaction of apatite, phosphorite and sulfuric acid [1]. To produce 1 t of orthophosphoric acid about 3.0–4.5 t of phosphogypsum (PG) is obtained. The annual PG production reaches 280 Mt worldwide and only about 15 % of PG is used as secondary raw material, but rest is disposed in open type stacks [2]. The major mineral of PG is calcium sulfate hemihydrate and usually it is in range from 90.4–97.8 %. The PG could be contaminated with technological impurities such as orthophosphoric acid (H3PO4), sulfuric acid (H2SO4), calcium orthophosphate, calcium fluoride (CaF2), hexafluorosilicic acid (H2SiF6), phosphates and other rare element earth metals [3]. The total P2O5 content in PG traditionally is in the range from 0.28 to 1.12 % while soluble P2O5 content is in the range from 0.03–0.37 %. P2O5 is a powerful desiccant and dehydrating agent therefor it may attract water that could increase the moisture content in gypsum material lowering its properties. P2O5 is also corrosive as in reaction with water it forms phosphoric acid. To prevent such disadvantage often quicklime or slacked lime is used to neutralize acidic reaction. The soluble impurities (soluble P2O5 and F2) are converted to insoluble matters such as calcium orthophosphates of the hydroxyl apatite group (Ca3(PO4)2, etc.) and fluorides (CaF2, etc.), having little influence on the properties of binder [4]. It has been previously studied that quicklime can significantly improve the PG hydration performance by neutralizing soluble acid impurities and also shorten the setting time of binder [5]. The setting of a PG hemihydrate binder begins in 3–5 min after its tempering with water. The setting time of thermally treated PG largely depends on the raw material chemical composition, technology of treatment (thermal, milling), storage duration and presence of chemical additives. The rapid setting of thermally treated PG in numerous industrial processes is a positive factor that enables fast extraction of articles from molds and their higher turnover rate in assembly-line production. Plasticizers are often used to improve properties of thermally treated PG and to reduce water/phosphogypsum ratio (W/PG), i.e. traditionally lignosulfonate based dispersants is used in the manufacture of gypsum base products [6]. It is reported that polycarboxylic superplasticizers is used to reduce W/PG ratio significantly while the same superplasticizer has low water reduction capacity for alpha gypsum [7]. Chemical admixtures normally favor to improve technological properties of gypsum binder, such as strength, setting time, water absorption, softening coefficient, etc. Present research is focused on evaluation of gypsum binder’s technological properties obtained from dihydrate phosphogypsum treated at different temperatures. The effect of slacked lime additive and plasticizers were analysed. 2. Materials and methods Air dry PG obtained from open stacks of fertilizer production plant (AB Lifosa, Lithuania) was used. During the production PG was extracted from Kovdor apatite (Russia). The temperature of extracted PG is 62–69 °C directly after production and the typical moisture content is from 23–29 %. The pH of PG is in range from 2.2–2.9. Extracted PG is stored in open stacks where hydration and dissolution processes occur. The total amount of other components was analyzed by the complete chemical analysis according to LVS EN 196-2. The amount of P2O5 was determined according to LVS EN 196-2 using the yellow phosphor-vanadium-molybdenum complex. The chemical composition of PG is given in Table 1. The total amount of calcium sulfate dihydrate is 91.6 %. Small amount of SiO2 (4.8 %) present in the composition of PG. The total fluoride F2(T) content is 0.7, while soluble fluoride F2(s) – 0.2 %, total phosphorus pentoxide P2O5(T) content – 1.7, but soluble P2O5(s) – 0.5 respectively. Slacked lime (Natura, Poland) with grade CL 90-S according to EN 459 was used. Two types of plasticizers were used: lignosulfonate based dispersant BV 3M (Sika) and rosin resin based plasticizer Vinmix (Vincents Polyline). Both plasticizers have conformity of EN 934-2. The effect of heat treatment temperature was tested in range from 100 °C to 180 °C with 20 °C interval. Weight loss was determined for 800 g ± 50 g of samples in heating chamber up to 24 h interval. The dihydrate PG treated for 4 h at selected temperature was used for experiments. Heat treated PG was ground in planetary ball mill Retsch PM400 for 5 minutes.



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Table 1. Chemical composition of raw materials. Elements

Chemical composition, % PG

SL

CaO

37.6

95.6

SO3

54

0.1

Al2O3

0.26

-

SiO2

4.8

-

MgO

0.8

0.7

Fe2O3

0.1

-

CO2

-

F2_(T)

0.7

F2_(s)

0.2

P2O5_(T)

1.7

P2O5_(s)

0.5

0.5

-

The mixture compositions used in experiments are given in Table 2. Four mixture compositions were prepared for PG binder treated at each selected temperature. Two compositions were with W/PG ratio 0.80 – PG without additives and PG with 10 wt % of slacked lime additive. Two compositions were made with plasticizers and W/PG ratio of 0.435 and tested. Chemical admixtures were added 10 wt % of PG binder. The setting time of obtained binder was tested using Vicat apparatus. Early age (2 h) and long term (14 d) compressive strength of samples with dimension of 20ꞏ20ꞏ20 mm was tested by using universal testing system Zwick Z100 with testing speed 0.5 mm/min. Moisture content of prepared samples was determined by drying samples at 40 °C temperature until constant mass was reached. The specific gravity and total porosity was determined by using Le Chatelier flask. The mineralogical composition was determined by X-ray diffraction (XRD) (PAN analytical X’Pert PRO). Table 2. Mixture compositions of phosphogypsum binding materials. Component

Mixture composition 0Ca80

10Ca80

10V43

Heat treated phosphogypsum*

1

1

1

1

Slacked lime

-

0.1

-

-

Water

0.8

0.8

0.435

0.435

Plasticizer BV-3M

-

-

-

Plasticizer Vinmix

0.1

10B43

0.1

-

*Prepared mixture compositions with dihydrate phosphogypsum treated at 100 °C, 120 °C, 140 °C, 160 °C and 180 °C temperatures.

3. Results and discussion The weight loss of heat treated PG at different temperatures is given in Fig. 1. The heat treatment temperature has significant influence on dehydration time of PG. At dehydration temperatures 160 °C and 180 °C only 4 h is needed to reach maximal dehydration of PG and according to XRD hemihydrate gypsum was obtained. Heat treatment at lower temperatures increased dehydration time significantly. At 140 °C similar weight loss to higher temperature counterparts was observed after 24 h heat treatment. At 100 °C and 120 °C after 24 h weight loss was 22 wt % and 26 wt % comparing to the data obtained for samples treated at higher temperatures (28–29 wt %).

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304 4 30,0

Weight loss, wt%

25,0 20,0

100 °C 120 °C 140 °C 160 °C 180 °C

15,0 10,0 5,0 0,0

0

2

4

6

8

10

12 14 Time, h

16

18

20

22

24

Fig. 1. The weight loss of PG during heat treatment at different temperatures.

The mineralogical composition of PG transformation through dehydration and hydration processes is given in Fig. 2. The main mineral in dihydrate PG was synthetic calcium sulfate hydrate (CaSO4 ꞏ2H2O, ref. 33-0311). The dehydration at 180 °C for 4 h results in weight loss (28–29 wt %) of chemically bonded water and new phase – calcium sulfate hemi-hydrate (2CaSO4ꞏH2O, ref. 02-0667) was detected. For hardened samples prepared from PG treated at 180 °C (0Ca80 and 10Ca80) main mineral which was detected is calcium sulfate hydrate (ref. 72-0596) indicating reverse hydration reaction to dehydration. The addition of slacked lime in mixture composition referred to appearance of portlandite Ca(OH)2 (ref. 72-0156) in mixture composition 10Ca80.

Fig. 2. The transformation of PG mineralogical composition through dehydration and hydration processes. DH – calcium sulfate hydrate (33-0311), HH – calcium sulfate hemi-hydrate (02-0667), PL – portlandite Ca(OH)2 (ref. 72-0156).

The setting time and physical properties of obtained PG binder is given in Table 3 and Table 4. The setting time was influenced both by selected heat treatment temperature and additives which were used for preparing mix compositions. The effect of additives depended from the heat treatment temperature. Mixture design without additives (0Ca80) with PG treated at 100 °C had slow setting time with tinitial 5:30 min and tfinal 16:30 min which is associated with poorly dehydrated PG which has slow water attraction rate. PG treated at 120 and 140 °C was associated with rapid hydration process and tinitial was below 1 minute, while the tfinal was 1:40 min at 120 °C and 4:20 min at 140 °C. The accelerated setting time could be explained by partially dehydrated PG during heat treatment where remained fine calcium sulfate dihydrate powder could react as accelerator by acting as seed crystal [8]. PG treated at 160 °C and 180 °C provided similar setting time – tinitial 2:30–2:34 min and tfinal 4:40 to 4:50 min respectively which is a typical setting time of gypsum binders [9]. Slacked lime additive generally increased setting time which could be positive effect if longer working time is needed. Only for PG treated at 180 °C the setting time



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remained similar or slightly shorter (tinitial 2:10 and tfinal 4:40 min). Selected plasticizers had different effect of PG setting time. The rosin resin plasticizer acted as accelerator and reduced setting time of PG. The rosin resin based surfactant molecule structure where the polar group of a molecule sticks outward, lowers the surface tension of water and promotes hydration process. Other effect of rosin resin base plasticizer is the effect of air entraining properties therefore they also help in reducing bleeding and segregation, and improve the workability [10]. Lignosulfonate based plasticizer acted as strong setting time retarder. Initial setting time was increased from 2:23 min up to 21:00 min. Traditionally, lignosulfonate based dispersants disperse the flocculated gypsum particles through a mechanism of electrostatic repulsion resulting in a set-retarding effect [11]. Table 3. The setting time dependence of heat treatment PG temperature and admixtures. Mixture composition

Temperature of heat treatment, °C/setting time, min 100

120

140

160

180

tinitial

tfinal

tinitial

tfinal

tinitial

tfinal

tinitial

tfinal

tinitial

tfinal

0Ca80

5:30

16:30

<1

1:40

<1

4:20

2:35

4:40

2:30

4:50

10Ca80

7:00

23:20

<1

3:15

1:45

3:45

3:40

6:20

2:10

4:40

10V43

6:00

13:00

<1

1:45

<1

2:00

2:00

3:45

1:00

2:30

10B43

21:00

1:00:00

2:23

4:55

3:40

6:45

12:45

22:30

6:45

14:45

The noticeable shrinkage was observed for PG samples prepared from PG treated at temperature 100 °C (0Ca80) which could be associated with high free water content which evaporated and was also accompanied with shrinkage. The apparent density for these samples was 1406 kg/m3. High W/PG ratio 0.80 resulted in total porosity from 51 to 56 vol. % and density from 955 to 1089 kg/m3 and was little affected by heat treatment temperature and slacked lime additive. Samples with W/PG ratio 0.435 reduced free water (technological or rheological water) content and resulted lower volume of total porosity (from 36 to 48 vol. %). By increasing the heat treatment temperature of PG the total porosity decreases for samples obtained from PG. Mixtures with W/PG ratio of 0.80 have high content of free water for and it promote high moisture content in the prepared samples after 2 h of hardening (26.1 to 33.4 wt %). The moisture content slightly decreased by increase heat treatment temperature of PG. The moisture for samples (W/PG – 0.435) which were produced with plasticizers was lower comparing to high W/PG ratio counterparts – it was from 26.2 to 15.8 wt %. Lowest water content was for PG dehydrated at 180 °C. According to the data obtained in that research and with published by other authors – traditionally high free water content in gypsum binders reduce its mechanical properties [12]. Table 4. Physical properties of binders made of PG treated at different temperatures. Mixture composition 0Ca80

10Ca80

10V43

10B43

Property

Temperature of heat treatment, °C 100

120

140

160

180

Density, kg/m

1406

955

1032

1041

1024

Total porosity, vol. %

36

57

53

53

54.9

Moisture content at 2 h, wt %

-

33.0

28.3

28.9

27.9

Density, kg/m

988

1028

1086

1102

1089

Total porosity, vol. %

56

55

52

51

51.9

3

3

Moisture content at 2 h, wt %

33.4

31.7

27.0

27.2

26.1

Density, kg/m3

1207

1152

1262

1336

1359

Total porosity, vol. %

45

48

43

40

39

Moisture content at 2 h, wt %

26.2

22.1

18.7

16.5

16.0

Density, kg/m

1259

1278

1437

1416

1400

Total porosity, vol. %

43

42

35

36

37

Moisture content at 2 h, wt %

23.7

19.4

15.2

17.1

15.8

3

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The early age compressive strength for 2 h old samples is given in Fig. 3. The early age compressive strength (2 h after mixing) was affected by the setting time, admixtures and free moisture content in the samples. The early age compressive strength increased significantly when heat treatment temperature of PG was above 100 °C. The samples prepared from PG heated at temperature 100 °C showed compressive strength from 0.1–0.3 MPa while mixture composition 0Ca80 was not tested due to low strength and plastic nature at early age (hardening of paste was not occurred). The compressive strength was increased to 6 MPa by addition of slacked lime in mixture composition made of PG treated at 120 °C and 140 °C temperatures. As slacked lime increased the setting time of PG, the hydration process was slightly retarded which enabled to pour prepared fresh paste in molds avoiding the distraction of structure formation. Early age compressive strength was 2.9 MPa for 0Ca80, 5.2 MPa for 10Ca80 (120 °C) and 5.8–6.3 MPa (140 °C), respectively. The compressive strength for samples with and without slacked lime addition and made by PG treatment at 160 °C and 180 °C temperatures are quite similar – 6.3–6.8 MPa. Rosin resin based plasticizer increased early age compressive strength significantly for samples made of PG treated at 120–180 °C temperatures; compressive strength increased from 7.1 MPa (120 °C) to 15.4 MPa (180 °C) respectively. This could be associated with faster setting time comparing to other mixture compositions and modification of internal structure of the binder, also this should be investigated in details later. The lignosulfonate based dispersant retarded initial and final setting time therefore small increase of early age compressive strength (6.1 to 9.5 MPa) was observed even with low W/PG ratio. 18,0

Compressive strength, MPa

16,0

15

14

14,0

13

12,0 10,0 7

8,0 5

6,0

0,0

6

6

6

7 7

8

0,0 0,2

0,2

100

0Ca80 10Ca80

6 7

10V43 10B43

4

4,0 2,0

9

9

0,3 120

140

160

180

Dehydration temperature, °C Fig. 3. Early age (2 h) compressive strength of binder made of PG treated at different temperatures.

The compressive strength of prepared PG samples (14 days old samples) is given in Fig. 4. The significant increase of strength was observed for air dry samples. Lowest strength (from 3 to 8 MPa) was observed for samples made of PG treated at temperature 100 °C. The heat treatment temperature from 120 °C to 180 °C provided similar tendency of the compressive strength results. PG series without plasticizers provided compressive strength from 13 to 16 MPa both with slacked lime and without slacked lime additive and was not affected by the heat treatment temperature of PG. The addition of plasticizer and reduction of W/PG ratio leads to increasing of compressive strength from 18 to 29 MPa. The strength in general was higher for rosin resin and lignosulfonate based plasticizer as the W/PG ratio was the lowest.



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307 7

35 29

Compressive strength, MPa

30 25

21

23

22

20

15 13 13

15 10 5 0

13

24

20 16

15

22

14

14

18

0Ca80 10Ca80 10V43

7 8

10B43

6 3 100

120

140 160 Dehydration temperature, °C

180

Fig. 4. 14-day compressive strength of air dry binder prepared from PG treated at different temperatures.

4. Conclusions The increase of heat treatment temperature (to 160–180 °C) reduced time (to 4 h) to obtain hemihydrate phosphogypsum (PG) from dihydrate PG. The heat treatment at 120–140 °C temperature takes longer time to form hemihydrate PG therefore dihydrate particles remain in the binder which accelerates the setting time of such binder making complicate casting of fresh paste. Rosin resin and lignosulfonate base plasticizers reduced water-phosphogypsum ratio from 0.80 to 0.43, increased compressive strength and, additionally, lignosulfonate plasticizer increased initial and final setting time significantly. Early age (2 h) compressive strength for moist samples (16–33 wt %) could reach up to 15 MPa for samples with plasticizers while without chemical admixtures it was from 6 to 15 MPa. The dry sample compressive strength at the age of 14 d reached up to 29 MPa with PG treated at 180 °C and rosin resin based plasticizer (W/PG ratio of 0.425) giving a promising results considering PG as secondary raw material for binder production. Acknowledgements This work has been supported by the European Regional Development Fund within the Activity 1.1.1.2 “Post-doctoral Research Aid” of the Specific Aid Objective 1.1.1 “To increase the research and innovative capacity of scientific institutions of Latvia and the ability to attract external financing, investing in human resources and infrastructure” of the Operational Programme “Development of sustainable and effective lightweight building materials based on secondary resources” (No. 1.1.1.2/VIAA/1/16/050). References [1] [2] [3] [4] [5]

Gaiducis S, Maciulaitis R, Kaminskas A. Eco‐balance features and significance of hemihydrate phosphogypsum reprocessing into gypsum binding materials. J. Civ. Eng. Manag. 2009;15(2):205–13. Perez-Lopez R, Alvarez-Valero AM, Nieto JM. Changes in mobility of toxic elements during the production of phosphoric acid in the fertilizer industry of Huelva (SW Spain) and environmental impact of phosphogypsum wastes. J. Hazard. Mater. 2007;148(3):745–50. Gaiducis S. Mechanines aktyvacijos ir priedu poveikis ekstrakcinio pushidracio fosfogipso ir jo gaminiu savybems. Vilnus: Vilnius Gedeminas Technical University; 2010. Singh M. Effect of phosphatic and fluoride impurities of phosphogypsum on the properties of selenite plaster. Cem. Concr. Res. 2003;33(9):1363–9. Jiang G, Wu A, Wang Y, Lan W. Low cost and high efficiency utilization of hemihydrate phosphogypsum: Used as binder to prepare filling material. Constr. Build. Mater. 2018;167:263–70.

308 8 [6]

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Northey RA. The Use of Lignosulfonates as Water Reducing Agents in the Manufacture of Gypsum Wallboard. Chemical Modification, Properties and Usage of Lignin. Boston: Springer; 2002. [7] Dolak D, Dvorak K. Impact of Plasticizers on Technological Properties of Gypsum. Mater. Sci. Forum 2016;865:130–4. [8] Muller M, Fischer H, Borgardt N, Solovev S, Shlonkina S, Garkawi MS. To the Influence of Set-Controlling Additives on the Strength Development and Elongation of Calcium Sulphate Binders. [9] Dvorak D-IK, Hajkova D-II, Marcela I. Influence of grinding α -gypsum on its final property. [10] Chemical Admixtures. Available: http://www.theconcreteportal.com/admix_chem.html [11] Dawn E, Savoly A. Gypsum Wallboard Chemical Additives. GEO Specialty Chemicals 2015;1–19. [12] Gaiducis S, Zvironaite J. Mechanines aktyvacijos itaka sukietejusios kompozicines fosfogipso risamosios medziagos struktura. Chemine Technologija. Kaunas: Technologija; 2015.