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Kinetic modelling of cadmium removal from wet phosphoric acid by precipitation method
Hydrometallurgy 190 (2019) 105157
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Kinetic modelling of cadmium removal from wet phosphoric acid by precipitation method
T
⁎
Jakub Zieliński , Marta Huculak-Mączka, Maciej Kaniewski, Dominik Nieweś, Krystyna Hoffmann, Józef Hoffmann Department of Chemical Technology and Processes, Faculty of Chemistry, Wrocław University of Science and Technology, ul. M. Smoluchowskiego 25, 50-372 Wrocław, Poland
A R T I C LE I N FO
A B S T R A C T
Keywords: Kinetic modelling Wet phosphoric acid Cadmium removal Precipitation method
Phosphate fertilizers are most commonly obtained from wet phosphoric acid, which contains a majority of impurities that were present in raw materials used during the production process. It is essential to limit heavy metal contents, including cadmium, in manufactured phosphoric acid for environmental protection purposes. This work investigates kinetics of cadmium removal from wet phosphoric acid by precipitation method. Precipitating agents used in this study are: zinc ethylphenyldithiocarbamate (ZnEPDTC), sodium ethylphenyldithiocarbamate (NaEPDTC), sodium cellulose xanthate (SCX), sodium dibutyldithiocarbamate (NaDBDTC) and sodium sulfide (Na2S). For each agent, a proper cadmium reaction model is fitted, the simplified kinetic mechanism is proposed and pseudo-kinetic parameters are derived. Analysed precipitating agents were found to perform following three different mechanisms – ZnEPDTC and NaEPDTC did not react with cadmium ions in investigated conditions, SCX and NaDBDTC were decreasing the concentration of cadmium ions over time and Na2S initially decreased cadmium concentration to almost zero and then created Cd(HS)x2−x complexes.
1. Introduction
phosphoric acid. It is, however, contaminated with most of the impurities present in minerals used as substrates in production process, including the most dangerous heavy metals for biological life, such as nickel, chromium and cadmium (Gilmour, 2017). Because of its low quality, wet phosphoric acid was historically precluded from use in businesses requiring high-purity acid, such as fertilizer production. However, its low price and energy demand caused fertilizer industry to switch to wet phosphoric acid recently. Nevertheless, fully responsible and sustainable production of phosphate fertilizers from wet phosphoric acid requires developing an efficient method to remove impurities that contaminate the acid (Gilmour, 2017). Due to legislative restrictions, cadmium is one of the impurities that particularly draws researchers' attention (Cichy et al., 2014). The analysis of the available literature shows that cadmium can be removed in various ways – through extraction (Huculak-Mączka et al., 2017; Kherfan, 2011; Mahmoud and Mohsen, 2011; Mellah and Benachour, 2006; Ocio et al., 2006; Touati et al., 2009), phospho-gypsum adsorption (co-crystallization) (Balkaya and Cesur, 2008; Raii et al., 2014; Samarane et al., 2018), crystallization (Dotremont et al., 1991), adsorption and biosorption (Ahmaruzzaman and Gupta, 2011; Gupta
Phosphorus, nitrogen and potassium are three major biogenic macronutrients that are the most vital elements to ensure existence of all living organisms (Nath and Tuteja, 2016). Phosphorus concentration in soil is therefore a crucial element for plant growth and due to the lack of it in many agricultural areas it has to be supplemented with fertilizers (Kulcheski et al., 2015). These fertilizers are essential to meet nutrition needs of people worldwide. They allow for a significant increase in agricultural yields ensuring an adequate amount of food. Phosphate fertilizers are based on phosphoric acid, which is industrially produced by two main routes – the so called ‘wet route’ and ‘thermal route’ (Gilmour, 2017). In the thermal route, vapour phosphorus is combusted in controlled conditions to yield phosphoric acid. The obtained product is of high quality, but it is also very expensive because of method's large energy consumption. In the wet route, phosphorus-rich minerals are digested with sulphuric acid, forming phosphoric acid and calcium sulphate (often referred to as ‘phosphogypsum’ to indicate its origins) as a byproduct. This process does not require high energy input and therefore obtained product is relatively cheap in comparison to thermal
⁎
Corresponding author. E-mail address: jozef.hoff[email protected] (J. Zieliński).
https://doi.org/10.1016/j.hydromet.2019.105157 Received 22 March 2019; Received in revised form 26 August 2019; Accepted 29 September 2019 Available online 15 October 2019 0304-386X/ © 2019 Elsevier B.V. All rights reserved.
Hydrometallurgy 190 (2019) 105157
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with an addition of appropriate amounts of cadmium ions due to their low concentration in raw wet phosphoric acid. Removal of cadmium ions was carried out via precipitation of cadmium sulfide, using zinc ethylphenyldithiocarbamate, sodium ethylphenyldithiocarbamate, sodium cellulose xanthate, sodium dibutyldithiocarbamate and sodium sulfide as precipitation agents. All reagents were produced by POCh Gliwice. The experiments were carried out in a thermostated water bath with a shaker model 357 produced by Unipan. The precipitate was separated on hard filters and the content of cadmium ions was determined in the filtrate.
et al., 2015; Gupta and Saleh, 2013; Mahvi and Diels, 2004), membrane (Elleuch et al., 2006) and liquid membrane processes (Kislik and Eyal, 2000; Urtiaga et al., 2000), and precipitation (Abdalbake and Shino, 2004; Ennaassia et al., 2002; Ukeles et al., 1994; Zieliński et al., 2019). Only a few of above-mentioned methods have been tested in industrial practice. While sorption and membrane processes seem very perspective, they have not been tested on a large scale. They suffer from low selectivity towards cadmium removal. New materials need to be researched in order to improve them and only then pilot plants can be built. The biggest issue of the co-crystallization method is the quality of produced phospho-gypsum which is unmarketable and hard to use in other branches of industry (Lampariello, 2018). Additionally, cadmium has a 100 times better affinity for anhydrite than for gypsum, which inflicts problems with the growth of crystals and the filtration step (Cichy et al., 2014). Generally, extraction method involves pre- and post-treatment for cadmium in order for it to be extracted efficiently. It also requires large quantities of solvent to be used which is questionable from the environmental point of view. Precipitation method, on the other hand, is well established in the literature and can be easily implemented into existing plants with low costs. The obtained precipitate is rich in heavy metals and can be further processed or easily stored and the required S2− excess can be easily removed as volatile H2S (Ennaassia et al., 2002). It seems that, due to the economic and environmental reasons, the application of precipitation method has promising importance in solving cadmium problem in fertilizer industry. Equilibrium thermodynamic data of CdS precipitation with Na2S from wet phosphoric acid is available in the literature (Ennaassia et al., 2002). According to these researchers, cadmium removal efficiency decreases with the increase of temperature and acid concentration. However, it is possible to achieve 100% cadmium removal with a large excess of S2− ions and with a fairly diluted phosphoric acid. No attempts have been made to investigate the dynamic behaviour of the system. This work presents a mathematical model for cadmium removal kinetics from wet phosphoric acid by precipitation method applying various precipitating agents. Up to this day there was no data available in the literature regarding this topic.
3. Results and discussion Five experiments were carried out for various cadmium precipitating agents – zinc ethylphenyldithiocarbamate, sodium ethylphenyldithiocarbamate, sodium cellulose xanthate, sodium dibutyldithiocarbamate and sodium sulfide. The temperature was set to 20 °C for each experiment and the agents were added in the amount of 0.5 wt% in reference to the wet phosphoric acid (except sodium cellulose xanthate – 1 wt% and sodium sulfide – 0.2 wt%). Additionally, oxalic acid was added to each sample (experiment with sodium sulfide as precipitating agent being the only exception) in the amount of 0.5 wt % in reference to the wet phosphoric acid. For each experiment, liquid samples were taken after 1, 5, 10, 30, 45, and 60 min and cadmium concentration was measured. Collected results are shown in Table 2. An analogous model to Pareto distribution was then fitted to results of each experiment, applying the least squares method in order to derive the rate of cadmium reaction with the appropriate agent and a possible reaction mechanism. 3.1. Zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate For zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate used as cadmium precipitating agents there was no visible correlation between time and cadmium concentration. The performed analysis showed that the model which can be fitted best to the experimental results is constant cCd = a with the value a equal to the average cadmium concentration in time. These results are presented in Figs. 1 and 2. Therefore, for zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate the rate of cadmium removal:
2. Material and methods Samples for experiments were prepared from wet phosphoric acid obtained from Moroccan phosphorite by a local producer. The characteristics of the acid used are shown in Table 1. The colorimetric analysis using the colour reaction of the P2O5 with vanadomolybdic acid was used to determine the concentration of P2O5, which was then converted into the concentration of H3PO4. Extinction was measured at the wavelength λ = 420 nm. Cadmium concentration was determined using the colour reaction of dithizone with cadmium in the chloroform layer. The measurement was carried out at the wavelength λ = 518 nm. Before performing experiments, the wet phosphoric acid was clarified by an addition of a 2 wt% mineral‑carbon adsorbent and modified
rCd =
Value
density H3PO4 conc. Cd conc. Fe conc. Al conc. SO42− conc. Ti conc. F conc.
1.29 g/cm3 34.68 wt% 4.0 mg/kg 0.76 wt% 0.36 wt% 1.25 wt% 0.0484 wt% 2.17 wt%
(1)
3.2. Sodium cellulose xanthate and sodium dibutyldithiocarbamate Cadmium concentration decreased gradually over time when sodium cellulose xanthate and sodium dibutyldithiocarbamate were used as cadmium precipitating agents. Mathematical model fitted to define cadmium concentration is presented below: k
x cCd = offset + cMAX ⎜⎛1 − ⎛ m ⎞ ⎞⎟ t ⎠ ⎠ ⎝ ⎝
Table 1 Characteristics of wet phosphoric acid used in the study. Parameter
dcCd =0 dt
(2)
Derived model parameters are presented in Table 3, while graphs of cadmium concentration in time are shown in Figs. 3 and 4. Therefore, for sodium cellulose xanthate:
cCd = 50.8905 + 37.7012 ⎛1 − ⎛ ⎝ ⎝ ⎜
rCd =
dcCd 1 = −4.7613 ⎛ ⎞ dt ⎝t ⎠
1.5808 −0.1343⎞ ⎞ t ⎠ ⎠
(3)
0.8657
and for sodium dibutyldithiocarbamate: 2
⎟
(4)
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J. Zieliński, et al.
Table 2 Time dependence of cadmium concentration in liquid phase for various precipitating agents. Time
Zinc ethylphenyl-dithiocarbamate
Sodium ethylphenyl-dithiocarbamate⁎
Sodium cellulose xanthate
Sodium dibutyl-dithiocarbamate
Sodium sulfide
0 1 5 10 30 45 60
84.05 77.99 75.78 67.36 67.54 69.69 73.60
67.48 66.50 61.83 65.85 69.89 61.72 68.01
84.05 52.30 43.61 40.19 37.53 28.83 24.26
67.48 59.96 56.90 49.14 46.40 49.18 36.60
84.05 21.24 26.76 33.70 35.63 38.96 32.16
⁎
Results in mg Cd/kg. Table 3 Derived parameters for fitted curve modelling cadmium concentration in time using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents. Parameter
Sodium cellulose xanthate
Sodium dibutyldithiocarbamate
offset cMAX xm k
50.8905 37.7012 1.5808 −0.1343
62.3072 5.1280 0.3263 −0.3146
Fig. 1. Cadmium concentration versus time using zinc ethylphenyldithiocarbamate as precipitating agent.
Fig. 3. Cadmium concentration versus time using sodium cellulose xanthate as precipitating agent.
k1 Cd 2 + + X ⇄ CdS ↓ + Y 2 + k2
(7)
2+
where X and Y are representing precipitating agent molecule and its desulfurized ion respectively. Assuming (7) is the only reaction present in the system, the kinetic equation for cadmium removal in the form of power law can be defined as:
Fig. 2. Cadmium concentration versus time using sodium ethylphenyldithiocarbamate as precipitating agent.
cCd = 62.3072 + 5.1280 ⎛1 − ⎛ ⎝ ⎝ ⎜
rCd
0.3263 −0.3146⎞ ⎞ t ⎠ ⎠
dc 1 0.6854 = Cd = −2.2947 ⎛ ⎞ dt ⎝t ⎠
rCd = −k1 [Cd2 +]α [X]β + k2 [Y 2 +]γ
(8)
Because the precipitating agent's initial concentration was many times greater than cadmium concentration it can be assumed that it is constant:
⎟
(5)
d[X ] =0 dt (6)
(9) 2+
The only source of Y
Sodium cellulose xanthate and sodium dibutyldithiocarbamate can react with cadmium ions according to the mechanism:
[Y 2 +]
=
[Cd2 +]0 2+
where [Cd 3
−
ions is reaction (7), therefore:
[Cd2 +]
]0 is initial cadmium concentration.
(10)
Hydrometallurgy 190 (2019) 105157
J. Zieliński, et al.
Fig. 4. Cadmium concentration versus time using sodium dibutyldithiocarbamate as precipitating agent.
Fig. 5. Cadmium concentration versus time using sodium sulfide as precipitating agent.
Table 4 Derived pseudo-kinetic parameters for cadmium removal using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents.
Table 7 Derived pseudo-kinetic parameters for cadmium removal using sodium sulfide as precipitating agent.
Parameter k1′ α k2 γ
Sodium cellulose xanthate −6
5.913 • 10 3.288 0.5685 • 10−6 3.300
Sodium dibutyldithiocarbamate
Parameter
Sodium sulfide
0.6357 0.4212 1.523 0.2132
k3′ k4′ ε
57.09 33.05 0.1539
rCd = −0.6357[Cd2 +]0.4212 + 1.523([Cd2 +]0 − [Cd2 +])0.2132 Table 5 Calculated cadmium removal percentage over time from raw wet phosphoric acid containing 100 mg Cd/kg using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents. Time [min]
Sodium cellulose xanthate
Sodium dibutyldithiocarbamate
1 5 10 50 100
16,85% 42,65% 53,92% 66,46% 66,75%
2,91% 10,92% 18,13% 40,45% 44,65%
3.3. Sodium sulfide For sodium sulfide used as cadmium precipitating agent, cadmium concentration increased gradually over time. It can be assumed that an immediate reaction occurred:
Table 6 Derived parameters for fitted curve modelling cadmium concentration in time using sodium sulfide as precipitating agent. Parameter
Sodium sulfide
cMAX xm offset k
39.9302 0.2021 0.2024 0.4097
Cd 2 + + S 2 − → CdS↓
k3 CdS + H2 S ⇄Cd 2 + + 2HS − k4
(15)
Therefore, it can be assumed that the actual cadmium concentration in time t = 0 was 0 (after reaction (14) occurred). Appropriately fitted mathematical model to define cadmium concentration is presented below:
(11)
where k1′ = k1[X]β Derived pseudo-kinetic parameters corresponding to kinetic Eq. (11) for cadmium removal using sodium cellulose xanthate and sodium dibutyldithiocarbamate are presented in Table 4. Therefore, for sodium cellulose xanthate:
rCd = −5.913•10−6 [Cd2 +]3.288 + 0.5685•10−6 ([Cd2 +]0 − [Cd2 +])3.300
(14)
Cadmium sulfide precipitate was then progressively dissolving, forming a soluble complex (Ennaassia et al., 2002; Martell and Smith, 2004):
Applying Eqs. (9) and (10) to Eq. (8) gives:
rCd = −k′1 [Cd2 +]α + k2 ([Cd2 +]0 − [Cd2 +])γ
(13)
As can be seen from comparing Eqs. (12) and (13), sodium cellulose xanthate and sodium dibutyldithiocarbamate react with cadmium according to different mechanisms. Sodium cellulose xanthate was found to be a more efficient precipitating agent than sodium dibutyldithiocarbamate in investigated conditions. Calculated cadmium removal percentage over time according to Eqs. (12)–(13) from raw phosphoric acid containing 100 mg Cd/kg is presented in Table 5.
x m ⎞k ⎞ cCd = cMAX ⎜⎛1 − ⎛ ⎟ t + offset ⎝ ⎠ ⎠ ⎝
(16)
Derived model parameters are presented in Table 6, while graph of cadmium concentration in time is shown in Fig. 5. Therefore, for sodium sulfide:
(12)
and for sodium dibutyldithiocarbamate: 4
Hydrometallurgy 190 (2019) 105157
J. Zieliński, et al.
0.2021 ⎞0.4097 ⎞ cCd = 39.9302 ⎜⎛1 − ⎛ ⎟ ⎝ t + 0.2024 ⎠ ⎝ ⎠
(17)
1.4097 dcCd 1 ⎞ = 8.4968 ⎛ dt t + 0.2024 ⎝ ⎠
(18)
rCd =
in Faculty of Chemistry, Wroclaw University of Science and Technology (No. 049U/0048/19-W3/Z14, 2019-2020). References Abdalbake, M., Shino, O., 2004. Removing the cadmium, arsenic and sulfate ions from wet process phosphoric acid. Period. Polytech. Chem. Eng. 48, 63–71. Ahmaruzzaman, M., Gupta, V.K., 2011. Rice husk and its ash as low-cost adsorbents in water and wastewater treatment. Ind. Eng. Chem. Res. 50, 13589–13613. https://doi. org/10.1021/ie201477c. Asfaram, A., Ghaedi, M., Agarwal, S., Tyagi, I., Gupta, V.K., 2015. Removal of basic dye Auramine-O by ZnS:Cu nanoparticles loaded on activated carbon: Optimization of parameters using response surface methodology with central composite design. RSC Adv. 5, 18438–18450. https://doi.org/10.1039/c4ra15637d. Balkaya, N., Cesur, H., 2008. Adsorption of cadmium from aqueous solution by phosphogypsum. Chem. Eng. J. 140, 247–254. https://doi.org/10.1016/J.CEJ.2007.10. 002. Cichy, B., Jaroszek, H., Paszek, A., Tarnowska, A., 2014. Kadm w nawozach fosforowych; aspekty ekologiczne i ekonomiczne. Chemik 68, 837–842. Dotremont, C., Wilms, D., Devogelaere, D., Van Haute, A., Van Dijk, J., 1991. Recovery of cadmium by crystallization of cadmium carbonate in a fluidized-bed reactor. In: Chemistry for the Protection of the Environment. Springer US, Boston, MA, pp. 741–751. https://doi.org/10.1007/978-1-4615-3282-8_64. Elleuch, M.B.C., Amor, M. Ben, Pourcelly, G., 2006. Phosphoric acid purification by a membrane process: Electrodeionization on ion-exchange textiles. Sep. Purif. Technol. 51, 285–290. https://doi.org/10.1016/J.SEPPUR.2006.02.009. Ennaassia, E., El Kacemi, K., Kossir, A., Cote, G., 2002. Study of the removal of Cd(II) from phosphoric acid solutions by precipitation of CdS with Na2S. Hydrometallurgy 64, 101–109. https://doi.org/10.1016/S0304-386X(02)00009-9. Ghaedi, M., Hajjati, S., Mahmudi, Z., Tyagi, I., Agarwal, S., Maity, A., Gupta, V.K., 2015. Modeling of competitive ultrasonic assisted removal of the dyes - Methylene blue and Safranin-O using Fe3O4 nanoparticles. Chem. Eng. J. https://doi.org/10.1016/j.cej. 2014.12.090. Gilmour, R., 2017. Phosphoric Acid Purification, Uses, Technology, and Economics. CRC Press. Gupta, V.K., Saleh, T.A., 2013. Sorption of pollutants by porous carbon, carbon nanotubes and fullerene- an overview. Environ. Sci. Pollut. Res. https://doi.org/10.1007/ s11356-013-1524-1. Gupta, V.K., Nayak, A., Agarwal, S., Tyagi, I., 2014. Potential of activated carbon from waste rubber tire for the adsorption of phenolics: effect of pre-treatment conditions. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2013.11.067. Gupta, V.K., Nayak, A., Agarwal, S., 2015. Bioadsorbents for remediation of heavy metals: current status and their future prospects. Environ. Eng. Res. 20, 1–018. https://doi. org/10.4491/eer.2015.018. Huculak-Mączka, M., Nieweś, D., Kaniewski, M., Hoffmann, J., Hoffmann, K., 2017. Opis matematyczny oczyszczania ekstrakcyjnego kwasu fosforowego z użyciem eteru diizopropylowego. Proc. ECOpole 11, 497–505. https://doi.org/10.2429/proc.2017. 11(2)054. Kherfan, S., 2011. Extraction of cadmium from phosphoric acid by trioctylphosphine oxide/kerosene solvent using factorial design. Period. Polytech. Chem. Eng. 55, 45. https://doi.org/10.3311/pp.ch.2011-2.01. Kislik, V., Eyal, A., 2000. Aqueous hybrid liquid membrane process for metal separation: Part II. Selectivity of metals separation from wet-process phosphoric acid. J. Membr. Sci. 169, 133–146. https://doi.org/10.1016/S0376-7388(99)00332-4. Kulcheski, F.R., Côrrea, R., Gomes, I.A., de Lima, J.C., Margis, R., 2015. NPK macronutrients and microRNA homeostasis. Front. Plant Sci. 6, 451. https://doi.org/10. 3389/fpls.2015.00451. Lampariello, J., 2018. Heavy metals removal. World Fertil. 9, 75–81. Mahmoud, M.H.H., Mohsen, Q., 2011. Enhanced solvent extraction of cadmium and iron from phosphoric acid in chloride media. Physicochem. Probl. Miner. Process. 47, 27–40. Mahvi, A.H., Diels, L., 2004. Biological removal of cadmium by Alcaligenes eutrophus CH34. Int. J. Environ. Sci. Technol. 1, 199–204. https://doi.org/10.1007/ BF03325833. Martell, A.E., Smith, R.M., 2004. NIST Critically Selected Stability Constants of Metal Complexes Database. Mellah, A., Benachour, D., 2006. The solvent extraction of zinc and cadmium from phosphoric acid solution by di-2-ethyl hexyl phosphoric acid in kerosene diluent. Chem. Eng. Process. Process Intensif. 45, 684–690. https://doi.org/10.1016/j.cep. 2006.02.004. Mittal, A., Mittal, J., Malviya, A., Gupta, V.K., 2010. Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2010.01.007. Mohammadi, N., Khani, H., Gupta, V.K., Amereh, E., Agarwal, S., 2011. Adsorption process of methyl orange dye onto mesoporous carbon material-kinetic and thermodynamic studies. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2011.06. 067. Nath, M., Tuteja, N., 2016. NPKS uptake, sensing, and signaling and miRNAs in plant nutrient stress. Protoplasma 253, 767–786. https://doi.org/10.1007/s00709-0150845-y. Ocio, A., Mijangos, F., Elizalde, M., 2006. Copper and cadmium extraction from highly concentrated phosphoric acid solutions using calcium alginate gels enclosing bis (2,4,4-trimethylpentyl)thiophosphinic acid. J. Chem. Technol. Biotechnol. 81, 1409–1418. https://doi.org/10.1002/jctb.1578.
As stated before, the kinetic modelling can be applied only to Eq. (15). The kinetic equation for cadmium removal in the form of power law is presented below:
rCd = k3 [H2 S]δ − k 4 [Cd2 +]ε [HS −]ζ
(19)
Sodium sulfide dissociates in water:
Na2 S → 2Na+ + S 2 −
(20)
Sulfide ion then forms a series of equilibriums:
S 2−
+ H+ ⇄ HS −
HS −
+
H+
(21) (22)
⇄ H2 S
Because the initial concentration of sodium sulfide (and therefore also the sulfide ion) is many times greater than cadmium concentration, it can be assumed that it is constant as well as its all derivatives (assuming that equilibrium conditions for H2S are met immediately):
d[H2 S ] d[HS −] d[S 2 −] = = =0 dt dt dt
(23)
Applying Eqs. (23) to (19) gives:
rCd = k′3 − k′4 [Cd2 +]ε
(24) δ
− ζ.
where k3′ = k3[H2S] and k4′ = k4[HS ] Derived pseudo-kinetic parameters corresponding to kinetic Eq. (24) for cadmium removal with the use of sodium sulfide are presented in Table 7. Therefore, for sodium sulfide:
rCd = 57.09 − 33.05[Cd2 +]0.1539
(25)
4. Conclusions The performed analysis shows that ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate do not react with cadmium in investigated conditions. Sodium cellulose xanthate and sodium dibutyldithiocarbamate gradually lower cadmium concentration in the liquid phase over time but observed reactions occur following different reaction mechanisms. Excess organic compounds remaining in the acid can be a subject to removal by adsorption or photocatalytic degradation (Asfaram et al., 2015; Ghaedi et al., 2015; Gupta et al., 2014; Mittal et al., 2010; Mohammadi et al., 2011; Saravanan et al., 2016). Sodium sulfide can be regarded as an efficient precipitating agent for cadmium ions removal. Immediately after applying it to the system, cadmium concentration decreases to values near zero and then increases due to cadmium sulfide precipitate dissolving. Therefore, in order to achieve a high cadmium removal (ηCd) value, cadmium sulfide precipitate has to be filtered out as quickly as possible. Additionally, a distinct smell of hydrogen sulfide was present during the whole experiment, which makes sodium sulfide a questionable precipitating agent due to the environmental and safety reasons. Declaration of Competing Interest None. Acknowledgement The work was supported by the Ministry of Science and Higher Education of Poland within a frame of statutory activity grant realized 5
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of a continuous extraction-stripping process. Hydrometallurgy. https://doi.org/10. 1016/j.hydromet.2008.05.012. Ukeles, S.D., Ben-Yoseph, E., Finkelstein, N.P., 1994. Cadmium removal from phosphoric acid — Israeli experience. In: Hydrometallurgy. Springer Netherlands, Dordrecht, pp. 683–699. https://doi.org/10.1007/978-94-011-1214-7_45. Urtiaga, A.M., Alonso, A., Ortiz, I., Daoud, J.A., El-Reefy, S.A., Pérez de Ortiz, S., Gallego, T., 2000. Comparison of liquid membrane processes for the removal of cadmium from wet phosphoric acid. J. Membr. Sci. 164, 229–240. https://doi.org/10.1016/S03767388(99)00197-0. Zieliński, J., Huculak-Mączka, M., Porwoł, M., Kaniewski, M., Nieweś, D., Hoffmann, K., 2019. Badania oczyszczania surowego ekstrakcyjnego kwasu fosforowego. Przemysł 98, 1000–1004. https://doi.org/10.15199/62.2019.7.XX.
Raii, M., Minh, D.P., Sanz, F.J.E., Nzihou, A., 2014. Lead and cadmium removal from aqueous solution using an industrial gypsum by-product. Procedia Eng. 83, 415–422. https://doi.org/10.1016/J.PROENG.2014.09.050. Samarane, K., Boulif, R., Dhiba, D., Bouhaouss, A., 2018. Improvements and intesification of industrial co-crystallization process for cadmium removal from wet phosphoric acid. Int. J. Eng. Sci. Res. Technol. 7, 152–163. https://doi.org/10.5281/zenodo. 1476369. Saravanan, R., Sacari, E., Gracia, F., Khan, M.M., Mosquera, E., Gupta, V.K., 2016. Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes. J. Mol. Liq. https://doi.org/10.1016/j.molliq.2016.06.074. Touati, M., Benna-Zayani, M., Kbir-Ariguib, N., Trabelsi-Ayadi, M., Buch, A., Grossiord, J.L., Pareau, D., Stambouli, M., 2009. Extraction of cadmium (II) from phosphoric acid media using the di(2-ethylhexyl)dithiophosphoric acid (D2EHDTPA): feasibility
6
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Kinetic modelling of cadmium removal from wet phosphoric acid by precipitation method
T
⁎
Jakub Zieliński , Marta Huculak-Mączka, Maciej Kaniewski, Dominik Nieweś, Krystyna Hoffmann, Józef Hoffmann Department of Chemical Technology and Processes, Faculty of Chemistry, Wrocław University of Science and Technology, ul. M. Smoluchowskiego 25, 50-372 Wrocław, Poland
A R T I C LE I N FO
A B S T R A C T
Keywords: Kinetic modelling Wet phosphoric acid Cadmium removal Precipitation method
Phosphate fertilizers are most commonly obtained from wet phosphoric acid, which contains a majority of impurities that were present in raw materials used during the production process. It is essential to limit heavy metal contents, including cadmium, in manufactured phosphoric acid for environmental protection purposes. This work investigates kinetics of cadmium removal from wet phosphoric acid by precipitation method. Precipitating agents used in this study are: zinc ethylphenyldithiocarbamate (ZnEPDTC), sodium ethylphenyldithiocarbamate (NaEPDTC), sodium cellulose xanthate (SCX), sodium dibutyldithiocarbamate (NaDBDTC) and sodium sulfide (Na2S). For each agent, a proper cadmium reaction model is fitted, the simplified kinetic mechanism is proposed and pseudo-kinetic parameters are derived. Analysed precipitating agents were found to perform following three different mechanisms – ZnEPDTC and NaEPDTC did not react with cadmium ions in investigated conditions, SCX and NaDBDTC were decreasing the concentration of cadmium ions over time and Na2S initially decreased cadmium concentration to almost zero and then created Cd(HS)x2−x complexes.
1. Introduction
phosphoric acid. It is, however, contaminated with most of the impurities present in minerals used as substrates in production process, including the most dangerous heavy metals for biological life, such as nickel, chromium and cadmium (Gilmour, 2017). Because of its low quality, wet phosphoric acid was historically precluded from use in businesses requiring high-purity acid, such as fertilizer production. However, its low price and energy demand caused fertilizer industry to switch to wet phosphoric acid recently. Nevertheless, fully responsible and sustainable production of phosphate fertilizers from wet phosphoric acid requires developing an efficient method to remove impurities that contaminate the acid (Gilmour, 2017). Due to legislative restrictions, cadmium is one of the impurities that particularly draws researchers' attention (Cichy et al., 2014). The analysis of the available literature shows that cadmium can be removed in various ways – through extraction (Huculak-Mączka et al., 2017; Kherfan, 2011; Mahmoud and Mohsen, 2011; Mellah and Benachour, 2006; Ocio et al., 2006; Touati et al., 2009), phospho-gypsum adsorption (co-crystallization) (Balkaya and Cesur, 2008; Raii et al., 2014; Samarane et al., 2018), crystallization (Dotremont et al., 1991), adsorption and biosorption (Ahmaruzzaman and Gupta, 2011; Gupta
Phosphorus, nitrogen and potassium are three major biogenic macronutrients that are the most vital elements to ensure existence of all living organisms (Nath and Tuteja, 2016). Phosphorus concentration in soil is therefore a crucial element for plant growth and due to the lack of it in many agricultural areas it has to be supplemented with fertilizers (Kulcheski et al., 2015). These fertilizers are essential to meet nutrition needs of people worldwide. They allow for a significant increase in agricultural yields ensuring an adequate amount of food. Phosphate fertilizers are based on phosphoric acid, which is industrially produced by two main routes – the so called ‘wet route’ and ‘thermal route’ (Gilmour, 2017). In the thermal route, vapour phosphorus is combusted in controlled conditions to yield phosphoric acid. The obtained product is of high quality, but it is also very expensive because of method's large energy consumption. In the wet route, phosphorus-rich minerals are digested with sulphuric acid, forming phosphoric acid and calcium sulphate (often referred to as ‘phosphogypsum’ to indicate its origins) as a byproduct. This process does not require high energy input and therefore obtained product is relatively cheap in comparison to thermal
⁎
Corresponding author. E-mail address: jozef.hoff[email protected] (J. Zieliński).
https://doi.org/10.1016/j.hydromet.2019.105157 Received 22 March 2019; Received in revised form 26 August 2019; Accepted 29 September 2019 Available online 15 October 2019 0304-386X/ © 2019 Elsevier B.V. All rights reserved.
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with an addition of appropriate amounts of cadmium ions due to their low concentration in raw wet phosphoric acid. Removal of cadmium ions was carried out via precipitation of cadmium sulfide, using zinc ethylphenyldithiocarbamate, sodium ethylphenyldithiocarbamate, sodium cellulose xanthate, sodium dibutyldithiocarbamate and sodium sulfide as precipitation agents. All reagents were produced by POCh Gliwice. The experiments were carried out in a thermostated water bath with a shaker model 357 produced by Unipan. The precipitate was separated on hard filters and the content of cadmium ions was determined in the filtrate.
et al., 2015; Gupta and Saleh, 2013; Mahvi and Diels, 2004), membrane (Elleuch et al., 2006) and liquid membrane processes (Kislik and Eyal, 2000; Urtiaga et al., 2000), and precipitation (Abdalbake and Shino, 2004; Ennaassia et al., 2002; Ukeles et al., 1994; Zieliński et al., 2019). Only a few of above-mentioned methods have been tested in industrial practice. While sorption and membrane processes seem very perspective, they have not been tested on a large scale. They suffer from low selectivity towards cadmium removal. New materials need to be researched in order to improve them and only then pilot plants can be built. The biggest issue of the co-crystallization method is the quality of produced phospho-gypsum which is unmarketable and hard to use in other branches of industry (Lampariello, 2018). Additionally, cadmium has a 100 times better affinity for anhydrite than for gypsum, which inflicts problems with the growth of crystals and the filtration step (Cichy et al., 2014). Generally, extraction method involves pre- and post-treatment for cadmium in order for it to be extracted efficiently. It also requires large quantities of solvent to be used which is questionable from the environmental point of view. Precipitation method, on the other hand, is well established in the literature and can be easily implemented into existing plants with low costs. The obtained precipitate is rich in heavy metals and can be further processed or easily stored and the required S2− excess can be easily removed as volatile H2S (Ennaassia et al., 2002). It seems that, due to the economic and environmental reasons, the application of precipitation method has promising importance in solving cadmium problem in fertilizer industry. Equilibrium thermodynamic data of CdS precipitation with Na2S from wet phosphoric acid is available in the literature (Ennaassia et al., 2002). According to these researchers, cadmium removal efficiency decreases with the increase of temperature and acid concentration. However, it is possible to achieve 100% cadmium removal with a large excess of S2− ions and with a fairly diluted phosphoric acid. No attempts have been made to investigate the dynamic behaviour of the system. This work presents a mathematical model for cadmium removal kinetics from wet phosphoric acid by precipitation method applying various precipitating agents. Up to this day there was no data available in the literature regarding this topic.
3. Results and discussion Five experiments were carried out for various cadmium precipitating agents – zinc ethylphenyldithiocarbamate, sodium ethylphenyldithiocarbamate, sodium cellulose xanthate, sodium dibutyldithiocarbamate and sodium sulfide. The temperature was set to 20 °C for each experiment and the agents were added in the amount of 0.5 wt% in reference to the wet phosphoric acid (except sodium cellulose xanthate – 1 wt% and sodium sulfide – 0.2 wt%). Additionally, oxalic acid was added to each sample (experiment with sodium sulfide as precipitating agent being the only exception) in the amount of 0.5 wt % in reference to the wet phosphoric acid. For each experiment, liquid samples were taken after 1, 5, 10, 30, 45, and 60 min and cadmium concentration was measured. Collected results are shown in Table 2. An analogous model to Pareto distribution was then fitted to results of each experiment, applying the least squares method in order to derive the rate of cadmium reaction with the appropriate agent and a possible reaction mechanism. 3.1. Zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate For zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate used as cadmium precipitating agents there was no visible correlation between time and cadmium concentration. The performed analysis showed that the model which can be fitted best to the experimental results is constant cCd = a with the value a equal to the average cadmium concentration in time. These results are presented in Figs. 1 and 2. Therefore, for zinc ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate the rate of cadmium removal:
2. Material and methods Samples for experiments were prepared from wet phosphoric acid obtained from Moroccan phosphorite by a local producer. The characteristics of the acid used are shown in Table 1. The colorimetric analysis using the colour reaction of the P2O5 with vanadomolybdic acid was used to determine the concentration of P2O5, which was then converted into the concentration of H3PO4. Extinction was measured at the wavelength λ = 420 nm. Cadmium concentration was determined using the colour reaction of dithizone with cadmium in the chloroform layer. The measurement was carried out at the wavelength λ = 518 nm. Before performing experiments, the wet phosphoric acid was clarified by an addition of a 2 wt% mineral‑carbon adsorbent and modified
rCd =
Value
density H3PO4 conc. Cd conc. Fe conc. Al conc. SO42− conc. Ti conc. F conc.
1.29 g/cm3 34.68 wt% 4.0 mg/kg 0.76 wt% 0.36 wt% 1.25 wt% 0.0484 wt% 2.17 wt%
(1)
3.2. Sodium cellulose xanthate and sodium dibutyldithiocarbamate Cadmium concentration decreased gradually over time when sodium cellulose xanthate and sodium dibutyldithiocarbamate were used as cadmium precipitating agents. Mathematical model fitted to define cadmium concentration is presented below: k
x cCd = offset + cMAX ⎜⎛1 − ⎛ m ⎞ ⎞⎟ t ⎠ ⎠ ⎝ ⎝
Table 1 Characteristics of wet phosphoric acid used in the study. Parameter
dcCd =0 dt
(2)
Derived model parameters are presented in Table 3, while graphs of cadmium concentration in time are shown in Figs. 3 and 4. Therefore, for sodium cellulose xanthate:
cCd = 50.8905 + 37.7012 ⎛1 − ⎛ ⎝ ⎝ ⎜
rCd =
dcCd 1 = −4.7613 ⎛ ⎞ dt ⎝t ⎠
1.5808 −0.1343⎞ ⎞ t ⎠ ⎠
(3)
0.8657
and for sodium dibutyldithiocarbamate: 2
⎟
(4)
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Table 2 Time dependence of cadmium concentration in liquid phase for various precipitating agents. Time
Zinc ethylphenyl-dithiocarbamate
Sodium ethylphenyl-dithiocarbamate⁎
Sodium cellulose xanthate
Sodium dibutyl-dithiocarbamate
Sodium sulfide
0 1 5 10 30 45 60
84.05 77.99 75.78 67.36 67.54 69.69 73.60
67.48 66.50 61.83 65.85 69.89 61.72 68.01
84.05 52.30 43.61 40.19 37.53 28.83 24.26
67.48 59.96 56.90 49.14 46.40 49.18 36.60
84.05 21.24 26.76 33.70 35.63 38.96 32.16
⁎
Results in mg Cd/kg. Table 3 Derived parameters for fitted curve modelling cadmium concentration in time using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents. Parameter
Sodium cellulose xanthate
Sodium dibutyldithiocarbamate
offset cMAX xm k
50.8905 37.7012 1.5808 −0.1343
62.3072 5.1280 0.3263 −0.3146
Fig. 1. Cadmium concentration versus time using zinc ethylphenyldithiocarbamate as precipitating agent.
Fig. 3. Cadmium concentration versus time using sodium cellulose xanthate as precipitating agent.
k1 Cd 2 + + X ⇄ CdS ↓ + Y 2 + k2
(7)
2+
where X and Y are representing precipitating agent molecule and its desulfurized ion respectively. Assuming (7) is the only reaction present in the system, the kinetic equation for cadmium removal in the form of power law can be defined as:
Fig. 2. Cadmium concentration versus time using sodium ethylphenyldithiocarbamate as precipitating agent.
cCd = 62.3072 + 5.1280 ⎛1 − ⎛ ⎝ ⎝ ⎜
rCd
0.3263 −0.3146⎞ ⎞ t ⎠ ⎠
dc 1 0.6854 = Cd = −2.2947 ⎛ ⎞ dt ⎝t ⎠
rCd = −k1 [Cd2 +]α [X]β + k2 [Y 2 +]γ
(8)
Because the precipitating agent's initial concentration was many times greater than cadmium concentration it can be assumed that it is constant:
⎟
(5)
d[X ] =0 dt (6)
(9) 2+
The only source of Y
Sodium cellulose xanthate and sodium dibutyldithiocarbamate can react with cadmium ions according to the mechanism:
[Y 2 +]
=
[Cd2 +]0 2+
where [Cd 3
−
ions is reaction (7), therefore:
[Cd2 +]
]0 is initial cadmium concentration.
(10)
Hydrometallurgy 190 (2019) 105157
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Fig. 4. Cadmium concentration versus time using sodium dibutyldithiocarbamate as precipitating agent.
Fig. 5. Cadmium concentration versus time using sodium sulfide as precipitating agent.
Table 4 Derived pseudo-kinetic parameters for cadmium removal using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents.
Table 7 Derived pseudo-kinetic parameters for cadmium removal using sodium sulfide as precipitating agent.
Parameter k1′ α k2 γ
Sodium cellulose xanthate −6
5.913 • 10 3.288 0.5685 • 10−6 3.300
Sodium dibutyldithiocarbamate
Parameter
Sodium sulfide
0.6357 0.4212 1.523 0.2132
k3′ k4′ ε
57.09 33.05 0.1539
rCd = −0.6357[Cd2 +]0.4212 + 1.523([Cd2 +]0 − [Cd2 +])0.2132 Table 5 Calculated cadmium removal percentage over time from raw wet phosphoric acid containing 100 mg Cd/kg using sodium cellulose xanthate and sodium dibutyldithiocarbamate as precipitating agents. Time [min]
Sodium cellulose xanthate
Sodium dibutyldithiocarbamate
1 5 10 50 100
16,85% 42,65% 53,92% 66,46% 66,75%
2,91% 10,92% 18,13% 40,45% 44,65%
3.3. Sodium sulfide For sodium sulfide used as cadmium precipitating agent, cadmium concentration increased gradually over time. It can be assumed that an immediate reaction occurred:
Table 6 Derived parameters for fitted curve modelling cadmium concentration in time using sodium sulfide as precipitating agent. Parameter
Sodium sulfide
cMAX xm offset k
39.9302 0.2021 0.2024 0.4097
Cd 2 + + S 2 − → CdS↓
k3 CdS + H2 S ⇄Cd 2 + + 2HS − k4
(15)
Therefore, it can be assumed that the actual cadmium concentration in time t = 0 was 0 (after reaction (14) occurred). Appropriately fitted mathematical model to define cadmium concentration is presented below:
(11)
where k1′ = k1[X]β Derived pseudo-kinetic parameters corresponding to kinetic Eq. (11) for cadmium removal using sodium cellulose xanthate and sodium dibutyldithiocarbamate are presented in Table 4. Therefore, for sodium cellulose xanthate:
rCd = −5.913•10−6 [Cd2 +]3.288 + 0.5685•10−6 ([Cd2 +]0 − [Cd2 +])3.300
(14)
Cadmium sulfide precipitate was then progressively dissolving, forming a soluble complex (Ennaassia et al., 2002; Martell and Smith, 2004):
Applying Eqs. (9) and (10) to Eq. (8) gives:
rCd = −k′1 [Cd2 +]α + k2 ([Cd2 +]0 − [Cd2 +])γ
(13)
As can be seen from comparing Eqs. (12) and (13), sodium cellulose xanthate and sodium dibutyldithiocarbamate react with cadmium according to different mechanisms. Sodium cellulose xanthate was found to be a more efficient precipitating agent than sodium dibutyldithiocarbamate in investigated conditions. Calculated cadmium removal percentage over time according to Eqs. (12)–(13) from raw phosphoric acid containing 100 mg Cd/kg is presented in Table 5.
x m ⎞k ⎞ cCd = cMAX ⎜⎛1 − ⎛ ⎟ t + offset ⎝ ⎠ ⎠ ⎝
(16)
Derived model parameters are presented in Table 6, while graph of cadmium concentration in time is shown in Fig. 5. Therefore, for sodium sulfide:
(12)
and for sodium dibutyldithiocarbamate: 4
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0.2021 ⎞0.4097 ⎞ cCd = 39.9302 ⎜⎛1 − ⎛ ⎟ ⎝ t + 0.2024 ⎠ ⎝ ⎠
(17)
1.4097 dcCd 1 ⎞ = 8.4968 ⎛ dt t + 0.2024 ⎝ ⎠
(18)
rCd =
in Faculty of Chemistry, Wroclaw University of Science and Technology (No. 049U/0048/19-W3/Z14, 2019-2020). References Abdalbake, M., Shino, O., 2004. Removing the cadmium, arsenic and sulfate ions from wet process phosphoric acid. Period. Polytech. Chem. Eng. 48, 63–71. Ahmaruzzaman, M., Gupta, V.K., 2011. Rice husk and its ash as low-cost adsorbents in water and wastewater treatment. Ind. Eng. Chem. Res. 50, 13589–13613. https://doi. org/10.1021/ie201477c. Asfaram, A., Ghaedi, M., Agarwal, S., Tyagi, I., Gupta, V.K., 2015. Removal of basic dye Auramine-O by ZnS:Cu nanoparticles loaded on activated carbon: Optimization of parameters using response surface methodology with central composite design. RSC Adv. 5, 18438–18450. https://doi.org/10.1039/c4ra15637d. Balkaya, N., Cesur, H., 2008. Adsorption of cadmium from aqueous solution by phosphogypsum. Chem. Eng. J. 140, 247–254. https://doi.org/10.1016/J.CEJ.2007.10. 002. Cichy, B., Jaroszek, H., Paszek, A., Tarnowska, A., 2014. Kadm w nawozach fosforowych; aspekty ekologiczne i ekonomiczne. Chemik 68, 837–842. Dotremont, C., Wilms, D., Devogelaere, D., Van Haute, A., Van Dijk, J., 1991. Recovery of cadmium by crystallization of cadmium carbonate in a fluidized-bed reactor. In: Chemistry for the Protection of the Environment. Springer US, Boston, MA, pp. 741–751. https://doi.org/10.1007/978-1-4615-3282-8_64. Elleuch, M.B.C., Amor, M. Ben, Pourcelly, G., 2006. Phosphoric acid purification by a membrane process: Electrodeionization on ion-exchange textiles. Sep. Purif. Technol. 51, 285–290. https://doi.org/10.1016/J.SEPPUR.2006.02.009. Ennaassia, E., El Kacemi, K., Kossir, A., Cote, G., 2002. Study of the removal of Cd(II) from phosphoric acid solutions by precipitation of CdS with Na2S. Hydrometallurgy 64, 101–109. https://doi.org/10.1016/S0304-386X(02)00009-9. Ghaedi, M., Hajjati, S., Mahmudi, Z., Tyagi, I., Agarwal, S., Maity, A., Gupta, V.K., 2015. Modeling of competitive ultrasonic assisted removal of the dyes - Methylene blue and Safranin-O using Fe3O4 nanoparticles. Chem. Eng. J. https://doi.org/10.1016/j.cej. 2014.12.090. Gilmour, R., 2017. Phosphoric Acid Purification, Uses, Technology, and Economics. CRC Press. Gupta, V.K., Saleh, T.A., 2013. Sorption of pollutants by porous carbon, carbon nanotubes and fullerene- an overview. Environ. Sci. Pollut. Res. https://doi.org/10.1007/ s11356-013-1524-1. Gupta, V.K., Nayak, A., Agarwal, S., Tyagi, I., 2014. Potential of activated carbon from waste rubber tire for the adsorption of phenolics: effect of pre-treatment conditions. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2013.11.067. Gupta, V.K., Nayak, A., Agarwal, S., 2015. Bioadsorbents for remediation of heavy metals: current status and their future prospects. Environ. Eng. Res. 20, 1–018. https://doi. org/10.4491/eer.2015.018. Huculak-Mączka, M., Nieweś, D., Kaniewski, M., Hoffmann, J., Hoffmann, K., 2017. Opis matematyczny oczyszczania ekstrakcyjnego kwasu fosforowego z użyciem eteru diizopropylowego. Proc. ECOpole 11, 497–505. https://doi.org/10.2429/proc.2017. 11(2)054. Kherfan, S., 2011. Extraction of cadmium from phosphoric acid by trioctylphosphine oxide/kerosene solvent using factorial design. Period. Polytech. Chem. Eng. 55, 45. https://doi.org/10.3311/pp.ch.2011-2.01. Kislik, V., Eyal, A., 2000. Aqueous hybrid liquid membrane process for metal separation: Part II. Selectivity of metals separation from wet-process phosphoric acid. J. Membr. Sci. 169, 133–146. https://doi.org/10.1016/S0376-7388(99)00332-4. Kulcheski, F.R., Côrrea, R., Gomes, I.A., de Lima, J.C., Margis, R., 2015. NPK macronutrients and microRNA homeostasis. Front. Plant Sci. 6, 451. https://doi.org/10. 3389/fpls.2015.00451. Lampariello, J., 2018. Heavy metals removal. World Fertil. 9, 75–81. Mahmoud, M.H.H., Mohsen, Q., 2011. Enhanced solvent extraction of cadmium and iron from phosphoric acid in chloride media. Physicochem. Probl. Miner. Process. 47, 27–40. Mahvi, A.H., Diels, L., 2004. Biological removal of cadmium by Alcaligenes eutrophus CH34. Int. J. Environ. Sci. Technol. 1, 199–204. https://doi.org/10.1007/ BF03325833. Martell, A.E., Smith, R.M., 2004. NIST Critically Selected Stability Constants of Metal Complexes Database. Mellah, A., Benachour, D., 2006. The solvent extraction of zinc and cadmium from phosphoric acid solution by di-2-ethyl hexyl phosphoric acid in kerosene diluent. Chem. Eng. Process. Process Intensif. 45, 684–690. https://doi.org/10.1016/j.cep. 2006.02.004. Mittal, A., Mittal, J., Malviya, A., Gupta, V.K., 2010. Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2010.01.007. Mohammadi, N., Khani, H., Gupta, V.K., Amereh, E., Agarwal, S., 2011. Adsorption process of methyl orange dye onto mesoporous carbon material-kinetic and thermodynamic studies. J. Colloid Interface Sci. https://doi.org/10.1016/j.jcis.2011.06. 067. Nath, M., Tuteja, N., 2016. NPKS uptake, sensing, and signaling and miRNAs in plant nutrient stress. Protoplasma 253, 767–786. https://doi.org/10.1007/s00709-0150845-y. Ocio, A., Mijangos, F., Elizalde, M., 2006. Copper and cadmium extraction from highly concentrated phosphoric acid solutions using calcium alginate gels enclosing bis (2,4,4-trimethylpentyl)thiophosphinic acid. J. Chem. Technol. Biotechnol. 81, 1409–1418. https://doi.org/10.1002/jctb.1578.
As stated before, the kinetic modelling can be applied only to Eq. (15). The kinetic equation for cadmium removal in the form of power law is presented below:
rCd = k3 [H2 S]δ − k 4 [Cd2 +]ε [HS −]ζ
(19)
Sodium sulfide dissociates in water:
Na2 S → 2Na+ + S 2 −
(20)
Sulfide ion then forms a series of equilibriums:
S 2−
+ H+ ⇄ HS −
HS −
+
H+
(21) (22)
⇄ H2 S
Because the initial concentration of sodium sulfide (and therefore also the sulfide ion) is many times greater than cadmium concentration, it can be assumed that it is constant as well as its all derivatives (assuming that equilibrium conditions for H2S are met immediately):
d[H2 S ] d[HS −] d[S 2 −] = = =0 dt dt dt
(23)
Applying Eqs. (23) to (19) gives:
rCd = k′3 − k′4 [Cd2 +]ε
(24) δ
− ζ.
where k3′ = k3[H2S] and k4′ = k4[HS ] Derived pseudo-kinetic parameters corresponding to kinetic Eq. (24) for cadmium removal with the use of sodium sulfide are presented in Table 7. Therefore, for sodium sulfide:
rCd = 57.09 − 33.05[Cd2 +]0.1539
(25)
4. Conclusions The performed analysis shows that ethylphenyldithiocarbamate and sodium ethylphenyldithiocarbamate do not react with cadmium in investigated conditions. Sodium cellulose xanthate and sodium dibutyldithiocarbamate gradually lower cadmium concentration in the liquid phase over time but observed reactions occur following different reaction mechanisms. Excess organic compounds remaining in the acid can be a subject to removal by adsorption or photocatalytic degradation (Asfaram et al., 2015; Ghaedi et al., 2015; Gupta et al., 2014; Mittal et al., 2010; Mohammadi et al., 2011; Saravanan et al., 2016). Sodium sulfide can be regarded as an efficient precipitating agent for cadmium ions removal. Immediately after applying it to the system, cadmium concentration decreases to values near zero and then increases due to cadmium sulfide precipitate dissolving. Therefore, in order to achieve a high cadmium removal (ηCd) value, cadmium sulfide precipitate has to be filtered out as quickly as possible. Additionally, a distinct smell of hydrogen sulfide was present during the whole experiment, which makes sodium sulfide a questionable precipitating agent due to the environmental and safety reasons. Declaration of Competing Interest None. Acknowledgement The work was supported by the Ministry of Science and Higher Education of Poland within a frame of statutory activity grant realized 5
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of a continuous extraction-stripping process. Hydrometallurgy. https://doi.org/10. 1016/j.hydromet.2008.05.012. Ukeles, S.D., Ben-Yoseph, E., Finkelstein, N.P., 1994. Cadmium removal from phosphoric acid — Israeli experience. In: Hydrometallurgy. Springer Netherlands, Dordrecht, pp. 683–699. https://doi.org/10.1007/978-94-011-1214-7_45. Urtiaga, A.M., Alonso, A., Ortiz, I., Daoud, J.A., El-Reefy, S.A., Pérez de Ortiz, S., Gallego, T., 2000. Comparison of liquid membrane processes for the removal of cadmium from wet phosphoric acid. J. Membr. Sci. 164, 229–240. https://doi.org/10.1016/S03767388(99)00197-0. Zieliński, J., Huculak-Mączka, M., Porwoł, M., Kaniewski, M., Nieweś, D., Hoffmann, K., 2019. Badania oczyszczania surowego ekstrakcyjnego kwasu fosforowego. Przemysł 98, 1000–1004. https://doi.org/10.15199/62.2019.7.XX.
Raii, M., Minh, D.P., Sanz, F.J.E., Nzihou, A., 2014. Lead and cadmium removal from aqueous solution using an industrial gypsum by-product. Procedia Eng. 83, 415–422. https://doi.org/10.1016/J.PROENG.2014.09.050. Samarane, K., Boulif, R., Dhiba, D., Bouhaouss, A., 2018. Improvements and intesification of industrial co-crystallization process for cadmium removal from wet phosphoric acid. Int. J. Eng. Sci. Res. Technol. 7, 152–163. https://doi.org/10.5281/zenodo. 1476369. Saravanan, R., Sacari, E., Gracia, F., Khan, M.M., Mosquera, E., Gupta, V.K., 2016. Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes. J. Mol. Liq. https://doi.org/10.1016/j.molliq.2016.06.074. Touati, M., Benna-Zayani, M., Kbir-Ariguib, N., Trabelsi-Ayadi, M., Buch, A., Grossiord, J.L., Pareau, D., Stambouli, M., 2009. Extraction of cadmium (II) from phosphoric acid media using the di(2-ethylhexyl)dithiophosphoric acid (D2EHDTPA): feasibility
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