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Comparative analysis of arsenates, antimonates and calcium bismuthates based on E–pH diagrams

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Kh.B.Omarov, Z.B.Absat, S.K.Aldabergenova, N.J.Rakhimzhanova, A.B.Siyazova

Ye.A.Buketov Karaganda State University (E-mail: aseka5577@mail.ru)

Comparative analysis of arsenates, antimonates and calcium bismuthates based on E–pH diagrams

The article presents the potential-pH diagram systems Ca–As–H2O, Ca–Sb–H2O, Ca–Bi–H2O and the analy- sis of these systems. The stability region is shown for the followings: Ca3(AsO4)2, Ca3(AsO4)2·4H2O, Ca(AsO2)2, Ca(SbO3)2, Ca2Sb2O7, Ca3(SbO4)2, Ca5Bi14O26, Ca2Bi2O5, CaBi2O4 in oxidizing, recovering and aquatic environments. The data obtained can be used in predicting the occurrence of hydrometallurgical pro- cesses, due to the fact that the E–pH diagram characterizes the behavior of ions in solutions of the com- pounds.

Key words: diagram of the potential–pH, calcium arsenate, calcium antimonate, calcium bismuthate, thermo- dynamic analysis.

During the production of non-ferrous metals, arsenic, antimony and bismuth are considered as bad con- taminants. During copper electrolysis their transition from anode copper in solution happens as a result con- tamination of the electrolyte occurs. The accumulation of significant amounts of harmful impurities in the electrolyte can lead to increased resistance, viscosity of the solution, as well as the overuse of electricity, and therefore, there is a problem of cleaning electrolyte copper production. The world practice for these purposes uses different methods, whereas the analysis shows that there is still a question of purifying electrolyte, as applied methods do not allow to reach deep purity solutions.

The aim of this study is a comparative analysis of arsenates, antimonates and calcium bismuthates in order to predict the behavior of arsenic, antimony and bismuth in the process of hydrolytic precipitation of calcium compounds.

In metallurgy, the main characteristics of hydro and pyrometallurgical processes are thermodynamic quantities of reaction components that enable to predict the direction of the process, the probability of the meeting, under certain conditions, the value of the thermal effect.

Characteristic physicochemical properties of aqueous solutions, which define the process of dissolution and precipitation of various compounds are pH and electrochemical or redox potential (E).

Thermodynamic analysis, based on the construction of diagrams of E–pH is a chemical and thermody- namic basis for addressing assessment of the stability limits of the compounds involved in hydrometallurgi- cal processes to flow any reaction and directed synthesis that allows you to monitor the progress of the pro- cesses and effectively carry out these processes in industrial environments [1, 2].

Arsenic-, antimony- and bismuth containing systems are insufficiently studied, despite the fact that the elements are circulating in many non-ferrous metallurgical processes, complicating the process flow, thereby reducing their cost-effectiveness. In this regard, based on charting E–pH systems of Ca–As–H2O, Ca–Sb–

H2O, Ca–Bi–H2O, we graphically show the stability boundaries and formation of calcium arsenates composi- tion of Ca3(AsO4)2, Ca3(AsO4)2·4H2O, Ca(AsO2)2–H2O, calcium antimonates — Ca(SbO3)2, Ca2Sb2O7, Ca3(SbO4)2 and calcium bismuthates — Ca5Bi14O26, Ca2Bi2O5, CaBi2O4.

Calculated (Table 1) and constructed (Fig. 1) diagram E–pH of the system Ca–As–H2O at standard conditions (25 ºC and 1 atm. Total pressure) by combining the private system diagram As–H2O with private diagram of Ca–H2O is shown.

According to the E–pH diagram of the Ca–As–H2O system forming calcium arsenates in strongly acidic solutions is preferably than arsenite formation of calcium because for deposition of arsenic as calcium arsenite composition Ca(AsO2)2 solution pH should not be lower than 4.26.

Calculated (Table 2) and constructed (Fig. 2) diagram E–pH of the Ca–Sb–H2O at standard conditions (25 °C and 1 atm. Total pressure) by combining the private system diagram of Sb–H2O with private diagram of Ca–H2O is shown.

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Calculation equations o

№ Chemical reaction

1 H2O(L)=O2(g)+4H+(L)+4ē 2 H2(g)=2H+(L)+2ē

3 H3AsO3(L)+H2O(L)=H3AsO4(L)+2H+ 4 H3AsO4(L)=H2AsO4-

(L)+H+(L)

5 H2AsO3-

(L)=HAsO32- (L)+H+(L)

6 HAsO32-

(L)=H+(L)+AsO33- (L)

7 H2AsO3(L)-+H2O(L)=AsO43-

(L)+4H+(

8 HAsO32-

(L)+H2O(L)=AsO43-

(L)+3H+(

9 As(т)+3H2O(L)=НAsO32-

(L)+5H+(L)+3 10 AsO33-

(L)+H2O(L)=AsO43-

(L)+2H+(L)+ 11 As(т)+3H2O(L)=AsO33-

(L)+6H+(L)+3ē 12 HAsO42-

(L)=H+(L)+AsO43- (L)

13 H2AsO4-

(L)=HAsO42- (L)+H+(L)

14 H2AsO3-

(L)+H2O(L)=HAsO42- (L) +3H 15 As(т)+3H2O(L)=H2AsO3-

(L)+4H+(L)+3 16 As(т)+3H2O(L)=H3AsO3(L)+3H+(L)+3 17 AsH3(g)=As(т)+3H++3ē

18 H3AsO3(L)+H2O(L)=HAsO42- (L)+4H+ 19 H3AsO3(L)=H2AsO3-

(L)+H+(L)

20 H3AsO4(L)=H2AsO4-

(L)+H+(L)

21 3Ca2++2H3AsO4=Ca3(AsO4)2+6H+ 22 3Ca(AsO2)2+8H2O=Ca3(AsO4)2+4H 23 Ca2++2H3AsO3=Ca(AsO2)2+2H2O+

24 3Ca2++2H3AsO3+2H2O=Ca3(AsO4) 25 Ca2++2As+4H2O =Ca(AsO2)2+8H+ 26 Ca3(AsO4)2+Ca2++6H2O =

= Ca3(AsO4)2·4 H2O + +Ca(OH)2 + 27 Ca3(AsO4)2·4H2O+2 H2O=3Ca(OH

Figure 1. Diag

of interacting systems Ca(AsO2)2 – Ca3(AsO4)2 – H2

n Electrode rea

E = 1,23–0,059pH E = –0,059pH

(L)+2ē E = 0,586+0,029 lg[H3AsO4]–0,02 lgКр= lg[H2AsO4-]–lg[H3AsO4]–pH lgКр= lg[HAsO32-]–lg[H2AsO3]–pH lgКр= lg[AsO33-]–lg[HAsO32-]–pH

(L)+2ē E = 0,925–0,029 lg[H2AsO3-]+0,02

(L)+2ē E = 0,567–0,029 lg[HAsO32-]+0,02 E = 0,647+0,019 lg[HAsO32-]–0,09 +2ē E = 0,170+0,029 lg[AsO43-]–0,029 ē E = 0,912+0,0196 lg[AsO33-]–0,11

lgКр= lg[AsO43-]–lg[HAsO42-]–pH lgКр= lg[HAsO42-]–lg[H2AsO4-]–p H+(L) +2ē E = 0,585+0,029 lg[HAsO42-]–0,02 E = 0,4085+0,0196 lg[H2AsO3-]–0 E = 0,226+0,0196 lg[H3AsO3]–0,0

E = –0,6268–0,059pH

+(L)+2ē E = 0,858+0,029 lg[HAsO42-]–0,02 lgКр= lg[H2AsO3-]–lg[H3AsO3]–pH lgКр= lg[H2AsO4-]–lg[H3AsO4]–pH lgКр = –3lg[Ca2+]–2 lg[H3AsO4]–6 H3AsO3+4H++4ē E = 0.3354–0.059pH

+2H+ lgКр = –lg[Ca2+]–2 lg[H3AsO3]–2р )2+10H++4ē E = 0.97975–0.1475pH

++6 ē E = 0,34983–0.07867pH

+2H+ lgКр = –lg[Ca2+]–2рН; рН=11,20 H)2+2AsO43-+6H+ lgКр= 2 lg[AsO43-]–6рН; рН=14,2

gram of Е-pH system Ca(AsO2)2 — Ca3(AsO4)2 — H2O

T a b l e 1

2O at 25 ºC action

9 lg[H3AsO3]–0,059pH H; pH=2,19

H; pH=12,10 H;pH=13,41

29 lg[AsO43-]–0,118pH 29 lg[AsO43-]–0,088pH 98pH

lg[AsO33-]–0,059рН 8pH

H; pH=11,51 pH; pH=6,79

29 lg[H2AsO3-]–0,088рН ,078pH

59pH

29 lg[H3AsO3]–0,118рН H; pH=9,24

H; pH=2,19 6рН, pH=2,37 рН pH=4,26

0

O

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Calculation eq

№ Reaction equation

1 H2O(L)=O2(g)+4H+(L)+4ē 2 H2(g)=2H+(L)+2ē

3 Sb(OH)2+ + H2O= Sb(OH)3+H+ 4 Sb + 2H2O= Sb(OH)2++2H++3ē 5 Sb(OH)3+ 3H2O= Sb(OH)6+3H+ 6 Sb + 3H2O= Sb(OH)3+3H++3ē 7 Sb(OH)2+ +4 H2O= Sb(OH)6+4H 8 SbH3= Sb+3H++3ē

9 3Ca2++2Sb(OH)2++4H2O=Ca3(SbO 10 3Ca2++2Sb(OH)3+2H2O=Ca3(SbO4

11 3Ca2++2Sb+8H2O=Ca3(SbO4)2+16H 12 2Ca2++2Sb(OH)2++4H2O=Ca3(SbO 13 2Ca2++2Sb(OH)3+H2O= Ca2Sb2O7+ 14 2Ca2++2Sb+7H2O= Ca2Sb2O7+14H 15 Ca2++2Sb(OH)3=Ca(SbO3)2+6H++4 16 Ca2++2Sb+6H2O= Ca(SbO3)2+12H 17 2Sb+ 3Ca(OH)2+2H2O=Ca3(SbO4) 18 2Sb+ 2Ca(OH)2+3H2O=Ca2Sb2O7+ 19 2Sb+Ca(OH)2+4H2O=Ca(SbO3)2+1

Figu The first two equations are the bility of water (reaction equations 1 actions of Sb–H2O, which shows th Sb(OH)6-, SbH3 and Sb0.

Equations numbered from 9 antimonates (built based on Sb–H2O

quations of interacting systems Ca–Sb–H2O at 25 º

n Electrode rea

E = 1,23–0,059pH E = –0,059pH pH=2,17

E = 0,199 + 0,0197 lg[Sb(OH)2+]–0

++2ē E = 0,729 + 0,118 lg[Sb(OH)6-]–0, E = 0,222–0,059pH

H++2ē E = 0,729 +0,0295 lg[Sb(OH)6-]–0 –0,118pH

E = –0,51–0,0198 lgPSb3–0,059 pH O4)2+12H++4ē E = 0,42–0,0443 lg[Ca2+]–0,0295 l

4)2+10H++4ē E = 0,386–0,0443 lg[Ca2+]–0,148p H++10ē E = 0,386–0,018 lg[Ca2+]–0,094pH O4)2+12H++4ē E = 0,42–0,0443 lg[Ca2+]–0,0295 l

+8H++4ē E = 0,316–0,0295 lg[Ca2+]–0,118p H++10ē E = 0,386–0,018 lg[Ca2+]–0,094pH

E = –0,95–0,0148 lg[Ca2+]–0,089p H++10ē E = 0,23–0,006 lg[Ca2+]–0,071pH

)2+10H++10ē E = –0,120–0,059pH +10H++10ē E = –0,012–0,059pH 10H++10ē E = –0,0944–0,059pH

ure 2. Diagram of Е–pH system Ca–Sb–H2O

equations of the reaction the upper and lower bo , 2). The following reactions at number 3 to 8 me he interaction and existence of dissolved Antimo

to 19 correspond to the reactions of formati O and Ca–H2O systems). In particular the equati

T a b l e 2 C

action

0,039pH 089pH

,0295 lg[Sb(OH)2+]–

H

lg[Sb(OH)2+]–0,177pH H

H

lg[Sb(OH)2+]–0,177pH H

H H

oundaries of the sustaina- eet all the possible inter- ony: Sb(OH)2+, Sb(OH)3,

ion of various calcium ions 9, 10, 11, 17 — the

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boundaries of sustainability of calci bility boundary structure of calcium structure of calcium antimonate Ca(

Calculated (Table 3) and built (25 °C and 1 atm. Total pressure) by of Ca–H2O is shown [3, 4].

Calculation e

№ Reaction equation

1 H2O(L)=O2(g)+4H+(L)+4ē 2 H2(g)=2H+(L)+2ē 3 BiH3 =Bi+3H++3ē 4 Bi=Bi3++3ē

5 Bi3++H2O=BiOH2++H+ 6 2BiOH2++H2O=Bi2O3+4H+ 7 2Bi+3H2O= Bi2O3+6H+ +6ē 8 Bi+H2O= BiOH2++H++3ē 9 2Bi3++5H2O=Bi2O5+10H++4ē 10 2BiOH2++2H2O=Bi2O4+6H++2ē 11 4BiOH2++3H2O=Bi4O7+10H++2ē 12 2Bi2O3+H2O=Bi4O7+2H++2ē 13 2Bi4O7+H2O=2Bi2O4+2H++2ē 14 Bi2O4+H2O=Bi2O5+2H++2ē 15 2Ca2+ +6Bi3++11H2O=Ca2Bi6O11+2 16 2Ca2+ +6Bi0+11H2O=Ca2Bi6O11+22 17 CaBi2O4+Ca2++4Bi3++7H2O=Ca2B 18 Ca2Bi2O5 +4Bi3++6H2O=Ca2Bi6O11

19 Ca5Bi14O26 +2BiOH2++H2O=5Ca2B

Figu The first two equations are the bility of water (reaction equations 1,

ium antimonate structure Ca3(SbO4)2; Equation 1 m antimonateCa2Sb2O7; Equation 15, 16, 19 —

SbO3)2.

(Fig. 3) Diagram E–pH of the system Ca–Bi–H2 y combining the private system diagram of Bi-H

quations of interacting systems Са–Bi–H2O at 25 ºC

n Electrode rea

E = 1,23–0,059pH E = –0,059pH

E = 0,8–0,0591pH–0,0197lgPBiH3

E = 0,215+0,0197lg[Bi3+] lg[BiOH2+]/ lg[Bi3+] = –2,0+pH lg[BiOH2+] = 5,96–2pH E = 0,371–0,0591pH

E = 0,254–0,0197pH+0,0197lg[BiO E = 1,759–0,1477pH–0,0295lg[Bi3 E = 1,792–0,1773pH–0,0591lg[BiO E = 2,042–0,2295pH–0,1182lg[BiO E = 1,338–0,0591pH

E = 1,541–0,0591pH E = 1,607–0,0591pH 22H+ pH = 0,42

2H++18ē E = 0,225–00,072pH i6O11+14H+ pH = 1,0

1+12H+ pH = 1,5 Bi6O11+4H+ pH = 3,73

ure 3. Diagram of Е–pH systems Са–Bi–H2O equations of the reaction the upper and lower bo , 2). The following reactions at number from 3 to

12, 13, 14, 18 — the sta-

— the stability boundary O at standard conditions H2O with private diagram

T a b l e 3 C

action

OH2+]

3+] OH2+] OH2+]

oundaries of the sustaina- o 14 meet all the possible

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interactions of the system Bi–H2O, which shows the interactions and existence of bismuth ions: Bi0, Bi3+, BiOH2+, BiH3 and bismuth oxide Bi2O3, Bi4O7, Bi2O4, Bi2O5.

Equations under the number of 15 to 19 corresponds to the region of existence of calcium bismuthates (systems are built based on Bi–H2O and Ca–H2O), in particular, the equations 15 and 16 — the existence of the border calcium bismuthate composition Ca2Bi6O11. Dash-dotted lines correspond to the boundaries of possible transition bismuthate calcium Ca2Bi6O11 the next bismuthates: CaBi2O4 (reaction equation 17), Ca2Bi2O5 (reaction equation 18), Ca5Bi14O26 (reaction equation 19).

Such bismuthates as Ca3Bi4O9, Ca7Bi6O16, Sa7Bi10O22, which subject to limiting interactions of Bi–H2O system and Ca–H2O, on this chart are not reflected.

Based on the analysis of the set of diagrams results show that arsenates, antimonates and calcium bismuthates are stable compounds in oxidized, recovered and aqueous media. Calcium arsenate are stable in an oxidizing environment at E > 0,4 V and the pH range of 2–14; calcium antimonates and calcium bismuthates — throughout the whole pH range. Increase in the number of metal properties in As–Sb–Bi leads to increase of the stability region in the row arsenate – antimonate – calcium bismuthate in acid areas.

References

1 Справочник химика / Под ред. Б.П.Никольского. — Т. 3. — Л.: Наука, 1951. — 1150 с.

2 Касенов Б.К., Алдабергенов М.К., Пашинкин А.С. Термодинамические методы в химии и металлургии. — Алматы:

Рауан, 1994. — 126 с.

3 Гаррелс Р.И., Крайст И.А. Растворы, минералы, равновесия. — М.: Мир, 1968. — 386 с.

4 Матаев М.М., Алдабергенов М.Қ., Абдраимова М.Р., Досжанова Н.А. СаО–Fe2O3–Bi2O3 — жүйесінің триангуляция- сы // Теоретическая и экспериментальная химия: Материалы IV Междунар. науч.-практ. конф., посвящ. 80-летию проф.

М.И.Бакеева. — Караганда, 2010. — С. 223–227.

Х.Б.Омаров, З.Б.Абсат, С.К.Алдабергенова, Н.Ж.Рахимжанова, А.Б.Сиязова

Кальцийдің арсенаттарын, антимонаттарын жəне висмутаттарын

Е–рН диаграммасы негізінде салыстыра отырып талдау

Мақалада Ca–As–H2O, Ca–Sb–H2O, Ca–Bi–H2O жүйелерінің Е–рН диаграммасы көрсетілген жəне оған талдау жүргізілген. Ca3(AsO4)2, Ca3(AsO4)2·4H2O, Ca(AsO2)2, Ca(SbO3)2, Ca2Sb2O7, Ca3(SbO4)2, Ca5Bi14O26, Ca2Bi2O5, CaBi2O4 сияқты тұрақты қосылыстардың тұрақтылық аймағы белгіленген.

Мақаладағы мəліметтер гидрометаллургия саласында өте қызықты болып табылады, себебі Е–рН диаграммасы иондар мен қосылыстардың ерітіндідегі қасиетін сипаттайды.

Х.Б.Омаров, З.Б.Абсат, С.К.Алдабергенова, Н.Ж.Рахимжанова, А.Б.Сиязова

Сравнительный анализ арсенатов, антимонатов и висмутатов кальция

на основе диаграммы Е–рН

В статье представлены диаграммы потенциал–рН систем Ca–As–H2O, Ca–Sb–H2O, Ca–Bi–H2O и про- веден анализ данных систем. Показаны области устойчивости Ca3(AsO4)2, Ca3(AsO4)2·4H2O, Ca(AsO2)2, Ca(SbO3)2, Ca2Sb2O7, Ca3(SbO4)2, Ca5Bi14O26, Ca2Bi2O5, CaBi2O4, которые являются устой- чивыми соединениями. Данные статьи представляют интерес в гидрометаллургических процессах, в связи с тем, что диаграмма Е-рН характеризует поведение ионов, соединений в растворах.

References

1 Chemist reference book, Ed. B.P.Nikolsky, Leningrad: Nauka, 1951, 1150 p.

2 Kasenov B.K., Aldabergenov M.K., Pashinkin A.S. Thermodynamic methods in chemistry and metallurgy, Almaty: Rauan, 1994, 126 p.

3 Garrels R.I., Christ I.A. Solutions, minerals, equilibrium, Moscow: Mir, 1968, 386 p.

4 Matayev M.M., Aldabergenov M.K., Abdraimova M.R., Doszhanova N.A. Theoretical and Experimental Chemistry: Materials of IV International scientific-practical conference dedicated to 80th anniversary of prof. M.I.Bakeev, Karaganda, 2010, p. 223–227.

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