Intensification of zinc dissolution process in sulphuric acid

Many high purity salts are produced by dissolving pure metal in non-oxidizing mineral acids. If hydrogen overpotential on the given metal is high, then the rate of overall process is defined by reaction of hydrogen ion reduction. This study investigated the possibility of accelerated dissolving of metal zinc in sulphuric acid by introducing copper cathode on which evolving hydrogen is much easier than on zinc. It was found out that the acceleration of zinc dissolving is possible and, at constant surface of copper cathode depends on the quality of electrical contact between copper electrode and zinc

Određivanje sadržaja fluorida u vodi za piće i čajevima fluorid-selektivnom elektrodom

Potentiometric analysis of fluoride content (as F- ion) in solutions by using fluoride ion-selective electrode is simple, reliable and cheap. Very small concentrations of fluoride-ions (to 10-6 mol/dm3) can be determined by fluoride selective electrode, with regulation of ion strength of a solution and control of concentration of hydroxide ions and interfering ions of metals. The influence of pH and complexing ions of metals can be successfully regulated by the TISAB solution and by preserving pH value in the range from 5.00 to 7.00. The content of fluorides in the samples can be determined by the method of direct potentiometer, and in the case of very low concentration by standard addition method. In this paper it was analyzed the determination of fluoride ions concentration in bottled mineral waters and water from Belgrade plumbing in two Belgrade districts (Palilula and Novi Beograd) and in tea, by using the fluoride selective electrode. It was determined that the content of fluoride ions in bottled mineral water significantly differs from values given on declaration, and that content of fluoride ions varies over a period of time. The content of fluoride ions in water from plumbing in two Belgrade districts at the time of analysis was significantly increased and exceeded values given in Regulation for drinking water quality. The received results from the analysis of fluorides in teas show that fluorides exist in teas in different concentrations. There are also differences between the same kinds of tea, which is noted with mint (Mentha piperitae folium), as a consequence of differences between soils where it was planted. As taking of fluorides, according to World Health Organisation recommendation (WHO), is limited in the range from 2 to 4 mg per day, it is necessary to give the content of fluorides on all products that are used in human consumption.Potenciometrijsko određivanje sadržaja fluorida (kao F-jon) u rastvorima upotrebom fluoridne jon-selektivne elektrode je jednostavno, pouzdano i jeftino. Fluorid-selektivnom elektrodom mogu se odrediti veoma niske koncentracije fluorid-jona (do 10-6 mol/dm3), uz regulisanje jonske jačine rastvora i kontrolisanje koncentracije hidroksid-jona i interferirajućih jona metala. Uticaj pH i kompleksirajućih jona metala može se uspešno regulisati rastvorom TISABa i održavanjem pH vrednosti u oblasti od 5,00 do 7,00. Sadržaj fluorida u uzorcima može se odrediti metodom direktne potenciometrije, a u slučaju veoma niskih koncentracije, metodom standardnog dodatka. U radu je vršeno određivanje koncentracije F--jona u flaširanim mineralnim vodama ('Vujić voda', 'Rosa', 'Duboka', 'Voda-voda', 'Aqua viva', 'Knjaz Miloš') i vodi iz beogradskog vodovoda sa dve beogradske opštine (Palilula i Novi Beograd) i u čajevima (Divlja nana (Mentha piperitae folium), Čaj od žalfije (Salviae officinalis), Čaj od kantariona (Hypericum perforatum), 'Domaća nana' (Mentha piperita L.), Čaj od kamilice (Chamomillae flos)), upotrebom fluorid-selektivne elektrode. Uočeno je da sadržaj fluorid-jona u flaširanim mineralnim vodama znatno odstupa od vrednosti koje su date na deklaraciji, ali i da sadržaj fluorid-jona varira tokom vremena. Sadržaj fluorid-jona u vodi iz vodovoda sa dve beogradske opštine, u vreme analiziranja je znatno povećan i premašuje vrednosti propisane Pravilnikom o kvalitetu vode za piće. Dobijeni rezultati ispitivanja fluorida u čajevima ukazuju da se fluoridi nalaze u čajevima u različitim koncentracijama. Do razlike dolazi i među istim vrstama čaja, što je zabeleženo kod nane (Mentha piperitae folium), što je posledica pre svega zemljišta na kojem je nana uzgajana. Kako je, saglasno preporukama Svetske zdravstvene organizacije (SZO), unošenje fluorida limitirano u opsegu 2 do 4 mg dnevno, na svim proizvodima koji se koriste u humanoj upotrebi potrebno je navesti i sadržaj fluorida

Study of corrosion resistance of chromium-nickel steel in calcium - hypochlorite solution. Part 1. Steels uranus b6

Corrosion resistance of Cr - Ni (special steels) specimen is tested by electrochemical methods, numerical method of linear polarization and polarization resistance method in calcium-hypochlorite (Ca(OCl)2) solutions. With increasing of Ca(OCl)2 concentration, pH value of the solution increases, as well as active chlorine concentration and corrosion activity of the medium. According to the quantitative method of the corrosion resistance determination it can be concluded that the steels tested in 1 wt % Ca(OCl)2 solution are resistant, in 10 wt % solution constant, and in 50 wt % suspension less resistant. URANUS B6 showed the best corrosion resistance of all tested chromium - nickel steels in all tested corrosion mediums

Primena bakar-selektivne elektrode tipa prekrivena žica za određivanje bakra(II) potenciometrijskom titracijom sa etilendiaminom u vodenim i nevodenim rastvorima

In this work, potentiometric titrations of the solution of the Cu(II) ione have been executed with ethylenediamine as complexing agent and the copper selective electrode coated wire type/SCE indicator system in aqueous and nonaqueous solvents. Because of the difficult conditions of the forma­tion of the Cu (II) ethylenediamine complex, due to the presence of parallel reactions influencing the position of the basic balance of the formation of the complex, this study discusses and deduces the equations for the calculation of the constant of the formation of the complex as well as the equations for the calculation of the free ethylenediamine. In all the cases a pronounced extreme of the curve of titration has been remarked in the final phase of the titration, whatever diluent was used. Similar results have been obtained using solvents such as: water, alcohol (methanol, ethanol, buthanol), which was expected having in mind the chemical resemblance of these compounds (polar mollecules), while a sharper extreme was obtained in N,N-dymethylformamide, which was expected as well because of the similar basic characteristics with ethylenediamine. The results obtained by this study show the exceptional advantage of ethylenediamine as complexing agent and also the possibility of the application of the copper selective electrode coated wire type/SCE indicating system for the determina­tion of Cu(II) in aqueous and non-aqueous solvents and for the determination of the constants of the determination of the formation of the ethylenediamine complex. .Formiranje kompleksa Cu(II) sa etilendiaminom otežano je postojanjem paralelnih ravnoteža sa reaktantima, koji reagujući sa ligandom, etilendiaminom, ili Cu(II) jonom utiču na položaj osnovne ravnoteže građenja kompleksa. Polazeći od konstatacije da svojstva etilendiaminada gradi stabilne komplekse sa mnogobrojnim jonima u analitičkoj hemiji nisu dovoljno iskorišćena, u ovome radu izvršena je analiza mogućih efekata na položaj ravnoteže građenja kompleksa kao i izvođenje jednačina za ukupnu konstantu obrazovanja B2 i za izračunavanje koncentracije slobodnog etilendiamina. U radu su izvršena potenciometrijska ispitivanja rastvora Cu(II) jona sa etilendiaminom kao kompleksirajućim agensom uz bakar-selektivna elektroda/zasićena kalomelova elektroda (ZKE) indikatorski sistem u vodenim i nevodenim rastvorima. Dobijeni rezultati pokazali su izuzetnu vrednost etilendiamina kao kompleksirajućeg agensa u poređenju sa drugim, konvencionalnim kompleksirajućima agensima, a takođe i mogućnost primene bakar-selektivna elektroda/ZKE indikatorskog sistema za određivanje konstante obrazovanja Cu(en)22+ kompleksa.

Određivanje titracione kiselosti u belom vinu

The amount of titration acid in must is in the largest number of cases with in the range 5.0-8.0 g/dm3. Wines, as a rule, contain less acids than must, and according to Regulations, titratable acidity is in the range of 4.0-8.0 g/dm3 expressed in tartaric acid, because a part of tartaric acid is deposited in the form of salts (tartar or argol) during alcohol fermentation. For wines that contain less than 4 g/dm3 of titratable acids there arises a suspicion about their origin, that is, that during the preparation some illegal acts were done. Because of that, the aim of this paper is to determine titratable acidity in white wine, using standard methods of determination, which are compared with the results received by potentiometric titration using ion-selective electrode. According to the received results it can be seen that wine titration with indicator gives sufficient reliable values of wine titration acidity. However, as potentiometric titration at pH value 7.00 is more reliable and objective method, the values of titratable acids content in wine, expressed through tartaric acid, are given according to this result. The analysis of differential potentiometric curves shows that these curves can give us an answer to the question of the presence of a larger amount of other nonorganic substances, which have already existed in wine. However, none of the used methods gives absolutely reliable answer what substances are present in analysed samples.Količina titracionih kiselina u širi se, u najvećem broju slučajeva, kreće između 5 i 8 g/dm3. Vina, po pravilu, sadrže nešto manje kiselina nego šira, a prema Pravilniku, titraciona kiselost se kreće između 4,0 i 8,0 g/dm3 izraženo u vinskoj kiselini, jer se deo vinske kiseline istaloži u obliku soli (streša) u toku alkoholne fermentacije. Za vina koja sadrže ispod 4 g/dm3 titracionih kiselina postoji sumnja u njihovo poreklo, tj. da su prilikom njihovog spravljanja vršene nedozvoljene radnje. Zbog toga je cilj rada bio da se izvrši određivanje titracione kiselosti u belom vinu, standardnim metodama određivanja koje su upoređene sa rezultatima dobijenim potenciometrijskom titracijom uz jon-selektivnu elektrodu. Na osnovu dobijenih rezultata uočava se da titracija vina uz indikator daje dovoljno pouzdane vrednosti titracione kiselosti vina. Međutim, pošto je potenciometrijska titracija, pri pH vrednosti 7,00, pouzdanija i objektivnija metoda, vrednosti za sadržaj titracionih kiselina u vinu, izraženih preko vinske kiseline, date su upravo na osnovu ovog rezultata. Analiza diferencijalnih potenciometrijskih krivih, ukazuje da ove krive mogu pružiti odgovor na pitanje o prisustvu veće količine drugih neorganskih supstanci, koje se već nalaze u vinu. Međutim, ni jedna od ispitivanih metoda ne daje dovoljno pouzdan odgovor koje supstance su prisutne u analiziranim uzorcima, već odgovor na ovo pitanje može pružiti jedino metoda jonske hromatografije

The influence of powder particle size on properties of Cu-Al2O3 composites

Inert gas atomized prealloyed copper powder containing 2 wt.% Al (average particle size ≈ 30 μm) and a mixture consisting of copper (average particle sizes ≈ 15 μm and 30 μm) and 4 wt.% of commercial Al2O3 powder particles (average particle size ≈ 0.75 μm) were milled separately in a high-energy planetary ball mill up to 20 h in air. Milling was performed in order to strengthen the copper matrix by grain size refinement and Al2O3 particles. Milling in air of prealloyed copper powder promoted formation of finely dispersed nano-sized Al2O3 particles by internal oxidation. On the other side, composite powders with commercial micro-sized Al2O3 particles were obtained by mechanical alloying. Following milling, powders were treated in hydrogen at 400 0C for 1h in order to eliminate copper oxides formed on their surface during milling. Hot-pressing (800 0C for 3 h in argon at pressure of 35 MPa) was used for compaction of milled powders. Hot-pressed composite compacts processed from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800°C for 1 and 5h in argon) in order to examine their thermal stability. The results were discussed in terms of the effects of different size of starting powders, the grain size refinement and different size of Al2O3 particles on strengthening, thermal stability and electrical conductivity of copper-based composites

Uticaj aditiva na brzinu korozije limenke napunjene komadima kajsije

Polarization techniques are used for testing the impact of different compounds (additives) on tinplate corrosion, using pieces of apricot dipped in syrup with and without nitrate addition as electrolyte solution, at the same time using filled cans as electrolytic cell and operating electrode. This procedure determined the intensity of inhibiting tin dissolving with some of the used additives like sodium-benzoate, potassium-sorbate sodium-lauril-sulphate and p-aminobenzoate acid. Adding these additives to canned pieces of apricot in syrup led to inhibiting of tin dissolving, which was experimentally proved.Primenom polarizacionih tehnika ispitivan je uticaj različitih supstanci (aditiva) na koroziju belog lima od kojeg su napravljene limenke primenjujući kao rastvor elektrolita komade kajsije u sirupu sa i bez dodatka nitrata, uz istovremeno korišćenje napunjene konzerve kao elektrolitičke ćelije i kao radne elektrode. Ovim postupkom je određena jačina inhibiranja rastvaranja kalaja nekim od primenjenih aditiva, kao što su: natrijum-benzoat, kalijum-sorbat, natrijum-lauril-sulfat i p-amino-benzoeva kiselina. Dodatkom ovih aditiva u konzervisane komade kajsije u sirupu došlo je do inhibiranja rastvaranja kalaja što je eksperimentalnim putem i dokazano

A NEW PROCEDURE FOR OBTAINING CALCIUM SULPHATE α-HEMIHYDRATE ON THE BASIS OF WASTE PHOSPHOGYPSUM

Investigations, conducted in this study showed that waste phosphogypsum-dihydrate represents a burden which even must not be kept in deposits because of its large quantity in relation to the main product – phosphoric acid, as well as because of great impact of a phosphogypsum deposit on the environment. By the proposed procedure, calcium-sulphate dehydrate is transformed into a far purer α-hemihydrate which, with its physic-chemical characteristics, approaches natural gypsum and contains additional components which enable formation of small-grain phosphogypsum which may be utilised in construction industry. Test installation, given in this study, is highly automated and designed in such way to be operated by only one person. The obtained α-hemihydrate may be utilised for obtaining of gypsum blocks and dry hemihydrat

Primena metode atomske apsorpcione spektrofotometrije (AAS) za određivanje sadržaja teških metala u fosfogipsu

Phosphogypsum is formed as a by-product in the process of 'green' phosphoric acid production. This is done in the so called 'wet process' by the action of sulphuric acid on raw phosphate at low temperature ( lt 100 °C). Despite the same molecular formula and marked similarity with natural gypsum, phosphogypsum contains more than 50 impurities, and this is directly connected with the type of phosphate used in the production cycle. The aim of this paper was to consider the possibility of using phosphogypsum for amelioration of solonetz soil, bearing in mind its content of heavy metals, which are rather toxic for human organism and which can be transferred from soil to various plants used in human nutrition. On the other hand, there are very few data in the literature about the determination of heavy metals in phosphogypsum. The content of heavy metals in phosphogypsum was determined by atomic absorption spectrophotometry because this method has broad application in ana­lytical practice due to its high sensitivity, selectivity and precision. The results of the investigation indicate the following average content of heavy metals (in ppm): Fe-785, Pb-45, Zn-45, Cd-7, Mn-8, Co-10, Ni-20 and Cu-17. For the investigation of the effect of phosphogypsum on solonetz soil the following points were taken into consideration: maximum recommended dose of phosphogypsum (7 t/ha) for the amelioration of solonetz soil and the weight of soil layer (from 0 to 20 cm) having an area of 1 ha. The results obtained indicate that the amounts of heavy metals that are introduced into the soil with 7 t/ha of phosphogypsum are in the range from 0.035 to 0.8% of their maximum permissible content for arable soils. This means that only long-term application of phosphogypsum would introduce significant amounts of these elements into the soil.Procesom dobijanja 'zelene' fosforne kiseline tzv. 'mokrim postupkom', dejstvom sumporne kiseline na sirovi fosfat na niskoj temperaturi ( lt 100 °C) kao nus-proizvod nastaje - fosfogips (sa faktorom 5:1, u odnosu na H3PO4). Uprkos istoj molekulskoj formuli i izraženoj sličnosti sa prirodnim gipsom, fosfogips sadrži preko 50 vrsta nečistoća, što je u direktnoj vezi sa vrstom fosfata koji je korišćen u proizvodnom ciklusu. Cilj rada bio je razmatranje mogućnosti primene fosfogipsa za melioraciju soloneca, sa aspekta sadržaja teških metala, koji su izuzetno toksični i kumulativni za čovekov organizam, a iz zemljišta prelaze u biljke, kojima se čovek hrani. Sa druge strane, u literaturi se nalaze veoma oskudni podaci o ispitivanju sadržaja teških metala u fosfogipsu. Sadržaj teških metala u fosfogipsu određivan je metodom atomske apsorpcione spektrofotometrije (AAS), budući da je to metoda koja je našla veliku primenu u praksi usled visoke osetljivosti, selektivnosti i preciznosti. Rezultati ispitivanja su pokazali sledeći sadržaj teških metala (u ppm): Fe-785, Pb-45, Zn-45, Cd-7, Mn-8, Co-10, Ni-20, Cu-17. Za ispitivanje uticaja primene fosfogipsa za melioraciju soloneca, uzeta je u obzir preporučena maksimalna norma za gipsovanje soloneca od 7 t/ha zemljišta i težina sloja debljine od 0 do 20 cm a površine 1 ha. Dobijeni rezultati su pokazali da se preporučenom maksimalnom normom za gipsovanje soloneca fosfogipsom unosi po 1 ha zemljišta od 0,035 do 0,8% od maksimalno dozvoljenog sadržaja teških metala - MDK vrednosti, što znači da bi tek višegodišnjom upotrebom fosfogipsa došlo do unošenja značajnijih količina ovih elemenata u zemljište. Kako se proces melioracije soloneca najčešće vrši u intervalu od 5 do 6 godina, unošenje teških metala bilo bi u zanemarljivoj količini i bez uticaja na životnu sredinu