Shiva Prasad

The process of biosorption of heavy metals in bioreactors loaded with sanitary sewage sludge

This work on the process of biosorption of nickel and chromium in an ascendant continuous-flow, fixed packed-bed bioreactor of sanitary sewage sludge was conducted in a search for solutions to the environmental problem caused by heavy metals. Analysis of the results demonstrated that the absorbent had an extraordinary capacity for biosorption of the heavy metals studied at about 9.0 pH of the effluent, with a removal percentage of over 90.0% for the two metals. Chemometric study results demonstrated that 20 days of the experimental system function were sufficient for achieving the maximum efficiency of sorption of the heavy metals studied by the sanitary sewage sludge employed.

Tratamento de resíduos sólidos de centrais de abastecimento e feiras livres em reator anaeróbio de batelada

Significant quantity of organic solid waste with favorable characteristics for integral utilization in anaerobic biostabilization is produced in free markets and supply centers. The process is conducted in anaerobic batch reactors (ABR), with detention time of solids varying from 250 to 300 days, producing biogas with about 60% of methane, besides the partially biostabilized organic compost as the final product. In this study, the organic solid waste used was typically of vegetables, originated from the supply centers, free markets and sanitary wastewater sludge. The experimental system used was basically constituted of a batch anaerobic reactor of 2200 L capacity, besides the other complementary devices. The experimental system was installed and monitored during the period of January to September 2001 at the Experimental Station for Biological Treatment of Sanitary Sewage, located at Tambor, Campina Grande, in the State of Paraiba, Brazil. During the process of monitoring the systematic characterization of the solid, liquid and gaseous fractions were realized. After analyzing the data, the feasibility of this alternative treatment, was evidenced although the economic viability in comparison to other technological alternatives of treatment of organic solid waste remains to be tested.

Otimização do banho eletrolítico da liga Fe-W-B resistente à corrosão

A study on optimization of bath parameters for electrodeposition of Fe-W-B alloys from plating baths containing ammonia and citrate is reported. A 23 full factorial design was successfully employed for experimental design analysis of the results. The corrosion resistance and amorphous character were evaluated. The bath conditions obtained for depositing the alloy with good corrosion resistance were: 0.01 M iron sulfate, 0.10 M sodium tungstate and 0.60 M ammonium citrate. The alloy was deposited at 12% current efficiency. The alloy obtained had Ecorr -0.841 V and Rp 1.463 x 104 Ohm cm2. The deposit obtained under these conditions had an amorphous character and no microcracks were observed on its surface. Besides this, the bath conditions obtained for depositing the alloy with the highest deposition efficiency were: 0.09 M iron sulfate, 0.30 M sodium tungstate and 0.50 M ammonium citrate. The alloy was deposited at 50% current efficiency, with an average composition of 34 wt% W, 66 wt% Fe and traces of boron. The alloy obtained had Ecorr -0.800 V and Rp 1.895 x 103 Ohm cm2. Electrochemical corrosion tests verified that the Fe-W-B alloy deposited under both conditions had better corrosion resistance than Fe-Mo-B.

Estudo termogravimétrico do processo de sorção de metais pesados por resíduos sólidos orgânicos

Pollution of a hydrographic basin can cause alterations in physical, chemical and biological properties of water mass, committing its use for the human consumption and for other types of activities, depending on the contamination or pollution level. The conventional treatment methods for effluents containing heavy metals produce significant amounts of byproducts with recalcitrant characteristics; besides the techniques being onerous their reproducibility is low. The search for cheaper and definitive solutions led to the development of clean technologies, among these technologies the sorption process based on utilization of absorbent substances for these elements can be pointed out. This work has the objective of evaluating the sorption process of heavy metals by organic solid waste utilizing the thermogravimetric technique. The results obtained demonstrated that the profiles of the thermogravimetric curves of the organic solid waste presented significant modifications in the physical and chemical characteristics when submitted to the heavy metal sorption process.

Potentiometric and conductometric studies on the system acid-isopolytungstate and the formation of lanthanum tungstates

The stoichiometry of the polyanions formed by the action of nitric acid on sodium tungstate (≤ 0.01M) has been studied by means of electrometric techniques involving pH-potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves provide evidence for the existence of the polyanions, para-W12O41 10- and meta-W12O39 6- corresponding to the ratio of H+:WO 4 2- as 7:6 and 9:6 in the pH ranges 5.7-6.0 and 3.6-4.1, respectively. The interaction of lanthanum nitrate with sodium tungstate solutions, at specific pH levels 8.0, 5.9 and 4.0 was also studied by pH and conductometric titrations, in aqueous and alcoholic media, with each of the reagents alternatively used as titrant. The electrometric experiments provide definite evidence of the formation of normal-La2O3.3WO3, para-5La2O3.36WO3 and meta-La2O3.12WO3 tungstates in the vicinity of pH 6.3, 5.0 and 4.2, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.

Thermal analysis of the powder and the bran of algaroba

The powder and the bran of algaroba pods, submitted to drying temperatures of 55, 65, 75, 85, 95 and 105°C, were studied by conventional and thermogravimetric methods. The dynamic thermogravimetric curves of the samples indicated the following thermal stability order: 105>55>65>95>85>75°C. The powder and the bran of algaroba pods, dried at 55°C, presented protein content higher and isothermal thermogravimetric profiles comparable. The calorimetric curves of samples, dried at 55°C, indicated the gelatinization of starch.

Revestimento eletrolítico com uma liga amorfa de Ni-W-B, resistente à corrosão e ao desgaste

The process of electrodeposition of amorphous layer of Ni-W-B alloy on a cathode, using a bath containing 0.0185 M nickel sulfate, 0.0155 M sodium tungstate, 0.0364 M sodium citrate, 0.017 g/L 1-dodecylsulfate-Na and ammonia for pH adjustment to 8.5, has been studied. Detailed studies on bath temperature, bath agitation and cathode current density led to the optimum conditions for obtaining satisfactory alloy deposit. The alloy presented higher corrosion and wear resistance in comparison to the hard chromium, besides its amorphous characteristic verified by X-ray diffraction. These alloys should have great importance in various applications in chemical, petroleum, petrochemical, naval, automobile and civil construction industries due to their special characteristics such as high wear and corrosion resistance and the capacity to maintain their mechanical properties at high temperatures.

Electrometric investigations on formation of lanthanum molybdates as a function of Ph

The precise nature of the reaction between lanthanum nitrate and sodium molybdate at specific pH levels 7.6, 5.5 and 4.1 has been studied by means of electrometric techniques involving potentiometric and conductometric titrations, in aqueous and alcoholic media using each reagent as titrant. Well-defined breaks and inflections in the titration curves provide cogent evidence for formation and precipitation of lanthanum normal-La2O3.3MoO3, para- La2O3.7MoO3 and octa-2 La2O3.24MoO3 molybdates in the vicinity of pH 5.9, 4.8 and 4.2, respectively. Analytical investigations of the precipitates of lanthanum molybdates have also been carried out, which substantiate the results of the electrometric study.

Electrometric studies on formation of cerium vanadates as a function of pH

A natureza precisa da reacao entre solucoes de acido nitrico e de ortho-vanadato de sodio foi estudada por tecnicas electrometricas envolvendo titulacoes potenciometricas e condutometricas. As inflexoes e degraus bem definidas nas curvas de titulacoes confirmaram a existencia de anions, piro-V2O74-, meta-VO3- e poli-H2V10O284- correspondendo as razoes de VO43-:H+ como 1:1, 1:2 e 1:2,6 na vizinhanca do pH 10,5; 7,4 e 3,6, respectivamente. Ainteracao entre solucoes de nitrato de cerio(III) e vanadato de sodio a especificos niveis de pH 12,4; 10,5; 7,4 e 3,6 tambem foi estudada por titulacoes potenciometricas e condutometricas entre os reagentes. Os pontos finais obtidos a partir de inflexcoes nitidas nas curvas de titulacoes forceram evidencias incontestaveis sobre a formacao e precipitacao de vanadatos orto-Ce2O3.V2O5, piro-2Ce2O3.3V2 O5 e meta-Ce2O3.3V2O5 de cerio nas proximidades dos valores de pH 7,4; 6,2 e 4,8, respectivamente. Investigacoes analiticas sobre os precipitados formados confirmam os resultados do estudo eletrometrico.

Formation of Nickel Vanadates as a Function of pH

The precise nature of the reaction between hydrochloric acid and sodium ortho-vanadate solution has been studied by means of electrometric techniques involving potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves confirm the existence of the anions, pyro-V2O74- , meta-VO3- and poly-H2V10O284- corresponding to the ratios of VO43-:H+ as 1:1, 1:2 and 1:2.6 in the neighborhood of pH 10.5, 7.4 and 3.6, respectively. The interaction of nickel chloride with sodium vanadate solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also studied by potentiometric and conductometric titrations between the reactants. The end-points obtained from the sharp inflections in the titration curves provide definite evidence for the formation of ortho-3NiO.V2O5, pyro-2NiO.V2O5 and meta-NiO.V2O5 vanadates of nickel in the vicinity of pH 8.9, 8.0 and 6.8, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.