Lorenzo Liberti

Exchange equilibria on anion resins

Abstract Selectivity coefficients, free exchange energies and enthalpies between 5°C and 45°C of different anion resins with functional groups of the amino type were determined for the SO−4/Cl− system in a range of bulk salinities lying between 6 x 10−3 and 2.4 N The experimental results showed that the selectivity for the bivalent ion depends strongly on the basicity of the resin, the affinities of the various amino functional groups following the order primary > secondary > tertiary > quaternary. Furthermore, the affinity of every resin for the sulphate ion increases with the dilution of the aqueous phase and with the equilibrium temperature. These results are in full agreement with the theoretical forecasts, and show that in heterovalent exchange processes a fundamental role is played by the phenomena connected with the electrostatic interactions.

Phosphates and ammonia recovery from secondary effluents by selective ion exchange with production of a slow-release fertilizer

A process for the reduction of eutrophic potential in urban secondary effluents. which comprises the selective exchange of phosphates on a weak anion resin and of ammonia on clinoptilolite, is described. Sodium chloride is used to regenerate both resins, with some Ca(OH)2 added for clinoptilolite. By adding Mg(OH)2, eventually precipitated with lime from sea water, the premium quality, slow-release fertilizer MgNH4PO4-6H2O is recovered from the concentrated regeneration streams, which can then be recycled. Laboratory evaluations of the hydrolysis extent of the weak anion resin in the presence of bicarbonates showed that a steady-state is attained with resin exchange capacity reproducibly averaging about 80 mmol phosphates 1,−. The preliminary runs on a pilot plant for the tertiary treatment of urban sewage are also presented.

Chloride/sulfate exchange on anion resins. Kinetic investigations. II. Particle diffusion rates

Abstract The exchange rates for the chloride to sulfate conversion on several anion resins, when particle diffusion is the rate determining step, have been measured, using the stirrer-reactor technique and infinite solution volume conditions. The interdiffusion coefficients resulted to be variable, depending mainly on the conversion degree of the resin. Two approaches have been used to calculate the exchange rates. The first one, based on the simpler rate laws for isotopic exchanges, allowed the exchange kinetics to be anticipated by the aid of a semiempirical equation for the interdiffusion coefficient. According to the second procedure, the single ion diffusion coefficients, calculated as limiting values of the (apparent) interdiffusion coefficients, and the more rigorous Nernst-Planck model for ion exchange processes were applied. Both approaches showed a satisfactory agreement between calculated and experimental kinetics.

Selective renovation of eutrophic wastes—phosphate removal

Abstract This is the first part of a basic investigation concerning the multicomponent chloride/sulfate/phosphate/nitrate equilibrium on anion resins. The study is to throw more light on the fundamentals of poly-anions, heterovalent equilibria on anion resins, and to develop a selective process to remove eutrophic species from sewage effluents. In this paper the chloride/phosphate equilibrium is described for a large selection of different anion resins and the selectivity dependence on several external (i.e. solution pH, concentration and composition) or internal (i.e. resin basicity, porosity, matrix etc.) parameters evaluated.

Sulphate removal and dealkalization on weak resins of the feed water for evaporation desalting plants

Abstract A process for the sulphate removal from the sea water fed to an evaporation plant by means of a weak anion exchange resins plant has been tested both in laboratory and pilot plant scales. The evaporation plant has been operated for 7500 hours at temperatures up to 145°C and with concentration factors varying between 2.0 and 2.5. No scales on the exchange surfaces were observed at any time.

Thermoanalytical study of activated carbon regeneration. I. Desorption of phenol and aniline

Abstract During a thermoanalytical investigation to determine the mechanism and desorption energies of common pollutants, a complex pattern has been demonstrated when activated carbon loaded with phenol or aniline is heated up to 950°C in a dynamic nitrogen atmosphere. Water is completely removed before 150°C. Four and three consecutive steps appear when phenol and aniline are released, respectively.

Chloride/sulfate exchange on anion resins. Kinetic investigations. Chemical control in selective exchanges

Abstract Rate determinations for the Cl-/SO=4 exchange on anion resins in very diluted systems (1 ÷ 6 × 10-3N), where resin selectivities for the divalent ion are drastically raised by the electroselectivity effect, show convincing evidence that the chemical reaction rate on fixed charges controls the overall process kinetics. Activation energies, in particular, (up to 16.83 kcal/eq) are definitely out of the range for usual diffusion-controlled kinetics. A spherically-symmetrical diffusion model with a billiard-ball-like mechanism of site-to-site jumping of ions inside the resin is suggested.

Results of four years of operation at high temperature(150°C) of Bari's desalination plant.

Abstract A general description of the 0.5 MGPD (1900 m 3 /d) high temperature MSF plant 1 in Bari, designed and built by REGGIANE O.M.I., is given. The plant has an acid treatment with sea water desulphation made by anion exchange resins to allow operation at high temperature (top brine temperature of 302°F, or 150°C) and high brine concentration without CaSO 4 scale. Results and data collected after approx. 4 years of plant operation are presented, including interesting aspects of the desulphation process, such as the dealkalization reaction and the system convergence at start-up.

Advanced evaporation plants with sulfate removal by ion exchange

Abstract Two new distillation plants are going into operation in Italy. The first, located in the town of Bari, is an high temperature multi-stage flash, with production rate of l700 m3/d, top brine temperature of 150°C and performance ratio of 19 kg fresh water per kg steam. The second is a vapor-compression, vertical tube evaporator, with a 240 m3/d production rate at 105°C and electric energy consumption of 14 kWh/m3. These plants are coupled with an ion exchange pretreatment unit, where bicarbonates and sulfates are partially exchanged with chlorides by means of a weak anion resin regenerated with brine; alkaline (CaCO3, Mg(OH)2) and sulfate (CaSO4) scales are thus prevented from occurring. The two plants have been designed on the basis of extensive evaluations on pilot and laboratory-scale plants briefly described hereafter. The research development includes studies on a combination of hydrolysis and direct exchange Cl-/HCO-3, with the final aim of dealkalizing sea water without fresh acid consumption.

Thermoanalytical study of activated carbon regeneration. II. 0-, m-, p-nitrophenol desorption

Abstract Partial adsorbate release (63, 50 and 53% for o-, m- , and p -derivatives, respectively) occurs when a commercial activated carbon loaded with each nitrophenol isomer is heated between 25 and 950°C in a dynamic N 2 atmosphere. After the endothermic process of water removal below 150°C, three definite steps are associated with adsorbate release. Evaluation of the related energies is presented.