Chemical Precipitation Process Research Articles

Electrochemistry of sulfide flotation: Growth characteristics of surface coatings and their properties, with special reference to chalcopyrite and pyrite

Characteristics of surface coatings which form when sulfide minerals react with aqueous solutions in the absence and presence of flotation reagents are discussed. The coatings form by electrochemical and chemical reactions, and dissolution, adsorption, surface reaction and precipitation processes. Of special interest to flotation is the proposed formation of a metal-deficient layer adjacent to the unreacted sulfide mineral and a precipitated layer of metal-hydroxide, oxide, sulfate, etc., adjacent to the solution phase. If the metal-oxide layer does not adhere to the metal-deficient layer collectorless flotation occurs, otherwise not. The characteristics of gangue minerals play a special role in detachment of the oxide under certain conditions. Since both kinetic and thermodynamic factors are involved, an interaction of hydrodynamic and chemical variables occurs. Selected results are discussed, particularly for the chalcopyrite/solution interface.

Nutrient Removal in a Short Retention Time Sewage Treatment Plant

Chemical treatment of sewage water is today often considered as a method for phosphorus reduction and used in combination with biological treatment. The experience in Scandinavia, however, shows that chemical treatment alone gives beside a good phosphorus removal also a high BOD reduction. Due to the very low investment cost for such a process it has been adapted in Scandinavia as an alternative to biological treatment. Where the demand is for greater sewage treatment the most feasible method is to complement the chemical precipitation process with a compact biological treatment. In Sweden the dominating post (and also the simultaneous) precipitation process has in many plants been replaced by a chemical pre-treatment process, because with pre-precipitation most of the organic matter is coagulated and extracted already in the primary clarifier. The energy demand in the biological process will decrease. The organic matter in the sludge will increase, which in an anaerobic digester means more digester gas. The unloading pre-precipitation effect can also give advantages for nitrification. The important BOD/TKN ratio is decreased. It is possible to build up a high sludge age and to upgrade a plant without tank expansion to a nitrifying plant. Pre-precipitation is normally not influencing the readily degradable BOD, which is about 25% of the total BOD and therefore a perfect electron donor for pre-denitri-fication is still available. The pre-precipitated sludge contains 75% of the organic matter in the sewage and can by hydrolysis be converted to readily degradable organic matter, which presents a valuable carbon source for the denitrification process. The hydrolysation process can be performed by, for instance, anaerobic treatment or heat treatment. This paper will review experiences from full-scale applications as well as pilot plant and laboratory studies.

Development of Design Criteria for the Chemical Precipitation Process Applied in Cracow Wastewater Reclamation System

The results of investigation on coagulation as tertiary treatment of secondary effluent in the water reuse process for industrial application are presented. The investigations were carried out at the municipal wastewater plant in the city of Cracow. The experimental model has been operated continuously under dynamic flow conditions; the paper describes the construction of the model as well as the experiences gained during its operation. The investigations which were carried out in the laboratory batch tests are also described. The studies were conducted using alum, ferrous sulphate, lime, an alum combined with lime and ferrous sulphate combined with lime doses. The best effectiveness of orthophosphorous removal was found for alum /96.2 %/ and ferrous sulphate combined with lime /84.2 %/. The best results of permangante COD removal were reached for ferrous sulphate /52 %/ and ferrous sulphate combined with lime /51.3 %/. In the paper the suitability of experimental models and procedure for experimental data evaluation in development of design criteria are presented.

Performance Stability of Small Biological Chemical Treatment Plants

Biological and chemical treatment plants constitute a main portion of the overall number of treatment plants in Norway. The biological and chemical plants are divided into three process groups, simultaneous precipitation and activated sludge, combined precipitation and rotating biological contactors (RBC) and post precipitation and activated sludge. Aluminium sulphate or ferric chloride are the commonly used flocculants in the chemical precipitation process. Effluent data from 174 Norwegian biological chemical treatment plants are evaluated. Compared to the effluent standards for each process group, post precipitation shows the best performance. On an average these plants have the lowest actual utilization of the design capacity. The most important factors that cause the treatment plants not to meet the effluent standards are, poor quality of the sewer system, improper design of the plant and organizational problems. Satisfactory separation of particles, flow equalization and proper operational management, are the basic demands to achieve low effluent concentrations for tot-P and BOD7.

Water quality management in the Ruhr area

AbstractThe Ruhr River is the major source of water supply for the North Rhine‐Westphalian industrial district. To ensure drinking water supply from the river a system of reservoirs has been constructed for low flow augmentation. Five additional river impoundments have been built for the abatement of nonpoint pollution.The Ruhr River Association was established in 1913. Its first task was the reduction of coarse pollution by mechanical treatment plants. Activated sludge plants were introduced as early as 1926. Developments continued and presently tertiary treatment is performed by polishing lagoons on one‐third of the Ruhrverband plants and a programme of storage and subsequent biological treatment of stormwater is underway. One important future task is nutrient removal from municipal wastewater by chemical precipitation and biological processes. Phosphorous concentrations in river water have to be diminished to fight eutrophication while nitrogen must be reduced because of drinking water considerations. Heavy metals have to be further controlled and organically attached halogens have to be diminished.

Chemical Evolution of Water and Brines in Contact with Different Zechstein Salt Formations

ABSTRACTThe paper gives a quantitative description of the chemical reactions, the dissolution and precipitation processes which take place when water or brines come into contact with the main mineral assemblages of the German Zechstein salt formation, rock salt with Ca-sulfates, and the potash beds hartsalz and carnallitite. The results of two large scale in situ dissolution tests are presented. These results have been successfully reproduced by computer modelling using the geochemical code EQ3/6.

Size distribution of iron and manganese species in freshwaters

A recently established technique for size fractionation of particulate matter in freshwaters, based on low volume filtration through Nuclepore filters in the field, has been applied to the study of Fe and Mn species in 3 freshwater lakes and a stream feeding one of the lakes. The technique has also been used in a series of laboratory experiments to provide further insight into the process of particle formation. The results are complemented with scanning electron microscope examination of the particles. The raw data are transformed into mass size distributions, which are generally unimodal, with the major part of the mass confined to a single log unit size range. These size distributions are compared and contrasted with a theoretical model of particle behaviour in a lake. The results suggest that particulate Fe and Mn behave according to particle theory. The observed size distributions represent a balance between hydraulic input/output, aggregation, and gravitational settling, as well as chemical precipitation and dissolution processes. Overall particle aggregation is shown to be a slow process in the waters examined, with a time constant of the order of days. There is evidence for a fairly stable particle regime in the 0.05–0.4 μm size range. Deviations from the unimodal distribution in the epilimnion of the lakes indicate the association of Fe, but not Mn, with phytoplankton. In the waters examined Mn was most frequently found in solution, while Fe was predominantly particulate. These findings are interpreted in terms of the differing redox behaviour of the metals.

Continuous Removal of Heavy Metals by the Lime Sulfurated Solution (Calcium Polysulfide) Process

Abstract A continuous wastewater treatment system was developed for the Lime Sulfurated Solution Process which had already been tested in a batch, stirred tank and ascertained to be an effective chemical precipitation process. The removability of heavy metals was investigated with the continuous treatment system, consisting of a plant composed of H2S desorber, reactor, thickener, sand filter, and H2S desorber. The sulfide ion dissolved in treated water was desorbed as H2S by a mixed gas of air and CO2 and recycled in the reactor to precipitate heavy metals. It has been found that: (1) by the recycling use of H2S, the continuous treatment system can remove heavy metals with less coagulant than in the batch, stirred vessel, (2) desorption of the dissolved sulfide ion by the mixed gas decreases the sulfide ion concentration in the treated water below 0.2 ppb, and (3) the conditions for the removal of heavy metals can be detected immediately by a sulfide ion electrode meter.

The Removal of Heavy Metal, Phosphate, and COD Substances from Wastewater by the Lime Sulfurated Solution (Calcium Polysulfide) Process

Abstract A new chemical precipitation process that had been developed for the removal of heavy metals was extended to the removal of phosphate and COD substances. For simulated wastewater contaminated with heavy metal, phosphate, and COD substances, removal experiments were undertaken in a batch, stirred vessel by using the lime sulfurated solution as a single coagulant. The coagulant, the main component of which is CaSx, decomposes in water on contact with air or CO2 gas, and liberates H2S, CaS2O3, CaCO3, CaSO4, and solid sulfur particles. While heavy metals are precipitated as metal sulfides or hydroxides, phosphate is precipitated as calcium phosphate and COD substances are sorbed on the surfaces of the precipitates and they removed. The experimental findings are as follows: (1) The simulated wastewater contaminated simultaneously with phosphate and cadmium ions can be treated better than that contaminated only with the phosphate ion. Also, the CaSx process is found to be more effective than the Ca(OH)2 process for the removal of phosphate. (2) The removal percentages of COD substances ranged from 40% to 90% according to the sort of substance. The COD removal can be attained by the sorption of the substances mainly on the liberated solid sulfur particles, and partly on the calcium salts.

Conditions for the Precipitation of Heavy Metals from Wastewater by the Lime Sulfurated Solution (Calcium Polysulfide) Process

Abstract A new chemical precipitation process utilizing CaSx solution as a single coagulant was tested for the removal of heavy metals from a batch stirred vessel. The precipitation of heavy metals from the simulated wastewater was investigated under varing conditions of pH, temperature, and heavy metal concentrations. Several agitating speeds were studied for the gases (atmospheric air and CO2 gas) blown into the water to decompose the coagulant (CaSx). The findings are as follows: Heavy metal removal in keeping with the water quality standards in Japan was achieved for the simulated wastewater having pH’s between 3 and 11, and the temperatures from 10 to 85 °C. The agitating speed for optimum removal was found to be 10 Hz. More than 250 ppm of the initial heavy metal concentration gives sufficient removal at stoichiometric quantities of coagulant, while less than 50 ppm of the initial concentration results in rather poor removal owing to the colloidal properties of the metal sulfide or hydroxide. For low concentrations of heavy metals, several units of the coagulant over stoichiometric amount are necessary for sufficient precipitation to achieve the water quality standards.

A Process System for Recycling of Wastewater in University

A new process system is proposed for reuse of the wastewater in a university campus. The process system consists of : a classified intercepting sewers system, a chemical precipitation process for the removal of heavy metals and COD substances by sodium hypochloriteferrous sulfate-sodium hydroxide or calcium polysulfide, an activated sludge process for BOD substances reduction, a large reservoir, precoat filtration of suspended particles removal by diatom and zeolite and an ozonization process for decolorization and deodorization. Economical feasibilities of the proposed process system are briefly assessed.

GOALS IN WASTEWATER TREATMENT1

ABSTRACTWithin a few years all domestic wastewater effluents in the United States will be subjected to a minimum of a properly operated primary and secondary treatment process. This implies a very high degree of removal of the more readily biologically degradable material as measured by the BOD test. This practice will to a large degree negate the value of the BOD test as a pollution parameter. Organic carbon appears to be a more suitable means for determining the strength of a wastewater or for controlling the operation of physical and chemical treatment processes. Studies were conducted to determine the effect of time of passage on the ratio of organic carbon to BOD, COD and carbohydrate. The ratio was found to vary with both time and the state of the sample. The carbon content was reduced to a lesser degree than the other parameters. Organic carbon content appears to correlate better with COD than with BOD. The efficiency of a chemical precipitation process can be determined on the basis of organic carbon removal.

Preparation, Growth, and Study of Ultrafine Ferrite Particles

Ultrafine ferrite particles were prepared by a chemical precipitation process below 100°C in an aqueous medium. The resulting materials were grown hydrothermally at moderate temperatures for extended periods of time. Samples were removed at various times during the growing process and their magnetic and physical properties determined. Coercive forces varied from zero to about 800 oe at room temperature for some hydrothermally grown cobalt ferrites. At liquid nitrogen temperature coercive forces to 10 000 oe were measured. Crystallite size measurements were made by x-ray line broadening. An apparatus to measure hysteresis loops in pulsed fields was constructed and used for measuring magnetic properties of samples difficult to saturate, i.e., cobalt ferrite samples at −196°C. Good agreement was obtained between pulsed fields and dc measurements where samples could be measured by both systems.

EFFLUENT DISPOSAL AT LARGE AND SMALL DAIRIES: Based on a paper read to the Western Section on 28th September, 1954

SummaryTo conclude this paper, the most important points may be summarized as follows.Firstly, pollution by dairy effluents will have to be stopped, not only for reasons of good public relations, but also because of impending trouble for future offenders when recent legislation begins to take effect. Secondly, the best and cheapest way of reducing the size of the problem is to reduce losses in the dairy of milk solids of all sorts, especially by‐products of low cash value but high polluting power. Thirdly, direct disposal of the remaining effluent is always best, where possible, but the only method of doing this which can be unreservedly recommended is by a pipe‐line to the sea or to the sewer of a willing Local Authority. Direct disposal on land may be a tempting method financially, but is only satisfactory in exceptional places, and is always a potential source of complaints from neighbours. Fourthly, for most dairies some kind of effluent purification treatment is unavoidable. At small non‐manufacturing dairies, where sludge disposal is not too difficult, the chemical precipitation process followed by irrigation has the advantage of simplicity and low capital cost. If space is limited, single biological filtration can be used for the final stage instead of irrigation. Scarlett's process of aerobic fermentation followed by biological filtration seems more suitable for larger dairies. The activated sludge process is relatively compact and cheap, but is unsuitable for manufacturing dairies with fluctuating load.Of the various biological filtration systems, in our experience the method of choice, when the load is heavy and where a high quality effluent is essential, is undoubtedly the double‐alternating system. It is unfortunately also very expensive. The cost of filter beds, which is the largest item, can be reduced by using one of the high‐rate systems, but these usually involve a bigger sludge disposal problem and an inferior effluent.Finally, I would like to repeat a plea often made before. An effluent plant should be regarded as part of the normal dairy equipment, and should be cared for like the rest of the factory. It should not be thought of as a mere nuisance, or something to be fitted and forgotten. In our experience, the effluent plant that is best looked after gives the least trouble and the best results. This is not achieved by putting it in charge of the most incompetent odd‐job man in the factory, who is thought fit for nothing better than sewage.

A replica technique in the study of chemical precipitation processes

A replica technique in the study of chemical precipitation processes

A Replica Technique in the Study of Chemical Precipitation Processes

A replica technique has been developed for the electron microscope study of particles of precipitates formed by mixing solutions of chemical reagents. The replica is formed thermally in a thin film of parlodion. A one-step, shadowed replica has been found most satisfactory. The technique has been found suitable for studies of the effect of conditions of observation upon the specimen materials, studies of precipitates such as silver chloride which are known to be unstable during direct observation, studies of precipitates as they exist in the mother liquid; and studies which require detailed observation of surfaces.

Sewage Treatment, Purification, and Utilization

THIS is the work of an advocate of chemical precipitation processes for the treatment of sewage. It cannot claim to be an impartial review of the “sewage question,” for the bias of the author is exhibited in nearly every page. The author is evidently of opinion that his case is likely to derive support from what is known as argumentum ad hominem, or abuse of the other side (those who hold different views from his own). The Rivers Pollution Commissioners come in for a considerable share of these attentions, as the following passages will show:—“Such a man was by nature qualified for a Royal Commissioner, who can never admit that either himself or any of his predecessors can have been mistaken” (p. 165). The spoiling of an effluent from a chemical precipitation process by fermentation of the deposited sediment is spoken of as a result “to gladden the heart, and for once justify the representations of ex-Royal Rivers Pollution Commissioners” (p. 172). “Mr. Bailey-Denton—who seems to be to Prof. Frankland what Ali was to Mahomed and Mr. Grant Allen to Charles Darwin” (p. 79). The Royal Commissioners on Metropolitan Sewage Discharge are alluded to in the following terms (p. 86): “That Commission refused or neglected— and in such a case these two terms are nearly equivalent— to examine fully and fairly into the merits of precipitation.... It would not, or at least did not, visit Aylesbury. It was satisfied to condemn precipitation on the faith of the archaic reports of the Royal Rivers Pollution Commissioners, reports which, if true at the date when written—and this is a fairly strong concession—are demonstrably false if applied, e.g., to the process now in operation at Aylesbury.”

III. On the Causes which seem to have Regulated the Relative Distribution of the Calcareous and Sedimentary Strata of Great Britain, with Special Reference to the Carboniferous Formation

It seems to me that the essential distinctions between limestones and all other kinds of stratified rocks (non-volcanic) are not sufficiently recognised by geologists, for while their differences in chemical composition from other strata and their fossiliferous characteristics are admitted, they are usually classed as simple varieties of sedimentary strata, agreeing in all respects as regards their distribution with the shales, sandstone, and conglomerates, etc., with which they are associated. Far different is the view which I take of them, and in this paper I hope to be able to show that, so far from being naturally associated with the other stratified rocks above referred to, they occupy a sphere of their own, with relations naturally antagonistic to all other kinds of sedimentary materials. In the following remarks I shall make use of the term “sedimentary,” as including strata strictly of mechanical origin, such as “conglomerates, breccias, sandstones, shales, and clays, with their varieties,” and of “calcareous” as including varieties of limestone, whether coralline, crinoidal, shelly, or, like the chalk, formed of impalpable molecules; and in order to arrive at a clear understanding of the relationship of these two groups, let us consider the mode of the formation of each. Calcareous Strata .—Without denying that, in exceptional cases, concretionary limestones have been occasionally formed by some process of chemical aggregation or mechanical precipitation, I hold, with several eminent naturalists, that all the great calcareous formations from Palaeozoic down to recent times are due directly or indirectly to vital agencies. If we This 250-word extract was created in the absence of an abstract