Laboratory Leaching Tests Research Articles

Leachate From Land Disposal of Coal Fly Ash

The results of large-scale lysimeter tests in which two pulverized coal fly ashes (PCFA) have been exposed to natural weather conditions for up to seven years are presented and compared with those of laboratory leaching tests. Laboratory column leaching tests on PCFA show good reproducibility, and comparisons between lysimeter and laboratory leaching results are promising for several salt ions and trace elements in the leachate when expressed in terms of the leachate to solids ratio (L/S). A long-term disposal strategy which takes into account the largely insoluble nature of PCFA is suggested.

Chemical characterization, leach and adsorption studies of solidified low-level wastes

Laboratory and field leaching experiments were conducted on solidified low-level waste from a commercial boiling water reactor. Batch leaching, soil column adsorption, and soil/waste form column experiments were conducted in the laboratory, using small scale cement waste forms and Hanford ground water. The purpose of these experiments was to evaluate the ability of laboratory leaching tests to predict leaching under actual field conditions and to determine which mechanisms (i.e., diffusion, solubility, or adsorption) actually control the concentration of radionuclides in the soil surrounding the waste form. Chemical and radionuclide analyses performed on samples collected from the field and laboratory experiments indicate strong adsorption of 134,137 Cs and 85 Sr onto the Hanford soil. Approximately 0.5% of the available 60Co leached from the waste forms and migrated through the soil with a retardation factor of 1. Chemical constituents present in the reactor waste streams and found at elevated levels in the field and laboratory leachates include: sodium (1383 mg/L), sulfate (2230 mg/L), and nitrate (435 mg/L field only). Plausible solid phases that could be controlling the chemical and radionuclide concentrations in the leachate were identified using the MINTEQ geochemical computer code.

Mineralogical Characterization of Uranium Ore To Evaluate In-Situ Leaching Prospects

Abstract Mineralogical studies of ore samples from Mobil uranium properties in Grants mineral belt (NM) revealed a correlation between certain mineralogical characteristics of the ore and its leaching behavior in the laboratory. Mild alkaline carbonate solutions containing dissolved oxygen gas or hydrogen peroxide were used to leach ore samples. Leaching effects of the uranium minerals and reactive gangue material were investigated by comparing the mineralogical characteristics between pre- and postleach samples. Analyses were made by using the X-ray diffraction method, petrographic microscopic, and scanning electron microscopic (SEM) examinations. In one ore trend where uraninite was the principal uranium mineral, studies showed that (1) the majority of uranium minerals was readily accessible to the leachate on a microscopic scale, (2) the predominant, 1-micron [1-µm] size uraninite crystals were dissolved rapidly during leaching, (3) the minor but locally abundant uranium vanadate species was insoluble in mild alkaline carbonate leachate, and (4) pyrite crystals, with dimensions 10 times greater than the uraninite crystallites, showed some surface etchings. These results indicate that the solubility and microscopic occurrence of uraninite are favorable for high and rapid uranium recovery, while the fraction of uranium contained in the insoluble uranium vanadate phase cannot be recovered under mild leaching conditions. The uraninite apparently dissolved at a much faster rate than pyrite, indicating a favorable initial selectivity of leachate for uranium. Mineralogical studies of the pre-and postleach ore samples correlate well with the laboratory leach tests, which showed 80 to 90% uranium recovery as well as low vanadium and sulfate levels in the effluents.

Disposal of Waste Material – Evaluation in the KHM Project of Short and Long-Term Effects

One of the main objectives of the Swedish Coal-Health-Environment Project is to assess the short and long term effects of the disposal of coal wastes on the environment. The situation described below has been the basis for the discussions, laboratory leaching tests and field studies carried out in the KHM Project. The results of the laboratory works are reported to the conference in a paper by Liem et al, while this paper discusses the water balance and construction measures. Certain trace elements in coal wastes are found in greater concentrations than in normal soils and rocks. As a result of the mineral alteration in the combustion process the mobility of some of the constituents may be higher in the waste than in the coal (or in sediments in general). On the other hand the alkaline properties of the waste reduce the mobility of many elements. Due to the continuous leaching out of buffering substances the pH of the leachate water will vary with time. The construction of trace elements in the leachate from a waste dump, exposed to acid rain, is governed by several factors. Beside the trace element composition and the leaching characteristic of the waste, the buffering capacity, the time and the water balance of the dump are judged to be the main controlling factors.

Marine Disposal of Fly Ash from Coal Fired Power Plants

In order to obtain an evaluation of the environmental impact of a proposed artificial marine island of deposited fly ash a comprehensive research project has been carried out by the Water Quality Institute in cooperation with other institutes. The project involved a number of field investigations designed to yield the information required to predict emissions and ensuing ecotoxicological effects of such an island. This paper treats some project activities which were performed in pursuit of data needed for estimating emissions from various stages of a marine ash island: Dry fly ash characterization, monitoring of operating ash ponds, investigations at old ash ponds, and laboratory leaching test. The results may be used to describe and evaluate emissions from various forms of marine fly ash disposal.

Organic Micropollutants in Effluent Recharge to Groundwater

Groundwater pollution by organic material derived from the recharge of raw, untreated sewage effluent has been studied at the sewage treatment works at Whitchurch in Hampshire. This organic investigation consisted of two parts; the validation of the sampling and analytical techniques and the field investigation. Sampling points for the survey included open boreholes lined with uPVC or mild steel as well as specially designed buried in-situ groundwater samplers of uPVC or stainless steel construction. Laboratory leaching tests show significant pollution of sampled water by nylon and uPVC components and indicate that all plastics must be avoided in sample point construction. The in-situ samplers with stainless steel bodies and PTFE sampling tubes proved satisfactory. The organic field survey showed that the organic pollution plume is coincident with the inorganic plume from the effluent recharge site. The total organic content of the effluent is reduced through infiltration; 85 per cent is removed in the unsaturated zone and a further 14 per cent during 300 m of lateral flow. The number of organic compounds at significant concentrations also is greatly reduced through infiltration. The most persistent micropollutant identified as coming solely from the sewage is dichlorobenzene which is present at about 9 µg/l below the recharge lagoons and 1 µg/l in the pollution plume 300 m from the site.

Prediction of long-term leachability of a solidified radioactive waste from a short-term leachability test by a similitude law for leaching systems

A Similitude Law for Leaching Systems has been developed based on a one-dimensional mass transport theory which includes the processes of diffusion, sorption, and radioactive decay. The similitude law can be used to determine the leaching characteristics of a solidified waste from a laboratory leaching test conducted for a similar test piece and to determine the long-term leaching characteristics of a test piece from the results of a short-term test. A leaching number developed from the similitude law was found to be the key parameter in characterizing leach test systems. A mathematical model based on one-dimensional transport theory was also developed to determine the general leaching characteristics of a solidified low-level radioactive waste in a test leachant. The results were normalized, based on the simililtude law, in a leaching graph which uses the leaching number as a system parameter. The leaching number can be obtained through short-term leaching tests. The normalized leaching graph can be used to determine the leaching characteristics of a solidified waste without undergoing computer simulation or tedious numerical summations of infinite series.

Production of acid water in a lead-zinc mine, Coeur d'Alene, Idaho

The Bunker Hill Mine in Idaho's Coeur d'Alene mining district produces approximately 10 m3/minute of acid water containing high concentrations of heavy metals. Field and laboratory studies indicate that much of the acid water is produced in a single ore body in the upper part of the mine. The ore of this body contains mainly sphalerite, galena, and pyrite in a siderite-quartz gangue. Ground water recharges this ore body through a near-vertical zone of high permeability, which is the result of mining by the caving technique. Ore samples from the caving area contained oxidized forms of iron and produced acid in a laboratory leaching test. Leaching experiments with several ore samples from the mine also indicated that the ratio of pyrite to calcite in the samples strongly controlled the resultant pH values. Oxidation of pyrite to sulfuric acid and compounds of iron is apparently responsible for the production of acid water in the mine. In contrast, dissolution of calcite in water results in a basic solution, with pH around 8.3, that can neutralize the acid produced by the oxidation process. Methods for prevention of acid mine drainage in this and other similar mines are noted.

Geochemical Studies on the Radioactive Sediments. II-III. II. The Uranium Contents in the Natural Waters in the Ningyo-Pass Mining Area

ウランを含有する人形峠堆積層において,現在の地下水等によってどの程度のウランが溶出移動しつつあるかを確認する二とは,第1報の結果および考察とも関連して重要なので,その後掘進の行なわれた峠地区等の坑道内で採水される坑内水およびその付近の地表水系におけるウラン含有量を測定した。この結果1l中数百ないし数μ9のウラン含有量の値を得るとともに,非酸化地帯に存在する鉱石からのウランの溶出が,酸化地帯に存する鉱石からのウランの溶出量にくらべ多い傾向を知り,この事実を裏づけるため,実験室内で両地帯からの試料につき,pHをかえた溶出実験を行なったρ なおウランの2次的富化の問題についても考察を加えた。