Calcium-rich Waste Research Articles

Sustainable pink ink synthesis from calcium rich/eggshell waste: Chromium tin pink sphene

The chromium-doped tin sphene or malayaite (Ca(Sn,Cr)SiO5, PR233) was synthesized by solid-state reaction method at temperatures between 1300 and 1500 °C. Two different pigments were obtained according to the chemical formula CaSn(1-x)SiCrxO5±δ (x = 0.01 and 0.03). Eggshell, calcium-rich wastes (CRW), were utilized as raw material. The eggshell was only washed and milled. In the pigment reactant formula, more than 30% by weight of CRW was used. Pigments were milled by a planetary ball mill with zirconium oxide equipment. The pigments obtained were used as glaze colorants and inks by reducing the particles to micro and nano sizes, respectively. The Dv(90) of pigments milled for glaze application is 7.19–7.98 μm, while it is 660–678 nm for ink application. Micron-sized pigments were mixed with transparent glaze and applied to the engobe-coated ceramic tile with a pool-type film applicator. The inks were applied to engobe-coated and transparent glazed ceramics through the screen printing method. After glaze and ink application, ceramic tiles were fired at 1130 °C. When the color values of glaze application are examined, the values for L*, a* and b* are between 48.9 and 63.8, 18.4–23.5, 1.2–4.6, respectively. In the Ink application, L*, a* and b* are 71.0–81.2, 21.8–12.7 and 0.9–2.8, respectively. Characterization was performed using various devices such as X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission-scanning electron microscopy (FE-SEM), and spectrophotometer. The conducted studies revealed that the calcium requirement for Ca(Sn,Cr)SiO5 pigment was entirely met using CRW, and a ceramic ink suitable for inkjet applications was successfully obtained.

Kinetics and thermodynamic parameters of palm empty fruit bunch pyrolysis promoted by calcium-rich wastes from coastal-marine residue

Kinetics and thermodynamics of palm empty fruit bunch (PEFB) pyrolysis have been determined in the presence of catalyst from clam shell (Anadara sp.) (CS) using thermogravimetric analysis. PEFB pyrolysis occurred in three stages (moisture and volatile removal, cellulose and hemicellulose, and lignin decomposition), with maximum degradation occurring at 200–400 °C. Activation energy calculated using the iso-conversional method varied from 89.80 to 169.63 kJ/mol for Friedman, 66.25–119.79 kJ/mol for FWO, 53.33–96.44 kJ/mol for KAS, and 50.90–92.04 kJ/mol for Starink. Pre-exponential factor values ranged from 104–1017 and 104–1014 s−1 for non-catalytic and catalytic pyrolysis. The thermodynamic parameters values varied from 47.28 to 99.44 kJ/mol for enthalpy, from 98.23 to 151.62 kJ/mol for Gibbs free energy, and from −0.0858 to −0.0808 kJ/mol for entropy. The reaction mechanism is dominantly second-order and complex. The analysis revealed that PEFB and CaO catalyst from CS are efficient biomass and effective catalyst for bioenergy production.

Unlocking the mysteries: Investigating the kinetic mechanism of calcium carbonate formation from phosphogypsum

Apparent inconsistencies exist in the comprehensive utilization of sulfate, indicating a lack of systematic investigation into the relationships between reacting conditions and the structures of materials. This study quantifies the coprecipitation and transformation process during dissolution-carbonation from phosphogypsum (PG) to polymorphs of calcium carbonates (CaCO3) in the presence of NaOH, NH3, and CO2 through a two-step process. The research establishes a framework for characterizing resulting solutions and achieving products. Additionally, the kinetic mechanism of CaCO3 preparation and PG carbonation was established using a new atomistic KMC model, which reconciles discrepancies and predicts dissolution modes approaching equilibrium. Particularly, it predicts the structures and stability of CaSO4 hydrates by leveraging differential solubilities at a molecular level. Subsequent carbonation with CO2 and the calculation of equilibrium relationships under controlled conditions resulted in the production of CaCO3 from CaSO4·2 H2O. Model simulations and parameter optimization for precursors, intermediates, and generators were monitored and compared over time using RS and powder EPR experiments, yielding optical information for investigating the kinetic mechanism. The findings highlight that PG-involved pathways play a role in purification and mineralization, emphasizing the need to reevaluate traditional concepts of utilizing calcium-rich waste and capturing CO2.

Studies on Taguchi’s optimization for biosorbent developed from waste eggshell material for water defluoridation

Excess fluoride intake from drinking water is a serious concern for human health posing mainly dental/skeletal fluorosis and other multiorgan manifestation. Recent research is being focus on developing a new biosorbent from calcium-rich waste materials with thermal treatment for removal from water since it has high affinity and greater potential for deflouridation. The present research developed a new biosorbent from waste eggshell for deflourdation from water. Taguchi’s orthogonal array was used for process variables optimization to acquire the maximum removal. The fluoride uptake capacity of 10.69 and fluoride removal percentage of 86.67% were acquired for the eggshell sorbent at optimum values of process variables of pH: 7 0.1, adsorbate concentration: 15 agitation time: 60 min, eggshell dose: 14 and temperature: 303 K. ANOVA analysis indicates the contribution of process variables in descending order as adsorbate concentration 39.76% > pH 39.33% > temperature 12.34% > biosorbent dose 6.42% > agitation time 2.14%. Freundlich isotherm and second-order kinetic model were best fitted for the sorption of fluoride. Thermodynamic parameters (ΔH = 42.33 and ΔS = 0.240 ) indicate endothermic and spontaneous fluoride sorption. The sorption elution studies with 0.1 N NaOH suggest the eggshell sorbent could be reused up to three cycles. The influence of co-ions was obtained as < < < The eggshell sorbent was also shown feasibility for defluoridation from real water samples.

The Effect of Iron- and Calcium-Rich Waste Rock’s Acid Baking Conditions on the Rare-Earth Extraction

The work investigates the effect of sulfuric acid baking on rare earth element (REE) extraction from two waste rock samples from a phosphate mine. The role of different mineralogical assemblages and the degree of alteration (i.e., weathering), and the behavior of the main impurities–iron, phosphorus, and calcium–on REE extraction are emphasized. For both samples, the sulfuric acid baking at 25 °C, during 15 min, H2SO4:sample (w/w) mass ratio of 0.45:1 is the best condition for achieving the selective leaching of REE. For the iron rich-sample, the increase in temperature reduces REE extraction and increases iron dissolution. The corresponding sulfuric acid consumed by goethite (α-FeOOH) from 25 °C to 160 °C acid baking is ten times higher than that required for the monazite (REEPO4) reaction. Conversely, higher REE and lower iron extraction are observed by increasing (sulfuric acid/sample) mass ratio (0.95:1). Due to the high sulfuric concentration during dissolution, a local saturation zone close to the dissolution front caused the precipitation of iron oxyhydroxides. The calcium-rich sample shows lower REE extraction by leaching (63% maximum) mainly due to the entrapment of REE-bearing minerals by a gypsum layer, and lanthanide’s uptake by calcium sulfate compounds formed during leaching. The results were discussed with the help of a detailed characterization of the residues.

Thermochemical energy storage performance of papermaking soda residue during CaO-CaCO3 cycles

Papermaking soda residue (PSR) is calcium-rich waste produced by the papermaking industry. In this study, the thermochemical energy storage performances of the original PSR and PSR modified with citric acid were investigated under pressurised carbonation during CaO-CaCO3 cycles in a twin fixed-bed reactor. The effects of carbonation pressure, reaction temperatures, and number of cycles on the energy storage performance were also discussed. The modified PSR exhibits higher energy storage capacity than the original PSR. The energy storage performances of the two PSRs are improved with increasing carbonation pressure from 0.1 to 1.1 MPa. The energy storage density and effective conversion of the modified PSR at 1.1 MPa are approximately 2210 kJ·kg-1 and 0.7 after 30 cycles, respectively. The energy storage density of the modified PSR at 1.1 MPa is approximately 156% greater than that of the original PSR at 0.1 MPa. Carbonation and calcination temperatures of 850 °C are suitable for the energy storage of both PSRs. The surface area and pore volume of the modified PSR are 1.84 and 1.75 times those of the original PSR, respectively. The modified PSR is a suitable energy storage material.

Nucleation and growth kinetics of CaCO3 crystals in the presence of foreign monovalent ions

The aim of this work is to study the effect of the presence of different monovalent ions (Na+, NH4+ and K+) on the nucleation and growth rates of CaCO3 precipitation. There is currently great interest in the precipitation of CaCO3 particles reusing CO2 rich flue gases and calcium-rich wastes, which implies the presence of foreign ions that can affect the crystallization process. Unseeded and seeded tests were carried out in a batch system to estimate the nucleation and growth kinetics, respectively. Tests with Na2CO3 and CaCl2 as precursors led to the classical calcite crystallization mechanism via vaterite formation at high supersaturations. On the other hand, the use of (NH4)2CO3 entailed lower pH and the presence of NH4+, which stabilized the vaterite and avoided its transformation into stable calcite crystals. Thus, faster nucleation kinetics by using Na2CO3 were obtained. To estimate the growth rate, tests with two initial seed loadings and types (micro and nano seed) were performed. The growth rate increased with the crystal size and decreased with the magma density. The results indicate that the ion effect on the growth rate seems to be related to the ionic radius of the foreign ion.

Developing carbon-neutral construction materials using wastes as carbon sink

Developing ecofriendly and low-carbon construction materials is essential to meet the ambitious target of global net zero emission by 2050. The concept of using wastes as carbon sink is taking advantage of alkaline solid wastes, which are rich in calcium or magnesium as a medium for absorbing carbon dioxide (CO2), and allowing manufacturing thermodynamically stable carbonate minerals for construction applications. Today, the major practical and successful applications of CO2 in the construction industry are through accelerated carbonation of granulated aggregates and precast concrete blocks manufactured with different proportions of calcium-rich waste materials. CO2 is also used as an activator in speciality nonhydraulic carbonate-binders or directly injected (in a liquid form) into fresh ready-mix concrete to produce a construction material with higher strength and lower carbon footprint. In addition, accelerated carbonation has become a promising approach to improve the quality of crushed concrete waste, and can be reused in new concrete to attain a sustainable concrete life cycle. In this paper, the progress in academic research of using CO2 in wastes and cement-based products as well as the key advantages and limitations related to the large scale application in the construction industry have been discussed in detail.

Accelerated weathering performance of injection moulded PP and LDPE composites reinforced with calcium rich waste resources

This study aims to assess and understand the accelerated weathering performance of injection moulded PP and LDPE composites reinforced with calcium rich waste resources for the first time. Two different calcium rich wastes: FGD gypsum and marble waste are incorporated without any chemical treatment in the polymer matrices. Visual appearance, chemical changes, flexural properties (strength, modulus and elongation) and surface morphology are analysed. Weathered surfaces are studied to analyse the structural changes with morphology by FTIR and SEM. LDPE showed higher visual stability by weathering with enhanced flexural properties for FGD gypsum composites. FTIR analysis revealed that the composites prepared with LDPE had a stabilizing effect on photo-degradation (minimum carbonyl index=1.09–1.14), which correlates well with the results of mechanical testing, showing these composites retained remarkable mechanical properties (retention rate>85%.) after weathering. Visual appearances, physical and mechanical properties of polymer composites are affected by the accelerated weathering condition. UV radiation in combination with temperature, humidity and water spray leads to polymer crystallinity with degradation resulting in weaker interfacial bonding and detachment of filler from matrix. Results show that the flexural strength of weathered FGD gypsum-PP, marble waste-PP and marble waste-LDPE composites decreased about 7–38%, 50–59% and 5–6%, respectively. Flexural strength of the weathered FGD gypsum-LDPE composites increased about 7–12%. The present study implies that both the reinforcements can enhance the properties of PP and LDPE composites after accelerated UV weathering exposure with potential for civil engineering applications. FGD gypsum is more prominent while structural and durability performances are taken into account.

The Processing of Calcium Rich Agricultural and Industrial Waste for Recovery of Calcium Carbonate and Calcium Oxide and Their Application for Environmental Cleanup: A Review

Every year a million tonnes of calcium rich agro and industrial waste are generated around the whole globe. These calcium rich waste like finger citron, shells of cockle, mussel, oysters etc., and egg shell are biological sources which have various organic compounds. The inorganic calcium rich waste includes gypsum, dolomite, sludge etc., which are produced in surplus amount globally. Most of these by-products are mainly dumped, while few are used for land-filling purposes which leads to the pollution. These agro and industrial by-products could be processed for the recovery of calcium carbonate and calcium oxide particles by physical and chemical method. The recovery of calcium carbonate and calcium oxide particles from such by products make them biocompatible. Moreover, the products are economical due to their synthesis from waste materials. Here, in this current review work we have emphasized on the all the calcium rich agro industries and industrial by products, especially their processing by various approaches. Further, we have also focused on the properties and application of such calcium carbonate and oxide particles for the remediation of organic and inorganic pollutants from the environments. The recovery of such particles from these byproducts is considered not only economical and eco-friendly but it also minimizes the pollution present in the form of solid waste.

Influence of electric arc furnace dust and lime kiln waste in Portland cement hydration

Abstract Studies have indicated that the use of electric arc furnace dust (EAFD) results in a delay in the hydration time of Portland cement. Calcium-rich waste such as lime kiln waste (LKW) is one of the techniques used to offset this delay as it accounts for the lack of this element in calcium silicate hydrate (C-S-H) production in the mixture. The objective of this study was to evaluate the influence of electric arc furnace dust (EAFD) and lime kiln waste (LKW) in the hydration process of Portland cement pastes and their influence in setting time and hydration heat. The methodology used required several steps: physiochemical and micro-structural characterization of waste samples; definition and production cement pastes with different levels of waste substitution and a reference paste and evaluation of the cement pastes with respect to setting time and hydration heat. Results showed that the substitution of 1% EAFD with or without LKW presented similar hydration heats as the reference paste. This indicated that EAFD+LKW substitution would not affect substantially the hydration reactions of cement and could allow waste recycling in construction materials.

Utilization of Gaseous Carbon Dioxide and Industrial Ca-Rich Waste for Calcium Carbonate Precipitation: A Review

Technologies for the management of various types of waste and the production of useful products from them are currently widely studied. Both carbon dioxide and calcium-rich waste from various production processes are problematic wastes that can be used to produce calcium carbonate. Therefore, the purpose of this paper is to provide an overview about the state of the development of processes that use these two wastes to obtain a valuable CaCO3 powder. The paper reviews the current research on the use of post-distillation liquid from the Solvay process, steelmaking slag, concrete, cement, and gypsum waste as well as some others industrial Ca-rich waste streams in the calcium carbonate precipitation process via carbonation route. This work is an attempt to collect the available information on the possibility of influencing the characteristics of the obtained calcium carbonate. It also indicates the possible limitations and implementation problems of the proposed technologies.

A critical review to bridge the gaps between carbon capture, storage and use of CaCO3

• The captured CO 2 can be reacted with calcium-rich wastes and brine to produce useful CaCO 3 . • Dry carbonation involves solid-gas interaction with limited access to inner calcium content. • Wet carbonation allows high purity to be achieved using extracting agent. • The particle size and polymorphs are affected by pressure, pH, time, absorbent, and additives. • Hydrophilic CaCO 3 can be hydrophobically modified to expand its uses. Carbon capture, utilisation, and storage (CCUS) is a new strategy to combat climate change. CO 2 sequestration using calcium-rich wastes has been extensively studied since calcium carbonate (CaCO 3 ) can be produced for various. In this review, the gaps between carbon capture technologies and carbonation are thoroughly discussed. Direct carbonation which involves the carbonation of calcium rich particles using CO 2 should be integrated with adsorption, membrane gas separation and cryogenic separation. Wet carbonation should be integrated with absorption and further adjusted to control the particle size and polymorphs. Among the polymorphs, amorphous CaCO 3 nanoparticles have drawn great attention due to their large surface area. The modification of CaCO 3 was then reviewed for increasing demand of hydrophobic CaCO 3 . There are technical gaps exist in CCUS using CaCO 3 , but the current scientific studies proposed some practical strategies for its implementation at large scale with economic feasibility. Membrane technology and alternative absorbent can enhance gas absorption to meet the requirement of wet carbonation for process integration. The economy potential of CaCO 3 should be elevated through particle size reduction, surface area enlargement and chemical functionalisation.

Production of Porous Poly(phospho-siloxo) Networks for Thermal Insulations Using Low-Value Calcium-Rich Wastes as Pore-Forming Agents

This study focuses on the preparation of porous poly(phospho-siloxo) networks for thermal insulation applications using commercial calcium carbonate and calcium-rich wastes such as oyster shell, snail shell and eggshell powders as pore-forming agents. The control and porous poly(phospho-siloxo) networks were prepared by adding phosphoric acid (4 M) as a chemical ingredient to metakaolin containing 0 and 15 wt% of each foaming agents. The final products were monitored using the X-ray diffractometry, infrared spectroscopy, apparent density, absolute density, thermal conductivity, optical microscopy, scanning electron microscopy and mercury intrusion porosimetry. The results show that the thermal conductivity of the control and porous poly(phospho-siloxo) network from commercial calcium carbonate are 0.35 and 0.20 W/mK, respectively. They were higher compared to those from snail shell (0.17 W/mK), eggshell (0.15 W/mK) and oyster shell (0.14 W/mK). The cumulative pore volumes are 211.4, 365.5, 380.6, 389.7 and 393.3 mm3/g for the control and porous specimens from chicken eggshell, commercial calcium carbonate, snail shell and oyster shell powders, respectively. Their total porosity measured by mercury intrusion porosimeter are 30.9, 45.5, 46.0, 45.9 and 45.4%, respectively, whereas those calculated with apparent and true density measured by pycnometer are 34.48, 45.25, 52.74, 50.84 and 52.60%, respectively. The concentrated pore size diameter of the porous sample from eggshell is highest compared to the others. It can be seen that the total porosities measured by mercury intrusion porosimeter of porous specimens are nearly the same trend as well as the thermal conductivity. It was found that the low-value calcium-rich wastes could be used for producing porous poly(phospho-siloxos) networks which could be utilized for thermal insulation applications.

New route for the synthesis of silica-supported calcium oxide catalyst in biodiesel production

This research aims to investigate the role of silica as a support for CaO catalyst in 4 different aspects: determination of optimum parameters, tolerance of water and FFA content, leaching and kinetics evaluation, and reusability of catalyst. Silica was extracted from rice husk by ion exchange method and subsequently impregnated with CaO. The experimental results showed that the supported catalysts exhibit excellent catalytic activity in transesterification of waste cooking oil with high yield of biodiesel, comparable to that of CaO catalyst. This is due to the fact that catalyst with higher surface area produces higher biodiesel yield. The presence of water did not have significant effect on the performance of supported catalysts, as silica can act as catalyst to esterify the FFA. Furthermore, silica support offered the greatest extent of leaching minimization of CaO and it has been proved that the calcium leached species was insignificant in transesterification reaction. Reusability study suggests that the synthesized catalysts can be recycled up for 8 successive runs. In conclusion, employing calcium rich wastes derived CaO impregnated with silica as catalyst showed good potential in catalytic applications with high economic benefits.

Micro-arc oxidation of bioceramic coatings containing eggshell-derived hydroxyapatite on titanium substrate

In the present study eggshells-derived hydroxyapatite (EHA) coatings were successfully produced on Ti6Al4V substrates using micro-arc oxidation process (MAO) at various concentrations of EHA (i.e. 1, 1.5 and 2 g/L) in an electrolyte consisting of tri-sodium orthophosphate. The attributes of the coatings were determine by X-ray diffraction, attenuated total reflectance-fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The adhesion strength was evaluated using micro scratch tester, while the corrosion behavior of the MAO-coated substrates in phosphate buffer solution was determined by an electrochemical method. The results showed that as the EHA concentration increased, this was accompanied by a reduction in the porosity due to the formation of a dense and thick coating layer. This has also resulted in an increased in the surface roughness and degree of crsytallinity of the HA phase. The MAO-coated substrate prepared with 1.5 g/L EHA concentration exhibited a well-formed coating layer with improved adhesive strength and excellent corrosion resistance. The mechanism of EHA-coating formation as well as the enhanced corrosion resistance of the coated substrates were discussed. This research shows the viability of using calcium-rich waste eggshells to produce phase pure HA suitable for coating on Ti6Al4V substrate using MAO method.

Pyrolysis and combustion kinetics of lignocellulosic biomass pellets with calcium-rich wastes from agro-forestry residues

The pyrolysis and combustion kinetics of biomass pellets (i.e., rice husk, herb residue, and wood residue) with the calcium-rich wastes (i.e., CaO, CaCO3, and eggshell) from agro-forestry residues were comparatively studied. During pyrolysis or combustion of biomass, the Ca-rich wastes could slightly influence the decomposition rate in the stage of devolatilization at relatively lower temperatures (e.g., <400 °C). However, the lignin decomposition and the char combustion were obviously influenced by the calcium-based catalysis at higher temperatures (>700 °C). Particularly, the eggshell had a lowest activation energy in the stage of char combustion. The presence of alkali and alkaline-earth metals (AAEMs) in the eggshells might have positive effects on volatile and char combustion. During the combustion, the decomposition temperatures of CaCO3 and eggshell were decreased, thereby favoring to uptake CO2. Furthermore, by identifying the small molecular products, it was found that both CaCO3 and CaO can improve the pyrolysis of RH, but CaCO3 showed better performances, especially on CO2 capture at lower temperatures and on the enhancement of CO production.

Design of low cost semi-crystalline calcium silicate from biomass for the improvement of the mechanical and microstructural properties of metakaolin-based geopolymer cements

Abstract The main objective of this work is to use low-value SiO2 and CaO-rich wastes like rice husk ash and chicken eggshell powders, respectively for producing semi-crystalline calcium silicate with molar ratio CaO/SiO2 equal to 0.4. The prepared valuable semi-crystalline calcium silicate was used as an additive for a replacement level of metakaolin (0, 1, 3, 5, 7 and 10% by mass). The resulting powders were used to synthesize geopolymer cements using hardener obtained by mixing commercial sodium silicate, sodium hydroxide and distilled water. The final products were characterized by compressive strengths, apparent density, X-ray diffractometry, infrared spectroscopy, scanning electron and optical microscope observations. The results show that the compressive strengths of geopolymer cements were between 33.25 and 51.38 MPa. They increase when metakaolin was replaced by 5, 7 and 10% of semi-crystalline calcium silicate, but no significant change was observed on the strengths of geopolymer cements content 0, 1, 3 and 5% of semi-crystalline calcium silicate. The micrograph images of the selected geopolymer cements were homogeneous and compact and the one from 10% of semi-crystalline calcium silicate shows a coarse microstructure. It was found that the low-value silica and calcium-rich wastes such as rice husk ash and eggshell can be used to prepare semi-crystalline calcium silicate. The obtained product could be used as a low-cost additive to enhance the microstructural and mechanical properties of poly(sialate-siloxo) network.

Artificial weathering pools of calcium-rich industrial waste for CO 2 sequestration

Processes of carbonation of calcium-rich aqueous industrial wastes from acetylene production were performed mimicking rock weathering, using the atmospheric carbon dioxide as reactant. This residue was carbonated exposing it to the air in artificial pools with controlled solid-to-liquid and surface-to-volume ratios, and the efficiency of this simple mineral carbonation process was maximized. Considering realistic values of just one acetylene production plant, the intelligent handling of the calcium-rich waste would make it possible to counteract the emission of around 800 t of carbon dioxide per year, so the CO 2 emissions of the acetylene production could be completely compensated and its carbon footprint significantly reduced. X-ray diffraction patterns and thermogravimetric analyses reported the conversion, up to 88%, of the calcium hydroxide into calcium carbonate under atmospheric conditions. So, considering a realistic industrial scale-up, 476 kg of CO 2 could be captured with 1 t of dry waste. The morphology of the grains is resolved by electron microscopy, and can be described as needles 15 nm wide and 200 nm long arranged in grains smaller than 1 micron. We exploit these nanometric textural parameters (nanometric pores and particles having a specific surface area ∼50 m 2/g) to design an efficient carbon fixation procedure. The aim of this work is to propose this simple carbonation technology, based on aqueous alkaline industrial waste, as a contribution to reducing global CO 2 emissions.

Effect of soluble calcium on the determination of the labile metal content of sediments with ion-exchangers

Equilibration of sediments with cation-exchangers results in a transfer of loosely bound labile metal species to the exchanger phase. Dissolution of the matrix is also promoted and selectivity rules suggest that some of the cations released (particularly Ca) could effectively compete with metal ions for exchange sites. This potential source of error has been evaluated by studying synthetic mixtures of Ca 2+ and other metal ions (Cu 2+, Pb 2+, Cd 2+, Zn 2+) and by analysis of two calcium-rich wastes (a calcine and a jarosite). The ion uptake most influenced by calcium competition was that of zinc; uptake of lead was least affected. For minimum error, i.e., optimum transfer of “available” or “labile” metal ion, the level of free Ca 2+ introduced into the solution should not exceed 300 mg/l., and the amount of exchanger added must provide an excess of exchange sites relative to the amount of cations released from the sample. By use of exchangers of different types it is possible to attempt some classification of the labile metal content, e.g., acid-displaced, exchangeable, salts of weak acids.