Mineral Recycling Research Articles

Magmatic Enclaves and Andesitic Lavas from Mt. Lamington, Papua New Guinea: Implications for Recycling of Earlier-fractionated Minerals through Magma Recharge

Mt. Lamington is a composite, dome-forming volcano in Papua New Guinea, sitting on the Papuan Ultramafic Belt (PUB) ophiolite. The 1951 eruption produced andesitic dome lavas with numerous basaltic–andesitic enclaves and a few PUB ultramafic xenoliths. To understand the nature of the 1951 eruption, and to assess the effect of assimilating ophiolitic crust in modifying the geochemistry of arc magmas, we carried out petrological, mineralogical and geochemical studies on andesitic lavas as well as magmatic enclaves and ultramafic inclusions. The mineralogy of the enclaves is dominated by amphibole and plagioclase, similar to the andesitic lava hosts. The textures of the enclaves vary from fine-grained diktytaxitic to coarser-grained plutonic textured. We interpret this variation to result from variable cooling rates in the enclave-forming magma body when it invades the overlying andesite. The diktytaxitic enclaves contain variable proportions of host-derived amph + plag antecrysts and xenocrysts of ol + sp ± cpx ± amph with disequilibrium textures, indicating interaction with host lava and assimilation of foreign materials, respectively. A previous study argued that the olivine xenocrysts with chromian spinel inclusions are derived from the PUB, and thus that the PUB contaminated the Mt. Lamington magmas. We demonstrate that this is highly unlikely on the basis of morphological and compositional discrepancies between PUB ol + sp, sampled in nodules, and the xenocrysts. Mass balance indicates that the high whole-rock Ni contents of enclaves and andesitic hosts can be explained by olivine incorporation and do not require any PUB involvement. The olivines are considered to represent crystal mush fractionated from precursor(s) of andesitic and/or pre-1951 shoshonitic lavas. Their presence in enclaves represents recycling of earlier-fractionated components through magma recharge. We argue that this recycling is an important and underestimated process in shaping arc magmas.

40Ar/39Ar ages and geochemical characterization of Cretaceous bentonites in the Nanushuk, Seabee, Tuluvak, and Schrader Bluff formations, North Slope, Alaska

Diagenetically altered volcanic ash deposits (bentonites) found in Cretaceous terrestrial and marine foreland basin sediments have the potential to be used for chronostratigraphy and subsurface correlation across Alaska's North Slope. Detailed age and geochemical studies of these volcanogenic deposits may also shed light on the tectonic evolution of the Arctic. Though these bentonites have been previously studied, there are few published results for regional bentonite ages and geochemistry due to challenges of dating weathered volcanic ash. We analyzed mineral separates from cored bentonites recovered from wells in the National Petroleum Reserve Alaska. The analyses confirm that an intense period of volcanic ash deposition on Alaska's North Slope began by the late Albian and persisted throughout the Cenomanian, an interval of rapid progradation and aggradation in the Colville basin. These results also add to a sparse record of radioisotopic ages from the Nanushuk Formation. A bentonite preserved in delta plain sediments in the upper Nanushuk Formation dates to 102.6 ± 1.5 Ma (late Albian), while a bentonite near the base of the overlying Seabee Formation was deposited at 98.2 ± 0.8 Ma, in the early Cenomanian. The two ages bracket a major flooding surface at the base of the Seabee Formation near Umiat, Alaska, placing it near the Albian-Cenomanian boundary (100.5 Ma). Several hundred feet up-section, the non-marine Tuluvak Formation contains bentonites with 40Ar/39Ar ages of 96.7 ± 0.7 to 94.2 ± 0.9 Ma (Cenomanian), several million years older than previously published K–Ar ages and biostratigraphic constraints suggest.Major and trace element geochemistry of a sub-sample of six bentonites from petroleum exploration wells at Umiat show a range in composition from andesite to rhyolite, with a continental arc source. The bentonites become more felsic from the late Albian (∼102 Ma) to late Cenomanian (∼94 Ma). A likely source for the bentonites is the Okhotsk-Chukotka Volcanic Belt (OCVB) of eastern Siberia, a continental arc which became active in the Albian and experienced episodes of effusivity throughout the Late Cretaceous. Chronostratigraphically anomalous 40Ar/39Ar ages coincide with peaks of magmatic activity in the OCVB, suggesting that these anomalously old ages may be due to magmatic contribution of xenocrysts or recycling of detrital minerals from older volcanic events. An alternative explanation for the chronostratigraphically anomalous ages is mixing of bentonites with detrital sediment derived from unroofing and erosion of metamorphic rocks in the Brooks Range, Herald Arch, and Chukotka throughout the mid to Late Cretaceous.

Hydrothermal synthesis of lithium silicate (Li2SiO3) from waste glass: a preliminary study

Current environmental directives to conserve resources and to divert waste streams have generated significant interest in mineral recycling. In this respect, this preliminary study has demonstrated that lithium metasilicate can be prepared by hydrothermal reaction between waste container glass and lithium hydroxide solutions at 100 °C. Minor proportions of calcium hydroxide, calcite, lithium carbonate and tobermorite were also produced during the reaction. Percentage crystallinity and proportion of lithium metasilicate in the reaction product were found to increase as functions of lithium hydroxide concentration (between 1 and 4 M). This research has also shown that the lithium metasilicate phase can take up 6.4 mmol/g of Zn2+ ions after 24 h during batch sorption. Further work to optimise the yield and to appraise the antimicrobial properties of Zn2+-bearing lithium metasilicate is now warranted.

The impact of mining on the environment in Poland – myths and reality

Abstract Mining is always connected with interference in the environment, especially with the landscape, hydrosphere and atmosphere. The increasing requirements of environmental standards in Europe influence actions taken by the mining industry, which leads to minimization of impact during exploration, exploitation, processing and use of raw materials and waste. Moreover, mining companies often compensate the environment transformations via the processes of reclamation and adequately chosen directions of further adaptation. New post-mining areas are characterized, in many cases, by higher values than before the commencement of mining works. The problem is still the depletion of non-renewable raw materials. This can be minimized by rational resource management and also by the effective use, recovery, recycling and substituting of minerals. These actions will have an impact not only on the extension of the operation of existing plants, but will also diminish the areas needed for extraction of new deposits. In the paper, the transformations taking place in the mining industry in Poland, as well as myths and threats connected with its further development were pointed out. The actions by this industrial branch which lead to minimization of the pressure on the environment and the applied reclamation were also shown.

Petrological and Geochemical Constraints On Provenance, Paleoweathering, and Tectonic Setting of the Neoproterozoic Sedimentary Basin In the Eastern Jiangnan Orogen, South China

Abstract The Neoproterozoic (830–815 Ma) Shuangqiaoshan (SQS) and (833–817 Ma) Xikou (XK) groups are two of a series of sedimentary sequences in the Jiangnan Orogen, which are located in the southeastern Yangtze Block, South China and witnessed the assemblage and breakup of the supercontinent Rodinia. Through a multidisciplinary approach, including petrology and geochemistry of the clastic sedimentary rocks, we reconstruct the sedimentary provenance and paleoweathering of the sedimentary basin and characterize the formation and evolution of the Jiangnan Orogen and its role in Rodinia. The SQS Group consists of texturally immature sandstones composed of unsorted and angular to subangular clastic grains dominated by lithic fragments (54–80%) (mostly chert, metasedimentary, and sedimentary grains) accompanied by variable amounts of quartz (14–40%) and feldspar (0–18%). Sandstones from the XK Group are characterized by lower quartz (5–16%) but higher feldspar (16–47%) and lithic fragments (47–78%) (mostly volcanic detritus). All samples lie along a provenance-dependent compositional trend, suggesting that hydraulic sorting and recycling of heavy minerals were insignificant. Moderate Eu/Eu* (0.6–1.0) and (La/Yb)n (4.8–8.4) values and predominant Neoproterozoic euhedral detrital zircons indicate that sedimentary detritus was largely sourced from locally distributed Neoproterozoic intermediate to felsic igneous rocks. Potential sources include the ca. 930–900 Ma Pingshui plagiogranite, the ca. 930–890 Ma Shuangxiwu andesite, and the ca. 850 Ma Zhenzhushan dacite and basalt. The modeled average composition of the SQS detritus consists of 80% dacite, 10% andesite, and 10% basalt, whereas the XK detritus consists of 70% dacite, 20% andesite, and 10% basalt. The SQS and XK rocks record mild to moderate chemical weathering in their source areas. Some samples plot away from the predicated weathering trend in the A-CN-K diagram, reflecting replacement of the detrital calcic plagioclase by authigenic albite during postdepositional metasomatism. Textural and chemical immaturity, non-steady-state weathering, and signatures of immobile elements are indicative of a tectonically active setting, likely a continental arc environment, for deposition of the SQS and XK groups. The Yangtze Block is thus considered to be located in the periphery of Rodinia during ca. 833–815 Ma.

Diamond industry wastes: Mineral composition and recycling

Samples from eighteen kimberlitic bodies of Russia (Archangelsk and Yakutia provinces) and China (Liaonin and Shandong provinces) were investigated. All investigated kimberlites were subdivided into four mineralogical-technological types, according to the data obtained: (1) rocks with dominant saponite (Chidviya and Lomonosov pipes), (2) high-serpentine rocks (Snegopadnaya, Aikhal, Dalnyaya, and Udachnaya pipes), (3) rocks with high levels of carbonate and phlogopite (Chernyshevsk and Botuoba pipes), and (4) rocks with a complex mixed structures (Morkoka, 23 S”ezd KPSS, Nyurba, Mir pipes and pipes of China). A recycling scheme is offered for each type of kimberlitic rocks.

Phytosociological behaviour and mineral allocation in Panicum turgidum Forssk. along the coast of the Arabian Gulf, Kuwait

AbstractThis study aims at analyzing the phytosociological behaviour, nutrient element allocation and soil‐plant relations of the Panicum turgidum, which inhabits the arid region of Failaka Island and Jal Az‐Zor along the coastal plain of Kuwait. The above and underground parts of P. turgidum, at 21 different sites distributed across two different localities, as well as surrounding soil, were analyzed. TWINSPAN, DCA and CCA multivariate techniques were applied to the plant species and soil data set, with all statistical calculations using SAS software. Multivariate analysis led to the identification of 4 vegetation groups associated with the distribution of P. turgidum. These groups were: Stipagrostis ciliata‐Cakile arabica, Plantago boissieri, Cyperus conglomeratus and Alhagi graecorum. The above and underground parts of P. turgidum in Failaka showed the presence of a wider range of mineral nutrients, whereas in Jal Az‐Zor there was a greater concentration of heavy metals in the analysed plant parts. These results suggested that Failaka, as an isolated island, exhibited better environmental conditions for the growth of P. turgidum with a more efficient uptake, use and recycling of minerals compared with the Jal Az‐Zor in which heavy metals tended to accumulate in the plants and soil (Br, Zn, Fe and Cu). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Test of Bone Mobilization Relative to Reproductive Demand: Skeletal Quality Is Improved in Cannibalistic Females with Large Litters

In species with repeated bouts of reproduction, a female's ability to retain sufficient tissue for self-maintenance is essential to her survival and capacity for future reproduction. Loss of bone mineral content results in bone fragility and the possibility of reduced survival, so females should guard against the overuse of their bone mineral during reproduction. Given these constraints, I predicted that bone mobilization would increase with litter size in mice but plateau before maximum litter size was reached. To test this idea, I manipulated the litter sizes of house mice on the day of parturition to 3, 8, 13, and 18 offspring. At weaning, I euthanized the females and calculated whole-body and bone mineral composition. The total mineral content of females' femurs dropped as litter size increased to the average litter size for this strain of mouse (13) but surprisingly, femoral mineral content was higher for females assigned the largest litter sizes (18). Seven of the nine females assigned 18 young cannibalized some of their offspring. For females assigned to these larger litters, femoral ash content was not correlated with number of young consumed, suggesting that mineral recycling had little effect on final bone mineral content. However, nursing effort (accounting for young lost to cannibalism) was correlated with maternal femoral ash at weaning. These finding suggest that the high bone mineral content of females assigned the largest litters was associated with a reduction in endogenous mineral allocated to the litter.

Ordering Renewable Resources: Groundwater, Recycling, and Desalination

Abstract Optimal recycling of minerals can be thought of as an integral part of the theory of the mine. In this paper, we consider the role that wastewater recycling plays in the optimal extraction of groundwater, a renewable resource. We develop a two-sector dynamic optimization model to solve for the optimal trajectories of groundwater extraction and water recycling. For the case of spatially increasing recycling costs, recycled water serves as a supplemental resource in transition to the steady state. For constant unit recycling cost, recycled wastewater is eventually used as a sector-specific backstop for agricultural users, while desalination supplements household groundwater in the steady state. In both cases, recycling water increases welfare by shifting demand away from the aquifer, thus delaying implementation of costly desalination. The model provides guidance on when and how much to develop resource alternatives.

Leaching standards for mineral recycling materials – A harmonized regulatory concept for the upcoming German Recycling Decree

In this contribution we give a first general overview of results of recent studies in Germany which focused on contaminant leaching from various materials and reactive solute transport in the unsaturated soil zone to identify the key factors for groundwater risk assessment. Based on these results we developed new and improved existing methods for groundwater risk assessment which are used to derive a new regulatory concept for the upcoming “Decree for the Requirements of the Use of Alternative Mineral Building Materials in Technical Constructions and for the Amendment of the Federal Soil Protection and Contaminated Sites Ordinance” of the German Federal Ministry of Environment. The new concept aims at a holistic and scientifically sound assessment of the use of mineral recycling materials (e.g., mineral waste, excavated soils, slag and ashes, recycling products, etc.) in technical constructions (e.g., road dams) and permanent applications (e.g., backfilling and landscaping) which is based on a mechanistic understanding of leaching and transport processes. Fundamental for risk assessment are leaching standards for the mineral recycling materials. For each application of mineral recycling materials specific maximum concentrations of a substance in the seepage water at the bottom of an application were calculated. Technical boundary conditions and policy conventions derived from the “German precautionary groundwater and soil protection policy” were accounted to prevent adverse environmental effects on the media soil and groundwater. This includes the concentration decline of highly soluble substances (e.g., chloride and sulphate), retardation or attenuation of solutes, accumulation of contaminants in sub-soils and the hydraulic properties of recycling materials used for specific applications. To decide whether the use of a mineral recycling material is possible in a specific application, the leaching qualities were evaluated based on column percolation tests with various samples and compared with application-specific maximum concentrations. In the upcoming federal decree this simplified concept is realized using detailed tables which classify the leaching quality of mineral recycling materials and demonstrate potential application. A quality assurance system will be mandatory which defines specific testing programs (material properties and limit concentrations to be tested, number and schedule of testing) for the different mineral recycling materials using standardized methods (column percolation test).

Book Reviews

Book Reviews

Similarities and synergies between mineral processing and recycling of Construction and Demolition Waste

Recycled aggregates from Construction and Demolition Waste (C&DW) can replace natural aggregates in applications such as road construction and concrete production, but in the latter instance there are stringent quality requirements. This paper proposes the application of mineral dressing concepts to the characterisation of C&DW. The main strengths and drawbacks of dry and wet separation processes are presented. Jigging is shown to be a promising method for C&DW beneficiation. Indicators such as Los Angeles index, Shape Index and concrete compressive strength are proposed for monitoring recycled aggregate quality. Similarities and synergies between mineral processing and C&DW recycling are finally outlined.

Annual nutrients budget for the grazed and ungrazed sites of an alpine expanse in North-West Himalaya, India

This work was undertaken to analyze nutrient contents of vegetation in an alpine meadow—Tungnath, North-West Himalaya, India. The study pertains to the uptake, transfer and release of four main macronutrients (organic carbon, total nitrogen, total potassium and total phosphorus) in grazed (exposed to extensive grazing by cattles) and ungrazed (grazing completely prohibited) communities. Mineral concentration was recorded higher for the ungrazed sites compared to the grazed sites, and maximum standing state of nutrients was found in roots. Belowground compartment (roots) contributed maximum share of mineral elements to soil. Litter nutrients release was low because of low microbial activity and continuous removal of phytomass. Observations reveal that there was very little amount of nutrient release from phytomass and vegetation in alpine are very poor source of mineral recycling. Low transfer rate of minerals from one compartment to other is adequate for greater amount of these minerals that are translocated back into the storage organs. A small proportion get removed through rain splash or through the removal of hay during grazing as relatively high release rates in ungrazed sites when compared to grazed sites was observed. This translocation can be considered as an important adaptation in alpine plants for survival during adverse environmental conditions, against all types of biotic pressures and also for regeneration in the forthcoming growing season.

What Factors Have Changed Japanese Resource Productivity?

SummaryIn 2003, the Fundamental Plan for Establishing a Sound Material‐Cycle Society was developed; it established indicators and numerical targets for each of three aspects of material flows in Japan. One of the three indicators is resource productivity: Gross domestic product divided by direct material input (GDP/DMI). This article elucidates factors that have changed recent resource‐use intensity (the inverse of resource productivity) in Japan. Specifically, the analysis emphasizes decomposing resource‐use intensity into the factors of recycling, induced material‐use intensity, demand structure, and average propensity to import. Conclusions drawn from analyses of data from the 1995–2002 period are as follows: (1) Changes in the structure of demand (i.e., the magnitude of the demand for a particular set of goods and services relative to total demand) produced the largest contribution to a reduction in resource‐use intensity. In addition, the aggregate of the decline in induced material‐use intensity and the improvement in recycling contributed as much as changes in the demand structure. (2) Final demand for construction declined steadily during the study period, resulting in the largest contribution to the decline in resource‐use intensity. (3) Final demand for machinery and services increased, whereas their induced material‐use intensity declined, contributing to the decline in resource‐use intensity as a whole. (4) Although the effects of recycling are not great, the increased recycling of nonmetallic minerals contributed to the decline in resource‐use intensity.

Isotopic and textural discrimination between hypogene, ancient supergene, and modern sulfates at the Questa mine, New Mexico

Abstract Chemical and mineralogical changes due to pyrite weathering are of interest with respect to understanding long-term physical stability of mine rock piles at the Questa mine, New Mexico. The ability to discriminate between ancient and modern processes is important for establishing the extent of modern weathering within the piles. Initial inventories of sulfur minerals and representative isotope compositions in rocks from orebodies, the hydrothermal alteration zones associated with orebodies, hydrothermal alteration scars, and mine rock piles were determined. Ore body sulfides have δ 34 S CDT of 0 ± 4‰, typical for sulfides formed by magmatic processes in stockwork Mo systems. Pyrite from alteration scars has a wide range of δ 34 S values from 0.0‰ to −13.6‰. Sulfate from the ore body has markedly positive δ 34 S (5–10‰) accompanied by positive δ 18 O SO 4 values (6–15‰) reflecting equilibrium formation from magmatic fluids. Sulfates from alteration scars have δ 34 S values over a broad range, similar to alteration scar pyrites, from −10.6‰ to 0‰ and δ 18 O SO 4 of 0 ± 3‰. Sulfates with fine grained, delicate, and euhedral mineral habits suggesting recent formation within the mine rock piles, have δ 34 S values similar to orebody pyrite and alteration scars but more negative δ 18 O SO 4 values (−3‰ to −10‰). Sulfates from all three sources occur in these piles, and their stable isotope values have proven useful in differentiating them and their environments of formation (i.e., hypogene, ancient supergene, and recent weathering). Correlating the isotopic compositions with textures allows petrographic assessment for the origins of sulfate minerals in the rock piles, but this must be applied with caution because some sulfate mineral recycling has occurred.

Digital visual simulation for design of mineral and metal recycling processes and of secondary products

The paper presents an overview of a digital approach to enable prediction of the behaviour of complex multi-component three-dimensional components in separation or assembly processes. By digitising the form of individual objects, systems properties (flow, packing, separation) can be simulated to enable optimisation of design of the recycling process. Visual libraries of the components can be established either by direct video capture and suitable three-dimensional transcription or through use of computer aided drawings or some other digital media method. Once in a voxelated format, these component objects can be used within a computational environment in which the real space is divided into a dense array of voxels and in which the simulation (referred to as DigiPac) is performed in a wholly digital environment. A virtue of the method is that properties can be assigned explicitly to individual objects or voxels comprising the object. Further the computational time is reduced, since the entire simulation space is in a digital format. Two hypothetical examples are used to illustrate application of the methods for: flow and separation of ore components employing a digital discrete element method; and the assembly of new products from materials pieces and chards to create a new functional entity. Reverse engineering of such approaches to enable more predictive emulation of processing scenarios for a given user-defined objective is considered. Such methods offer a means of performing realistic calculations on objects that have hitherto been considered too complex to represent. It is believed therefore that the method offer significant technical advantages to those working in this field.

Beneficiation of graphite fines from moulding factory wastes

As the costs of waste disposal increase, more attention is being placed upon the re-use and recycling of valuable minerals contained within the waste streams. In this article, the waste streams from a moulding factory were treated by physical methods to obtain a re-usable graphite fraction. Multi-gravity separators (MGS) and shaking tables (ST) are being used in coal processing and heavy minerals beneficiation. In the present study, the possibility of using an MGS and ST to separate graphite from moulding sand was analysed as part of such investigations. The effects of changes in different process variables on the concentrate sand content and graphite recovery values were studied. Several parameters, thought to have an effect on the separation were tested. After the ST experiments, a graphite concentrate was obtained having 4.5% sand content with 60.8% recovery. After the investigations carried out by MGS, a graphite concentrate was obtained having 0.95% sand content with 68.0% recovery. The results demonstrated that recovered graphite fractions can be re-used in the factory, thus reducing the quantity of waste and costs.

Mast fruiting and seedling survival of the ectomycorrhizal, monodominant Dicymbe corymbosa (Caesalpiniaceae) in Guyana

In Guyana, we investigated seed output, and resulting seedling establishment and survival, during a 'mast' year, by the ectomycorrhizal, monodominant rainforest canopy tree Dicymbe corymbosa (Caesalpiniaceae), a species with high, synchronous seed production at intermittent years. By utilizing seed traps, the mast seed output, predation, carbon and mineral investment, and masting synchrony were quantified in 2003 in primary D. corymbosa forests. Establishment of seedling cohorts was monitored, and climatic conditions associated with masting were assessed. During 2003, D. corymbosa in the Pakaraima Mountains exhibited high, synchronous seed production with low dispersal and predation. Investment in reproductive biomass was large relative to that in other tropical forests. Recent D. corymbosa reproductive events followed El Nino-induced droughts, with little intervening seed production. Over 12 months, 40% of the 2003 seedling cohort survived. Our results suggest that D. corymbosa has a strongly bimodal fruiting pattern that allows the establishment of a large seedling bank, facilitating persistent monodominance. Resource investment in large seed crops may depend on mineral recycling via ectomycorrhizas, coupled with the reallocation of carbon from vegetative maintenance.

Bacterial role in the decomposition of marine-derived material (penguin guano) in the terrestrial maritime Antarctic

Bacterial decomposition of Adélie Penguin ( Pygoscelis adeliae) guano was followed during 42 days exposure in a rookery in Admiralty Bay, King George Island, South Shetland Islands, Antarctica. Bacterial abundance, both total counts (TC) determined by epifluorescence microscopy, and colony forming units (CFU) determined on nutrient media, was enhanced by an air temperature of between 7 and 11 °C, while temperatures above and below this negatively affected abundance. Optimal temperatures for guano decomposition ranged from 3 to 11 °C. Increasing wind velocity positively influenced photoautotrophic bacteria (TAC: total autotrophic bacteria count); photoautotrophs were enumerated during epifluorescence microscopy by their autofluorescence. Guano dry weight attained the lowest value of 74% of initial dry weight after 20 days in situ exposure. Changes in guano resulted from decomposition of the component fats, proteins, chitin, nitrogen and carbon, as well as of mineral recycling (Ca, P, Mg, and others). All transformations accompanied bacterial growth, with TC and CFU both attaining 10 11 cells g −1 d wt of guano. Total bacterial biomass (TBB) increased from 594 μg C g −1 dry weight in fresh guano, to 9101 μg C g −1 dry weight after 42 days exposure in situ. Mean cell volume (MCV) also increased from 0.236 to 0.343 μm 3. Photoautotrophic bacteria were numerically the smallest TC fraction throughout the incubation, with TAC to TC ratio ranging from 0.01 to 0.22%. Culturable bacteria abundance in guano increased dramatically from 0.28% of TC (in fresh guano) to 26% (3-h day), and 90% (42nd day) of TC. Within the total CFU population, copiotrophic bacteria were ca. two orders of magnitude more abundant than oligotrophic bacteria. Chitinolytic bacteria in guano were detected only late in the incubation; by 42 days, >40% of the initial chitin content remained. This material may comprise a significant fraction of the soil in the penguin rookery. Bacteria cultivated from the penguin guano displayed high morphophysiological diversity.

Sludge thermal oxidation processes: mineral recycling, energy impact, and greenhouse effect gases release

Different treatment routes have been studied for a mixed sludge: the conventional agricultural use is compared with the thermal oxidation processes, including incineration (in gaseous phase) and wet air oxidation (in liquid phase). The interest of a sludge digestion prior to the final treatment has been also considered according to the two major criteria, which are the fossil energy utilisation and the greenhouse effect gases (CO2, CH4, N2O) release. Thermal energy has to be recovered on thermal processes to make these processes environmentally friendly, otherwise their main interest is to extract or destroy micropollutants and pathogens from the carbon cycle. In case of continuous energy recovery, incineration can produce more energy than it consumes. Digestion is especially interesting for agriculture: according to these two schemes, the energy final balance can also be in excess. As to wet air oxidation, it is probably one of the best ways to minimize greenhouse effect gases emission.