{"id":7493,"date":"2024-06-05T16:40:04","date_gmt":"2024-06-05T16:40:04","guid":{"rendered":"https:\/\/northamericanmining.com\/?p=7493"},"modified":"2024-06-24T17:25:15","modified_gmt":"2024-06-24T17:25:15","slug":"the-future-of-sag-mills","status":"publish","type":"post","link":"https:\/\/northamericanmining.com\/index.php\/2024\/06\/05\/the-future-of-sag-mills\/","title":{"rendered":"The future of SAG mills"},"content":{"rendered":"\n

SAG mills are well established in the mining industry with several possible flowsheets featuring them. But these circuits consume significant amounts of energy and water. With alternative grinding options providing a means to decrease energy and water use, <\/strong><\/em>North American Mining<\/strong> asked a group of leading experts for their opinion of the future of these workhorses of the mineral processing world.<\/strong><\/em><\/p>\n\n\n\n

By Jonathan Rowland<\/em><\/p>\n\n\n

\"\"
SAG mills consume significant amounts of power, water, and consumables, and thus pose sustainability- and OPEX-related challenges. Image: FLS.<\/em><\/figcaption><\/figure>\n\n\n

Grinding circuits lie at the heart of the minerals processing flowsheet. And at the heart of the grinding circuit is often the SAG mills. These mills have a long history in the mining industry and are thus well understood from both an operational, maintenance, and consumables (grinding media and mill liners) standpoint, with mines able to achieve high equipment availability and productivity.<\/p>\n\n\n\n

\u201cSince their early application in the 1960s, SAG mills have provided the modern mining industry with workhorses used for most high throughput grinding applications,\u201d Bianca Foggiatto, director of Comminution and Processing at Ausenco, told North American Mining<\/em>. \u201cThese mills can functionally replace most of the crushing equipment in a comminution circuit, resulting in a tight footprint and reducing common issues experienced in fine crushing plants.\u201d<\/p>\n\n\n\n

For all their benefits, however, these workhorses present challenges around energy consumption, water usage, and greenhouse gas emissions. As the mining increasingly looks to balance economic goals with lowering its environmental impact, it is worth asking: what is the future for SAG mills?<\/p>\n\n\n\n

The energy challenge<\/strong>
It is widely recognized that \u201cthe grinding circuit requires the highest power demand within a minerals processing flowsheet,\u201d said Garret Barthold, global product line manager for Horizontal Grinding Mills at FLSmidth. \u201cSAG mills are particularly high consumers of energy and, as a result, there has been a push to improve their energy efficiency.\u201d One example of this trend is the use of improved mill drive technologies, e.g., the use of gearless mill drives (for large SAG mills) or of large, geared drives with low synchronous motors and variable frequency drives.<\/p>\n\n\n\n

\u201cChanging the drive train technology on an existing mill may provide mechanical\/electrical efficiency benefits,\u201d explained the FLSmidth expert. \u201cHowever, this type of modification is disruptive, costly, and often impractical in existing operations. Process optimization upgrades thus tend to be the most prominent avenue for sustainability improvements. These solutions include optimization of mill liner design and\/or the implementation of sophisticated online mill load and charge impact monitoring packages, which help ensure the mill is utilizing the energy consumed in the most efficient way.\u201d<\/p>\n\n\n\n

\u201cA subpar control system could lead to an up to 20% efficiency loss by failing to meet throughput or grind targets,\u201d noted Rajiv Chandramohan, global technical director, Process Optimization and Debottlenecking, at Ausenco. \u201cOn the other hand, implementing effective process control solutions, such as advanced process control (APC) and model predictive control (MPC), enhances stability and efficiency in these circuits. Integrating advanced sensors for real-time ore characterization and wear rate monitoring can further boost circuit performance, as can the use of AI systems to dynamically adjust control parameters based on efficiency metrics like cost per ton and greenhouse gas emissions.\u201d<\/p>\n\n\n\n

<\/p>\n\n\n

\"\"
SAG mills provide the modern mining industry with workhorses able to manage most high throughput grinding tasks. Photo: FLSmidth<\/em><\/figcaption><\/figure>\n\n\n

Indirect energy consumption: Grinding media and wear liners<\/strong>
Reducing indirect energy consumption (and costs) associated with grinding media and wear media consumption is an additional driver in comminution circuit flowsheet selection. As Ausenco\u2019s Foggiatto explained, the production of media and wear liners requires mining, smelting, forging, and transport to site, with each stage contributing to GHG emissions. Indeed, in four to seven weeks of operation, a SAG-ball mill circuit can consume the same weight in steel used to construct the entire milling circuit structure.<\/p>\n\n\n\n

Improving the wear life of mill liners is one way to tackle indirect energy consumption; it also improves mill productivity as downtime for liner replacement is reduced. Sam Hearn, global sales director at Multotec, explained how the company\u2019s use of discrete element analysis (DEM) and finite element analysis (FEA) plays a key role when developing improved liner designs and formulations.<\/p>\n\n\n\n

\u201cDEM software enables us to simulate the interaction between the mill charge and the liners, and to evaluate the liner profile over the life of the liner,\u201d Hearn said. \u201cThe analysis considers a range of variables, such as the ore\u2019s bond work index, its specific gravity, the size of the grinding media, the mill speed, and the slurry density, allowing us to accurately model the performance and wear of our mill liners. This includes predicting the liners\u2019 wear life to avoid unscheduled downtime and to extend the time between replacements.\u201d<\/p>\n\n\n\n

Emphasizing that no two mill liner applications are identical, this simulation \u201ccan guide very specific refinements in the liner design for each customer,\u201d added the Multotec expert. \u201cBut a detailed understanding of the operating conditions is vital to ensure that the final solution delivers optimal results.\u201d<\/p>\n\n\n\n

Hearn concluded by saying that \u201cthe traditional use of steel liners in large SAG mills presents challenges. For instance, there may be bending stress inside the steel liner due to inexact fitting on the mill\u2019s curved surface, and the higher rigidity of steel compared to rubber makes it less than optimal for absorbing the energy of material inside the mill. This is where composite liners come into their own, combining the impact resistance of Hardox 500 steel inserts or chrome-molly casting inserts with the absorption capacity of a specially formulated wear-resistant compound.\u201d<\/p>\n\n\n

\"\"
Pilot scale testing is essential for designing AG milling circuits. Photo: Metso.<\/em><\/figcaption><\/figure>\n\n\n

<\/p>\n\n\n\n

Alternatives to SAG mills: Going fully autogenous<\/strong>
SAG mill-based flowsheets typically have high greenhouse emissions (GHG) associated with two stages of grinding. This makes alternative flowsheets that include autogenous mills or single-stage grinding more attractive.<\/p>\n\n\n\n

\u201cFully autogenous milling requires similar energy inputs as traditional SAG-based circuits, but it uses rocks as grinding media, reducing the indirect GHG emissions associated with grinding media usage,\u201d explained Ausenco\u2019s Foggiatto. \u201cThe selection of autogenous comminution technologies can thus improve project economics and, at the same time, reduce GHG emissions.\u201d<\/p>\n\n\n\n

\u201cAG-pebble and AG-ball milling circuits are increasingly favored for reductions in media consumption, facilitating lower OPEX and reduced carbon intensity,\u201d agreed Nick Green, vice president \u2013 Horizontal Mills at Metso. However, fully autogenous grinding is not appropriate for all ores. Ore testing, such as SMC and Allis-Chalmers media competency test \u201ccan provide some insight into whether an ore is amenable but pilot scale testing under the appropriate conditions is still the gold standard for designing AG milling circuits,\u201d added Green\u2019s colleague, Alan Boylston, director of Process Engineering at Metso.<\/p>\n\n\n\n

Examples of AG-based circuits currently operating provided by Foggiatto include:<\/p>\n\n\n\n

    \n
  • Autogenous primary and secondary milling, e.g. Aitik copper-gold-silver mine in Sweden and Forrestania nickel mine in Australia.<\/li>\n\n\n\n
  • Single stage autogenous milling, e.g. Olympic Dam
    polymetallic mine and Kambalda nickel mine, both in Australia.<\/li>\n\n\n\n
  • Autogenous primary mills and secondary ball milling, e.g. Savage River iron ore in Australia and Ridgeway gold mine in Australia.<\/li>\n<\/ul>\n\n\n\n

    Alternatives to SAG mills: Dry comminution<\/strong>
    When it comes to dry grinding flowsheets, all our experts pointed to the use of HPGRs, with Foggiatto describing them as \u201cthe most energy efficient circuit, although energy requirements for air classification can offset this benefit. Additionally, it has the potential to deliver ground products with narrower size distributions, which in turn can result in improved flotation performance and more effective tailings disposal with lower water consumption. It is not appropriate for all ores, but typically most favorable financially when ores are competent and power cost is high.\u201d<\/p>\n\n\n\n

    HPGR circuits can \u201ccertainly operate with significantly lower energy than AG\/SAG mill circuits,\u201d agreed Green, although \u201cHPGR and other dry comminution technologies are not universally applicable and often SAG mill operation is easier as it reduces material handling requirements.\u201d<\/p>\n\n\n

    \"\"
    Table 1 shows a comparison of different grinding circuit flowsheets for a 4-million-tonnes-per-year copper concentrator designed to process moderate competence and hardness ores.<\/em><\/p>\n\n\n

    In addition to reduced energy consumption, dry grinding circuits can deliver a \u201ca direct reduction in water utilization,\u201d added Barthold of FLSmidth. \u201cHowever, implementation of dry grinding is heavily influenced by downstream unit operations. For flowsheets where downstream separation and filtration are a wet process, conversion of the grinding circuit to a dry arrangement provides minimal benefit to overall plant water consumption. Conversely, dry grinding flowsheets provide significant water reduction benefits in applications with dry downstream minerals separation and refinement.\u201d<\/p>\n\n\n\n

    \u201cThere is a perception that dry grinding reduces water consumption; however, where wet beneficiation is required for liberation, the net water addition is essentially the same, as water is just added later in the process,\u201d affirmed Metso\u2019s Boylston.<\/p>\n\n\n\n

    VRMs are another dry grinding technology. But whereas HGPR has already proven itself in mineral process applications, VRMs have yet to gain full acceptance. Yet the technology has a long and proven history in other applications, for example, the grinding of cement or granulated blast furnace slag. VRMs also produce a steeper particle size distribution, producing a feed well suited to flotation, while reducing waste in the form of ultra-fines and oversize and allowing for a good flotation size range.<\/p>\n\n\n\n

    <\/p>\n\n\n

    \"\"
    Table 2 shows a comparison of the different approaches to design sustainable comminution circuits as compared to typical SAG-based flowsheets.<\/em><\/p>\n\n\n

    Innovative technologies: Improving SAG circuits<\/strong>
    In addition to these alternative grinding technologies, there are \u201cother new technologies currently being employed that improve energy efficiency and water consumption of processing plants,\u201d continued Foggiatto. Importantly, these can be used in conjunction with existing SAG mills to improve energy efficiency.<\/p>\n\n\n\n

    \u201cTechnologies capable of ore\/gangue separation at an earlier stage of the process unlock significant savings in energy and water consumption, as well as producing coarser tailings enabling safer disposal methods,\u201d said Metso\u2019s Boylston, picking up the point. \u201cTo examples here are bulk ore sorting and coarse particle flotation technologies.\u201d<\/p>\n\n\n\n

    Bulk ore sorting (BOS): BOS is a low-capital and low-operating-cost preconcentration method that can effectively sort ore at high throughputs and reduce the amount of material that is ground to fine particles. The broad aim is to \u201ctake advantage of the natural spatial heterogeneity of an orebody to reject low grade material in smaller packet sizes and higher accuracy than current grade control strategies,\u201d explained Ausenco Chief Technical Officer Matt Pyle. \u201cThe mineralogy of the deposit drives the sensor to be employed, which in turn determines the sorting technique. Depending on the BOS technology, the sensor is mounted on a conveyor or the mining fleet (such as a shovel.\u201d Examples of BOS technology suppliers include Metso.<\/p>\n\n\n\n

    Coarse particle flotation (CPF): Conventional flotation \u201crecovers a high proportion of the target mineral in a particle size range of 15 to 100 \u00b5m, but at finer (< 15 \u00b5m) and coarser (> 100 \u00b5m) particle sizes, recovery values are significantly lower,\u201d said Pyle. \u201cThere are however technologies now coming to market for efficient coarse particle flotation. These provide the opportunity to coarsen the comminution circuit grind target or increase mill throughput, while producing coarse tailings for more straightforward dewatering and disposal.\u201d<\/p>\n\n\n\n

    Examples of CPF technologies include Eriez\u2019 HydroFloat, Jord International\u2019s NovaCell, and the Reflux Flotation Cell and CoarseAIR, both from FLSmidth. Metso are also developing a novel flotation technology for CPF, which \u201ccan be applied to simple flowsheets, leading to further reduced water consumption and lower capital and operational costs,\u201d added Boylston.<\/p>\n\n\n

    \"\"
    Coarse particle flotation technologies offer the opportunity to coarsen SAG circuit grind target and\/or increase mill throughput. Pictured: FLS REFLUX Flotation Cell<\/em><\/figcaption><\/figure>\n\n\n

    The future of SAG mills<\/strong>
    In the immediate future, \u201cSAG mills will certainly have their place in minerals processing flowsheets,\u201d concluded FLSmidth\u2019s Garret Barthold. \u201cSAG mills are an established technology that allows for high capacity grinding through single machines. However, as we focus on grinding solutions that provide lower energy consumption and lower water utilization, dry processing solutions will gain more prevalence as mining companies implement and prove alternative flowsheets.\u201d<\/p>\n\n\n\n

    \u201cWhile alternative comminution flowsheets can deliver important reductions in energy, water consumption and GHG emissions, there are other novel approaches that deliver similar reductions by avoiding grinding of low-grade materials or targeting coarser grind sizes circuits,\u201d added Ausenco\u2019s Foggiatto. \u201cIt may therefore not be necessary to replace them to deliver a more sustainable project and SAG mill-based circuits may thus continue to be selected for new projects in conjunction with other innovative solutions, such as BOS and CPF.\u201d<\/p>\n\n\n\n

    <\/p>\n","protected":false},"excerpt":{"rendered":"

    SAG mills are well established in the mining industry with several possible flowsheets featuring them. But these circuits consume significant amounts of energy and water. With alternative grinding options providing a means to decrease energy and water use, North American Mining asked a group of leading experts for their opinion of the future of these workhorses of the mineral processing…<\/p>\n","protected":false},"author":8,"featured_media":7498,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_themeisle_gutenberg_block_has_review":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[1773,2942,120,2941,2940],"coauthors":[1635],"class_list":["post-7493","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-features","tag-bulk-ore-sorting","tag-coarse-particle-flotation","tag-energy-consumption","tag-grinding-circuits","tag-sag-mills"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/northamericanmining.com\/wp-content\/uploads\/2024\/06\/2024-05_Future_of_SAG_mills_image_4_pilot_scale_testing_Metso.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/posts\/7493","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/comments?post=7493"}],"version-history":[{"count":5,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/posts\/7493\/revisions"}],"predecessor-version":[{"id":7627,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/posts\/7493\/revisions\/7627"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/media\/7498"}],"wp:attachment":[{"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/media?parent=7493"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/categories?post=7493"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/tags?post=7493"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/northamericanmining.com\/index.php\/wp-json\/wp\/v2\/coauthors?post=7493"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}