ARTICLE 1: Slurry Classification Basics Employed by Hydro-Mining
Some Slurry Classification Basics Used by Hydro-Mining
By Gilbert Hice
Hydro-Mining’s patented ‘eductor couplings’ act as force multipliers within a casing for extracting stratified ‘lighter’ slurry, helping to lift the more easily suspended slurry up through a borehole’s annulus from a hydraulically-jetted deep placer mining deposit. An eductor coupling is part of an advanced patented pumping system that contributes to the function of moving “lighter suspended” slurry material out of the subsurface borehole excavation site through the annular space (between rod and casing) upwards to the surface for dewatering and additional classification, while heavier material is concentrated in a sump to be recovered using a core barrel. As a relatively basic mining process (with a sonic core drill rig as the primary platform), the Hydro-Mining design applies a stratifying bifurcated recovery system, using both the eductor couplings and a sonic core barrel, to effectively recover deep placer deposits where conventional borehole mining methods have failed. This is partly because two interactive but separate recovery methods are used: 1) sonic core barrel extraction of concentrated heavy elements from a sump being one method, where sump recovery of concentrated “heavier” material is a function of Hydro-Mining’s ability to move suspended ‘lighter’ slurry material out of the mining cavity, and 2) surface recovery of suspended “lighter” slurry material from the mining cavity facilitated by eductor couplings and other forces flushing the “lighter” slurry upwards — mining placer in a new, efficient and eco-responsible way.
Hydro-Mining is a key to ‘green’ mining many known but untouched rich placer deposits, and much more. Understanding certain fundamental parts of the sonic mining system helps one to better appreciate its simple but logical effectiveness (especially considering long-established methods and interactive mechanical systems, e.g. pumps, jetting tools, transition rods, eductor couplings, casing, core barrel, etc.).
Hydro-Mining’s process of subsurface deposit mining is designed to continuously form, agitate, clean and desaturate slurry (using jets) while energizing slurry stratification for slurry extraction from the mining cavity. This is analogous to ‘panning gold’ (especially when using the more efficient conical batea design — see discussion about ‘Gold Panning and Hydro-Mining’) where heavies gravitate to the bottom of the pan (mining cavity floor) and the “lighter” material exits over the pan’s lip (up to the processor), but on a commercial scale and with technological enhancements provided by Hydro-Mining’s design. The general physics applied and strategies are basically the same.
Generally speaking, Hydro-Mining simultaneously applies the kinetic energy of a pressurized fluid stream to ‘excavating’ jets, (which is a proven method to disintegrate and disaggregate a subsurface deposit into a slurry-filled cavity), and also to eductor couplings ‘extracting’ jets, (which help flush up ‘lighter’ slurry out of the cavity through the annulus to the surface). The jetted stream effectiveness is primarily a function of nozzle size/shape, pressure, flow rate and power. Other notable features of jetting effectiveness are standoff distance and jetting angle. Different jetting stream objectives at different depths of the Hydro-Mining operation require different applications and designs of nozzles and their facilitating equipment.
The Goulds Model 3393, seven-stage centrifugal pump, should provide Hydro-Mining (as empirically evidenced by Fly’s and other in situ mining processes described within Dr. G. A. Savanick’s ‘Chapter 22.4 Hydraulic Mining: Borehole Slurrying’, SME Mining Engineering Handbook) with the required mining performance metrics for mining 200 feet deep, 20 cubic yards/hour in a boulder field infused with water. The pump should power: 1) two 0.5inch diameter percussive excavating jets nozzles pushing ~200 gallons/min each (~300ft/sec jet streams) using an effective (~1:3 ratio) short jetting nozzle design, as well as 2) a small ~0.1inch nozzle jet stream bottom shoe jet for agitating the sump contents to enhance heavies concentration, and 3) a variable number of multiple small eductor jet nozzles oriented into the annulus using eductor coupling platforms to facilitate “lighter” slurry extraction. As a result 400-500 gallons/minute of water at 1000psi should be jetted, facilitated by a “governor”, which can be the ITT PumpSmart variable speed drive attachment. The pumping system will make instantaneous adjustments to volume/psi as needed to maintain static flow levels of pressurized water correcting for situational variations which includes integrating small patented eductor coupling jets. Such pump performance should prove adequate for a Hydro-Mining prototype’s jet stream ability to disintegrate placer substrate while facilitating eductor coupling (as a multi-level rod array) motive power. Further, Hydro-Mining will be combining acoustic energy to the traditional Goulds’ centrifugal pump baseline pressure, which should produce multiple enhanced mining effects. This includes sonic pulsing, which should generate added mining power based on established research including production of acoustic resonance of water flow with sonic rod activation, further facilitated by a frustum-shaped transition rod. A one-way valve system isolates the pump from the acoustic energy.
The outside diameter of the sonic rod string (from the water spindle downward to the shoe jet) has a consistent ‘prototype’ external diameter of 4.25” — important because otherwise the rod string and attached apparatus, such as the jetting sub-coupling, could easily get stuck upon trying to extract the rod string from a borehole – just like a syringe needle tip needs to have a consistent radial-axial dimension for easier insertion and extraction through the skin. The sonic rod string has the added benefit of sonic oscillation to reduce external drag, which can help it slip through material better than a syringe needle.
The annulus intake space varies from about 2.0” to 4.00”, acting as a ‘screening classifier mechanism’ as well as the ‘intake’ for the annulus that provides a conduit for suspended slurry extraction to the surface processor. Forcing suspended slurry to the surface requires forces that Hydro-Mining can integrate by combining: 1) the pressure gradient effect as defined in part by the hydraulic head and centrifugal pump power, 2) the eductor jetting array (using Bernoulli’s principle) as provided by the eductor couplings, and 3) the sonic ‘billows’ effect as provided by sonic rod wave fluctuation. Theses multiple components act together to force placer slurry (comprised of water and suspended deposit material) upwards through the annulus to the surface processor for more efficient and less problematic placer gold recovery as compared to using a single dedicated eductor pump in the cavity, with Hydro-Mining using less water and energy while producing greater potential for profit, minimizing environmental impact.
Hydro-Mining is designed to create a hydrocyclone-like process in the mining cavity (which can be similar to but more energized than a trommel) that essentially, by fluid dynamics and jetting excavation, stratifies slurry layers within the borehole mining cavity. Slurry stratification is the ‘first classifier’ step in substrate extraction recovery, which occurs in the mining cavity during excavation. Different slurry layers develop, separating naturally by features of movement, shape and density, some flowing faster that move higher and are more inner centralized layers of usually less dense slurry as compared to slower and lower more dense outer layers. Outer layers of moving slurry are acted upon (in part) by resistance of the cavity wall generating torque between layers within the dynamic massive cyclone of self-degrading stratifying fluidic substrate, with its contents subject to all sorts of conditions and forces, e.g. thermal, acoustic, mechanical, hydraulic and cavity shape. The hydrocyclone-like process feeds suspended material into the ‘intake’ annular space in the upper portion of the cavity through a central vortex, which is the second classifier step while the sump gold trap catches ‘heavy’ material below, which is the third classifier step. In Hydro-Mining – at least three classifying steps of slurry occur before the slurry even leaves the mining cavity. Extraction of heavy concentrated components, (e.g. big gold nuggets that have gravitated into the sump gold trap), occurs by means of a sonic core barrel recovery technique, analogous to recovering heavy black sand and gold that has gravitated into the bottom of a gold pan being recovered using an eye dropper. Agitation and swirling of the material in the gold pan helps concentrate the heavy gold and black sand in the bottom of the pan while elevating the lighter and more suspended material for removal over the rim of the pan. In Hydro-Mining the cavity’s cyclonic forces should funnel and help gravitate and concentrate heavy material into a sump gold trap in the floor of the mining cavity that can be removed periodically and easily using a sonic core barrel, while lighter material is vortexed upwards being separated on the surface for additional valuable metals recovery with water being filtered and recycled.
Within the cavity, just as heavy material gravitates downward with a cyclonic effect, the lighter suspended material of all sizes can potentially be vortexed upwards into proximity of the cavity’s ceiling ‘intake annular space’ which presents the ‘second classifier’ step in slurry extraction recovery, which employs the intake‘s dynamic filtering action, occurring by and within the annulus. The annulus intake and its continuous conduit dimension to the surface is constantly changing in its radial dimensionality as the rod rotates, pulses and moves up and down both within the stable casing and below it. The continuous annular space basically doesn’t get smaller than approximately 2 inches (allowing for a pulse fluctuation of about 1/8”). The annular space can completely close at points of contact between the rod string and the casing string, resulting in an opening up of an adjacent radial space to a 4 inch diameter passage. Using the eductor rule-of-thumb ratio of 1:3 for bridging, design preference is for gravel in the slurry to move through an annulus, which is three times larger than the preferred particulate, like through a 2 inch diameter eductor discharge conduit, passing gravel with a 0.5” – 0.75” minus size. Larger gravel will tend to bridge the annulus and be crushed in the process. Generally speaking, anything much larger than the preferred size should either get crushed inside the space to a more preferred size for movement up through the annulus or lose inertia and fall out of the annulus intake back into the cavity for further degradation within the cavity vortex – again, this describes the ‘second classifier’ step. Lighter suspended material is relatively less dense and less wearing on the rod and casing, as compared to heavier gravel remaining in the cavity, as the lighter suspended slurry material is reduced to proper shape and size with extraction to the surface processor.
Slurry that passes through the annulus to the surface is engaged by the surface processor’s grinder providing a ‘fourth classifier’ step, so on and so forth with surface processing machinations being specific to specific mining recovery objectives, including de-watering for filtering and water recycling back to the high-pressure and high-volume centrifugal pump. Based on a documented ‘demonstration of concept’, water flow parameters can be augmented by sonic head acoustic energy as it passes through the sonic rod. It is expected that enhanced flow metrics can be delivered to a prototypes jetting nozzles using acoustic energy. Just as external surface drag to the rod surface is reduced it is plausible that internal rod resistance to flow will also be reduced using acoustic energy, delivering a more efficient flow for nozzle ejection and improved excavation potential as compared to when it is not utilized.
Effective remediation of slime and filtration of the naturally occurring toxic elements, like mercury, is benefitted by the compact and relatively closed hydraulic circuit used by the Hydro-Mining process. This can also be considered as an important classifying step, acting to preserve a site’s natural integrity. Material used to backfill the borehole mining site can be cleaner than when it was removed. Filtered elements and expansion products can be handled economically in compliance to regulations ensuring preservation of mining surface eco-system integrity with utmost responsibility, and planned accordingly prior to mining for proper handling and disposal as needed. Not all subsurface deposit material, including boulders, needs to be removed from a mining cavity in order to achieve production recovery rates that should be higher than 90%. Site recovery effectiveness can initially be estimated through site sampling and appropriately planned, then monitored and adapted with sump recovery concentrates and processor recovered values to optimize recovery effectiveness specific to each site, minimizing surface impact while achieving maximum production benefit.
So, Hydro-Mining’s new concept for achieving profitable borehole placer mining initially stratifies slurry layers into generally heavier and lighter material layers within the mining cavity. As a result two general tiers of recovery are created: 1) core barrel extraction from the sump, and 2) surface processor extraction through the annulus. Unlike a conventional borehole mining cavity’s floor-oriented eductor pump intake/s (with an unreliable backwash function that can’t always manage unpredictable placer-related boulder blockages), Hydro-Mining’s discharge annulus intake doesn’t encounter boulders on the ceiling, and even if it did (e.g. resulting from a cave-in), boulders should only be an issue for a short period as the excavating jets are moved to the immediate proximity or additional casing is used. Boulders and debris piles need to be effectively dealt with when mining deep placer — they are the challenge that stops current traditional in situ borehole methods from extracting placer deposits reliably. Even if the cavity ceiling caves in, which isn’t likely due to stabilizing hydrostatic equilibrium, Hydro-Mining has several options, including multiple system’s apparatus configurations and variable methods, which includes extension of the casing deeper to work from below upwards. Difficult placer situations present untouched opportunities for this modern in situ mining approach — Hydro-Mining.